Docker - Quick Guide
Docker - Overview
Docker is a container management service. The keywords of Docker are develop, ship and run anywhere. The whole idea of Docker is for developers to easily develop applications, ship them into containers which can then be deployed anywhere.
The initial release of Docker was in March 2013 and since then, it has become the buzzword for modern world development, especially in the face of Agile-based projects.
Features of Docker
Docker has the ability to reduce the size of development by providing a smaller footprint of the operating system via containers.
With containers, it becomes easier for teams across different units, such as development, QA and Operations to work seamlessly across applications.
You can deploy Docker containers anywhere, on any physical and virtual machines and even on the cloud.
Since Docker containers are pretty lightweight, they are very easily scalable.
Components of Docker
Docker has the following components
Docker for Mac − It allows one to run Docker containers on the Mac OS.
Docker for Linux − It allows one to run Docker containers on the Linux OS.
Docker for Windows − It allows one to run Docker containers on the Windows OS.
Docker Engine − It is used for building Docker images and creating Docker containers.
Docker Hub − This is the registry which is used to host various Docker images.
Docker Compose − This is used to define applications using multiple Docker containers.
We will discuss all these components in detail in the subsequent chapters.
The official site for Docker is https://www.docker.com/ The site has all information and documentation about the Docker software. It also has the download links for various operating systems.
Installing Docker on Linux
To start the installation of Docker, we are going to use an Ubuntu instance. You can use Oracle Virtual Box to setup a virtual Linux instance, in case you don’t have it already.
The following screenshot shows a simple Ubuntu server which has been installed on Oracle Virtual Box. There is an OS user named demo which has been defined on the system having entire root access to the sever.
To install Docker, we need to follow the steps given below.
Step 1 − Before installing Docker, you first have to ensure that you have the right Linux kernel version running. Docker is only designed to run on Linux kernel version 3.8 and higher. We can do this by running the following command.
uname
This method returns the system information about the Linux system.
Syntax
uname -a
Options
a − This is used to ensure that the system information is returned.
Return Value
This method returns the following information on the Linux system −
- kernel name
- node name
- kernel release
- kernel version
- machine
- processor
- hardware platform
- operating system
Example
uname –a
Output
When we run above command, we will get the following result −
From the output, we can see that the Linux kernel version is 4.2.0-27 which is higher than version 3.8, so we are good to go.
Step 2 − You need to update the OS with the latest packages, which can be done via the following command −
apt-get
This method installs packages from the Internet on to the Linux system.
Syntax
sudo apt-get update
Options
Return Value
None
Example
sudo apt-get update
Output
When we run the above command, we will get the following result −
This command will connect to the internet and download the latest system packages for Ubuntu.
Step 3 − The next step is to install the necessary certificates that will be required to work with the Docker site later on to download the necessary Docker packages. It can be done with the following command.
sudo apt-get install apt-transport-https ca-certificates
Step 4 − The next step is to add the new GPG key. This key is required to ensure that all data is encrypted when downloading the necessary packages for Docker.
The following command will download the key with the ID 58118E89F3A912897C070ADBF76221572C52609D from the keyserver hkp://ha.pool.sks-keyservers.net:80 and adds it to the adv keychain. Please note that this particular key is required to download the necessary Docker packages.
Step 5 − Next, depending on the version of Ubuntu you have, you will need to add the relevant site to the docker.list for the apt package manager, so that it will be able to detect the Docker packages from the Docker site and download them accordingly.
Since our OS is Ubuntu 14.04, we will use the Repository name as “deb https://apt.dockerproject.org/repoubuntu-trusty main”.
And then, we will need to add this repository to the docker.list as mentioned above.
echo "deb https://apt.dockerproject.org/repo ubuntu-trusty main”
| sudo tee /etc/apt/sources.list.d/docker.list
Step 6 − Next, we issue the apt-get update command to update the packages on the Ubuntu system.
Step 7 − If you want to verify that the package manager is pointing to the right repository, you can do it by issuing the apt-cache command.
apt-cache policy docker-engine
In the output, you will get the link to https://apt.dockerproject.org/repo/
Step 8 − Issue the apt-get update command to ensure all the packages on the local system are up to date.
Step 9 − For Ubuntu Trusty, Wily, and Xenial, we have to install the linux-image-extra-* kernel packages, which allows one to use the aufs storage driver. This driver is used by the newer versions of Docker.
It can be done by using the following command.
sudo apt-get install linux-image-extra-$(uname -r)
linux-image-extra-virtual
Step 10 − The final step is to install Docker and we can do this with the following command −
sudo apt-get install –y docker-engine
Here, apt-get uses the install option to download the Docker-engine image from the Docker website and get Docker installed.
The Docker-engine is the official package from the Docker Corporation for Ubuntu-based systems.
In the next section, we will see how to check for the version of Docker that was installed.
Docker Version
To see the version of Docker running, you can issue the following command −
Syntax
docker version
Options
Return Value
The output will provide the various details of the Docker version installed on the system.
Example
sudo docker version
Output
When we run the above program, we will get the following result −
Docker Info
To see more information on the Docker running on the system, you can issue the following command −
Syntax
docker info
Options
Return Value
The output will provide the various details of the Docker installed on the system such as −
- Number of containers
- Number of images
- The storage driver used by Docker
- The root directory used by Docker
- The execution driver used by Docker
Example
sudo docker info
Output
When we run the above command, we will get the following result −
Docker for Windows
Docker has out-of-the-box support for Windows, but you need to have the following configuration in order to install Docker for Windows.
System Requirements
| Windows OS |
Windows 10 64 bit |
| Memory |
2 GB RAM (recommended) |
You can download Docker for Windows from − https://docs.docker.com/docker-for-windows/
Docker ToolBox
Docker ToolBox has been designed for older versions of Windows, such as Windows 8.1 and Windows 7. You need to have the following configuration in order to install Docker for Windows.
System Requirements
| Windows OS |
Windows 7 , 8, 8.1 |
| Memory |
2 GB RAM (recommended) |
| Virtualization |
This should be enabled. |
You can download Docker ToolBox from − https://www.docker.com/products/docker-toolbox
Docker - Installation
Let’s go through the installation of each product.
Docker for Windows
Once the installer has been downloaded, double-click it to start the installer and then follow the steps given below.
Step 1 − Click on the Agreement terms and then the Install button to proceed ahead with the installation.
Step 2 − Once complete, click the Finish button to complete the installation.
Docker ToolBox
Once the installer has been downloaded, double-click it to start the installer and then follow the steps given below.
Step 1 − Click the Next button on the start screen.
Step 2 − Keep the default location on the next screen and click the Next button.
Step 3 − Keep the default components and click the Next button to proceed.
Step 4 − Keep the Additional Tasks as they are and then click the Next button.
Step 5 − On the final screen, click the Install button.
Working with Docker Toolbox
Let’s now look at how Docker Toolbox can be used to work with Docker containers on Windows. The first step is to launch the Docker Toolbox application for which the shortcut is created on the desktop when the installation of Docker toolbox is carried out.
Next, you will see the configuration being carried out when Docker toolbox is launched.
Once done, you will see Docker configured and launched. You will get an interactive shell for Docker.
To test that Docker runs properly, we can use the Docker run command to download and run a simple HelloWorld Docker container.
The working of the Docker run command is given below −
docker run
This command is used to run a command in a Docker container.
Syntax
docker run image
Options
Return Value
The output will run the command in the desired container.
Example
sudo docker run hello-world
This command will download the hello-world image, if it is not already present, and run the hello-world as a container.
Output
When we run the above command, we will get the following result −
If you want to run the Ubuntu OS on Windows, you can download the Ubuntu Image using the following command −
Docker run –it ubuntu bash
Here you are telling Docker to run the command in the interactive mode via the –it option.
In the output you can see that the Ubuntu image is downloaded and run and then you will be logged in as a root user in the Ubuntu container.
Docker - Hub
Docker Hub is a registry service on the cloud that allows you to download Docker images that are built by other communities. You can also upload your own Docker built images to Docker hub. In this chapter, we will see how to download and the use the Jenkins Docker image from Docker hub.
The official site for Docker hub is − https://www.docker.com/community-edition#/add_ons
Step 1 − First you need to do a simple sign-up on Docker hub.
Step 2 − Once you have signed up, you will be logged into Docker Hub.
Step 3 − Next, let’s browse and find the Jenkins image.
Step 4 − If you scroll down on the same page, you can see the Docker pull command. This will be used to download the Jenkins image onto the local Ubuntu server.
Step 5 − Now, go to the Ubuntu server and run the following command −
sudo docker pull jenkins
To run Jenkins, you need to run the following command −
sudo docker run -p 8080:8080 -p 50000:50000 jenkins
Note the following points about the above sudo command −
We are using the sudo command to ensure it runs with root access.
Here, jenkins is the name of the image we want to download from Docker hub and install on our Ubuntu machine.
-p is used to map the port number of the internal Docker image to our main Ubuntu server so that we can access the container accordingly.
You will then have Jenkins successfully running as a container on the Ubuntu machine.
Docker - Images
In Docker, everything is based on Images. An image is a combination of a file system and parameters. Let’s take an example of the following command in Docker.
docker run hello-world
The Docker command is specific and tells the Docker program on the Operating System that something needs to be done.
The run command is used to mention that we want to create an instance of an image, which is then called a container.
Finally, "hello-world" represents the image from which the container is made.
Now let’s look at how we can use the CentOS image available in Docker Hub to run CentOS on our Ubuntu machine. We can do this by executing the following command on our Ubuntu machine −
sudo docker run centos –it /bin/bash
Note the following points about the above sudo command −
We are using the sudo command to ensure that it runs with root access.
Here, centos is the name of the image we want to download from Docker Hub and install on our Ubuntu machine.
─it is used to mention that we want to run in interactive mode.
/bin/bash is used to run the bash shell once CentOS is up and running.
Displaying Docker Images
To see the list of Docker images on the system, you can issue the following command.
docker images
This command is used to display all the images currently installed on the system.
Syntax
docker images
Options
None
Return Value
The output will provide the list of images on the system.
Example
sudo docker images
Output
When we run the above command, it will produce the following result −
From the above output, you can see that the server has three images: centos, newcentos, and jenkins. Each image has the following attributes −
TAG − This is used to logically tag images.
Image ID − This is used to uniquely identify the image.
Created − The number of days since the image was created.
Virtual Size − The size of the image.
Downloading Docker Images
Images can be downloaded from Docker Hub using the Docker run command. Let’s see in detail how we can do this.
Syntax
The following syntax is used to run a command in a Docker container.
docker run image
Options
Return Value
The output will run the command in the desired container.
Example
sudo docker run centos
This command will download the centos image, if it is not already present, and run the OS as a container.
Output
When we run the above command, we will get the following result −
You will now see the CentOS Docker image downloaded. Now, if we run the Docker images command to see the list of images on the system, we should be able to see the centos image as well.
Removing Docker Images
The Docker images on the system can be removed via the docker rmi command. Let’s look at this command in more detail.
docker rmi
This command is used to remove Docker images.
Syntax
docker rmi ImageID
Options
Return Value
The output will provide the Image ID of the deleted Image.
Example
sudo docker rmi 7a86f8ffcb25
Here, 7a86f8ffcb25 is the Image ID of the newcentos image.
Output
When we run the above command, it will produce the following result −
Let’s see some more Docker commands on images.
docker images -q
This command is used to return only the Image ID’s of the images.
Syntax
docker images
Options
Return Value
The output will show only the Image ID’s of the images on the Docker host.
Example
sudo docker images -q
Output
When we run the above command, it will produce the following result −
docker inspect
This command is used see the details of an image or container.
Syntax
docker inspect Repository
Options
Return Value
The output will show detailed information on the Image.
Example
sudo docker inspect jenkins
Output
When we run the above command, it will produce the following result −
Docker - Containers
Containers are instances of Docker images that can be run using the Docker run command. The basic purpose of Docker is to run containers. Let’s discuss how to work with containers.
Running a Container
Running of containers is managed with the Docker run command. To run a container in an interactive mode, first launch the Docker container.
sudo docker run –it centos /bin/bash
Then hit Crtl+p and you will return to your OS shell.
You will then be running in the instance of the CentOS system on the Ubuntu server.
Listing of Containers
One can list all of the containers on the machine via the docker ps command. This command is used to return the currently running containers.
docker ps
Syntax
docker ps
Options
None
Return Value
The output will show the currently running containers.
Example
sudo docker ps
Output
When we run the above command, it will produce the following result −
Let’s see some more variations of the docker ps command.
docker ps -a
This command is used to list all of the containers on the system
Syntax
docker ps -a
Options
Return Value
The output will show all containers.
Example
sudo docker ps -a
Output
When we run the above command, it will produce the following result −
docker history
With this command, you can see all the commands that were run with an image via a container.
Syntax
docker history ImageID
Options
Return Value
The output will show all the commands run against that image.
Example
sudo docker history centos
The above command will show all the commands that were run against the centos image.
Output
When we run the above command, it will produce the following result −
Docker - Working with Containers
In this chapter, we will explore in detail what we can do with containers.
docker top
With this command, you can see the top processes within a container.
Syntax
docker top ContainerID
Options
Return Value
The output will show the top-level processes within a container.
Example
sudo docker top 9f215ed0b0d3
The above command will show the top-level processes within a container.
Output
When we run the above command, it will produce the following result −
docker stop
This command is used to stop a running container.
Syntax
docker stop ContainerID
Options
Return Value
The output will give the ID of the stopped container.
Example
sudo docker stop 9f215ed0b0d3
The above command will stop the Docker container 9f215ed0b0d3.
Output
When we run the above command, it will produce the following result −
docker rm
This command is used to delete a container.
Syntax
docker rm ContainerID
Options
Return Value
The output will give the ID of the removed container.
Example
sudo docker rm 9f215ed0b0d3
The above command will remove the Docker container 9f215ed0b0d3.
Output
When we run the above command, it will produce the following result −
docker stats
This command is used to provide the statistics of a running container.
Syntax
docker stats ContainerID
Options
Return Value
The output will show the CPU and Memory utilization of the Container.
Example
sudo docker stats 9f215ed0b0d3
The above command will provide CPU and memory utilization of the Container 9f215ed0b0d3.
Output
When we run the above command, it will produce the following result −
docker attach
This command is used to attach to a running container.
Syntax
docker attach ContainerID
Options
Return Value
None
Example
sudo docker attach 07b0b6f434fe
The above command will attach to the Docker container 07b0b6f434fe.
Output
When we run the above command, it will produce the following result −
Once you have attached to the Docker container, you can run the above command to see the process utilization in that Docker container.
docker pause
This command is used to pause the processes in a running container.
Syntax
docker pause ContainerID
Options
Return Value
The ContainerID of the paused container.
Example
sudo docker pause 07b0b6f434fe
The above command will pause the processes in a running container 07b0b6f434fe.
Output
When we run the above command, it will produce the following result −
docker unpause
This command is used to unpause the processes in a running container.
Syntax
docker unpause ContainerID
Options
Return Value
The ContainerID of the running container.
Example
sudo docker unpause 07b0b6f434fe
The above command will unpause the processes in a running container: 07b0b6f434fe
Output
When we run the above command, it will produce the following result −
docker kill
This command is used to kill the processes in a running container.
Syntax
docker kill ContainerID
Options
Return Value
The ContainerID of the running container.
Example
sudo docker kill 07b0b6f434fe
The above command will kill the processes in the running container 07b0b6f434fe.
Output
When we run the above command, it will produce the following result −
Docker – Container Lifecycle
The following illustration explains the entire lifecycle of a Docker container.
Initially, the Docker container will be in the created state.
Then the Docker container goes into the running state when the Docker run command is used.
The Docker kill command is used to kill an existing Docker container.
The Docker pause command is used to pause an existing Docker container.
The Docker stop command is used to pause an existing Docker container.
The Docker run command is used to put a container back from a stopped state to a running state.
Docker - Architecture
The following image shows the standard and traditional architecture of virtualization.
The server is the physical server that is used to host multiple virtual machines.
The Host OS is the base machine such as Linux or Windows.
The Hypervisor is either VMWare or Windows Hyper V that is used to host virtual machines.
You would then install multiple operating systems as virtual machines on top of the existing hypervisor as Guest OS.
You would then host your applications on top of each Guest OS.
The following image shows the new generation of virtualization that is enabled via Dockers. Let’s have a look at the various layers.
The server is the physical server that is used to host multiple virtual machines. So this layer remains the same.
The Host OS is the base machine such as Linux or Windows. So this layer remains the same.
Now comes the new generation which is the Docker engine. This is used to run the operating system which earlier used to be virtual machines as Docker containers.
All of the Apps now run as Docker containers.
The clear advantage in this architecture is that you don’t need to have extra hardware for Guest OS. Everything works as Docker containers.
Docker - Container and Hosts
The good thing about the Docker engine is that it is designed to work on various operating systems. We have already seen the installation on Windows and seen all the Docker commands on Linux systems. Now let’s see the various Docker commands on the Windows OS.
Docker Images
Let’s run the Docker images command on the Windows host.
From here, we can see that we have two images − ubuntu and hello-world.
Running a Container
Now let’s run a container in the Windows Docker host.
We can see that by running the container, we can now run the Ubuntu container on a Windows host.
Listing All Containers
Let’s list all the containers on the Windows host.
Stopping a Container
Let’s now stop a running container on the Windows host.
So you can see that the Docker engine is pretty consistent when it comes to different Docker hosts and it works on Windows in the same way it works on Linux.
Docker - Configuring
In this chapter, we will look at the different options to configure Docker.
service docker stop
This command is used to stop the Docker daemon process.
Syntax
service docker stop
Options
None
Return Value
A message showing that the Docker process has stopped.
Example
sudo service docker stop
Output
When we run the above command, it will produce the following result −
service docker start
This command is used to start the Docker daemon process.
Syntax
service docker start
Options
None
Return Value
A message showing that the Docker process has started.
Example
sudo service docker start
Output
When we run the above command, it will produce the following result −
Docker - Containers and Shells
By default, when you launch a container, you will also use a shell command while launching the container as shown below. This is what we have seen in the earlier chapters when we were working with containers.
In the above screenshot, you can observe that we have issued the following command −
sudo docker run –it centos /bin/bash
We used this command to create a new container and then used the Ctrl+P+Q command to exit out of the container. It ensures that the container still exists even after we exit from the container.
We can verify that the container still exists with the Docker ps command. If we had to exit out of the container directly, then the container itself would be destroyed.
Now there is an easier way to attach to containers and exit them cleanly without the need of destroying them. One way of achieving this is by using the nsenter command.
Before we run the nsenter command, you need to first install the nsenter image. It can be done by using the following command −
docker run --rm -v /usr/local/bin:/target jpetazzo/nsenter
Before we use the nsenter command, we need to get the Process ID of the container, because this is required by the nsenter command. We can get the Process ID via the Docker inspect command and filtering it via the Pid.
As seen in the above screenshot, we have first used the docker ps command to see the running containers. We can see that there is one running container with the ID of ef42a4c5e663.
We then use the Docker inspect command to inspect the configuration of this container and then use the grep command to just filter the Process ID. And from the output, we can see that the Process ID is 2978.
Now that we have the process ID, we can proceed forward and use the nsenter command to attach to the Docker container.
nsenter
This method allows one to attach to a container without exiting the container.
Syntax
nsenter –m –u –n –p –i –t containerID command
Options
-u is used to mention the Uts namespace
-m is used to mention the mount namespace
-n is used to mention the network namespace
-p is used to mention the process namespace
-i s to make the container run in interactive mode.
-t is used to connect the I/O streams of the container to the host OS.
containerID − This is the ID of the container.
Command − This is the command to run within the container.
Return Value
None
Example
sudo nsenter –m –u –n –p –i –t 2978 /bin/bash
Output
From the output, we can observe the following points −
The prompt changes to the bash shell directly when we issue the nsenter command.
We then issue the exit command. Now normally if you did not use the nsenter command, the container would be destroyed. But you would notice that when we run the nsenter command, the container is still up and running.
Docker - File
In the earlier chapters, we have seen the various Image files such as Centos which get downloaded from Docker hub from which you can spin up containers. An example is again shown below.
If we use the Docker images command, we can see the existing images in our system. From the above screenshot, we can see that there are two images: centos and nsenter.
But Docker also gives you the capability to create your own Docker images, and it can be done with the help of Docker Files. A Docker File is a simple text file with instructions on how to build your images.
The following steps explain how you should go about creating a Docker File.
Step 1 − Create a file called Docker File and edit it using vim. Please note that the name of the file has to be "Dockerfile" with "D" as capital.
Step 2 − Build your Docker File using the following instructions.
#This is a sample Image
FROM ubuntu
MAINTAINER demousr@gmail.com
RUN apt-get update
RUN apt-get install –y nginx
CMD [“echo”,”Image created”]
The following points need to be noted about the above file −
The first line "#This is a sample Image" is a comment. You can add comments to the Docker File with the help of the # command
The next line has to start with the FROM keyword. It tells docker, from which base image you want to base your image from. In our example, we are creating an image from the ubuntu image.
The next command is the person who is going to maintain this image. Here you specify the MAINTAINER keyword and just mention the email ID.
The RUN command is used to run instructions against the image. In our case, we first update our Ubuntu system and then install the nginx server on our ubuntu image.
The last command is used to display a message to the user.
Step 3 − Save the file. In the next chapter, we will discuss how to build the image.
Docker - Building Files
We created our Docker File in the last chapter. It’s now time to build the Docker File. The Docker File can be built with the following command −
docker build
Let’s learn more about this command.
docker build
This method allows the users to build their own Docker images.
Syntax
docker build -t ImageName:TagName dir
Options
-t − is to mention a tag to the image
ImageName − This is the name you want to give to your image.
TagName − This is the tag you want to give to your image.
Dir − The directory where the Docker File is present.
Return Value
None
Example
sudo docker build –t myimage:0.1.
Here, myimage is the name we are giving to the Image and 0.1 is the tag number we are giving to our image.
Since the Docker File is in the present working directory, we used "." at the end of the command to signify the present working directory.
Output
From the output, you will first see that the Ubuntu Image will be downloaded from Docker Hub, because there is no image available locally on the machine.
Finally, when the build is complete, all the necessary commands would have run on the image.
You will then see the successfully built message and the ID of the new Image. When you run the Docker images command, you would then be able to see your new image.
You can now build containers from your new Image.
Docker - Public Repositories
Public repositories can be used to host Docker images which can be used by everyone else. An example is the images which are available in Docker Hub. Most of the images such as Centos, Ubuntu, and Jenkins are all publicly available for all. We can also make our images available by publishing it to the public repository on Docker Hub.
For our example, we will use the myimage repository built in the "Building Docker Files" chapter and upload that image to Docker Hub. Let’s first review the images on our Docker host to see what we can push to the Docker registry.
Here, we have our myimage:0.1 image which was created as a part of the “Building Docker Files” chapter. Let’s use this to upload to the Docker public repository.
The following steps explain how you can upload an image to public repository.
Step 1 − Log into Docker Hub and create your repository. This is the repository where your image will be stored. Go to https://hub.docker.com/ and log in with your credentials.
Step 2 − Click the button "Create Repository" on the above screen and create a repository with the name demorep. Make sure that the visibility of the repository is public.
Once the repository is created, make a note of the pull command which is attached to the repository.
The pull command which will be used in our repository is as follows −
docker pull demousr/demorep
Step 3 − Now go back to the Docker Host. Here we need to tag our myimage to the new repository created in Docker Hub. We can do this via the Docker tag command.
We will learn more about this tag command later in this chapter.
Step 4 − Issue the Docker login command to login into the Docker Hub repository from the command prompt. The Docker login command will prompt you for the username and password to the Docker Hub repository.
Step 5 − Once the image has been tagged, it’s now time to push the image to the Docker Hub repository. We can do this via the Docker push command. We will learn more about this command later in this chapter.
docker tag
This method allows one to tag an image to the relevant repository.
Syntax
docker tag imageID Repositoryname
Options
Return Value
None
Example
sudo docker tag ab0c1d3744dd demousr/demorep:1.0
Output
A sample output of the above example is given below.
docker push
This method allows one to push images to the Docker Hub.
Syntax
docker push Repositoryname
Options
Return Value
The long ID of the repository pushed to Docker Hub.
Example
sudo docker push demousr/demorep:1.0
Output
If you go back to the Docker Hub page and go to your repository, you will see the tag name in the repository.
Now let’s try to pull the repository we uploaded onto our Docker host. Let’s first delete the images, myimage:0.1 and demousr/demorep:1.0, from the local Docker host. Let’s use the Docker pull command to pull the repository from the Docker Hub.
From the above screenshot, you can see that the Docker pull command has taken our new repository from the Docker Hub and placed it on our machine.
Docker - Managing Ports
In Docker, the containers themselves can have applications running on ports. When you run a container, if you want to access the application in the container via a port number, you need to map the port number of the container to the port number of the Docker host. Let’s look at an example of how this can be achieved.
In our example, we are going to download the Jenkins container from Docker Hub. We are then going to map the Jenkins port number to the port number on the Docker host.
Step 1 − First, you need to do a simple sign-up on Docker Hub.
Step 2 − Once you have signed up, you will be logged into Docker Hub.
Step 3 − Next, let’s browse and find the Jenkins image.
Step 4 − If you scroll down on the same page, you can see the Docker pull command. This will be used to download the Jenkins Image onto the local Ubuntu server.
Step 5 − Now go to the Ubuntu server and run the command −
sudo docker pull jenkins
Step 6 − To understand what ports are exposed by the container, you should use the Docker inspect command to inspect the image.
Let’s now learn more about this inspect command.
docker inspect
This method allows one to return low-level information on the container or image.
Syntax
docker inspect Container/Image
Options
Return Value
The low-level information of the image or container in JSON format.
Example
sudo docker inspect jenkins
Output
The output of the inspect command gives a JSON output. If we observe the output, we can see that there is a section of "ExposedPorts" and see that there are two ports mentioned. One is the data port of 8080 and the other is the control port of 50000.
To run Jenkins and map the ports, you need to change the Docker run command and add the ‘p’ option which specifies the port mapping. So, you need to run the following command −
sudo docker run -p 8080:8080 -p 50000:50000 jenkins
The left-hand side of the port number mapping is the Docker host port to map to and the right-hand side is the Docker container port number.
When you open the browser and navigate to the Docker host on port 8080, you will see Jenkins up and running.
Docker - Private Registries
You might have the need to have your own private repositories. You may not want to host the repositories on Docker Hub. For this, there is a repository container itself from Docker. Let’s see how we can download and use the container for registry.
Step 1 − Use the Docker run command to download the private registry. This can be done using the following command.
sudo docker run –d –p 5000:5000 –-name registry registry:2
The following points need to be noted about the above command −
Registry is the container managed by Docker which can be used to host private repositories.
The port number exposed by the container is 5000. Hence with the –p command, we are mapping the same port number to the 5000 port number on our localhost.
We are just tagging the registry container as “2”, to differentiate it on the Docker host.
The –d option is used to run the container in detached mode. This is so that the container can run in the background
Step 2 − Let’s do a docker ps to see that the registry container is indeed running.
We have now confirmed that the registry container is indeed running.
Step 3 − Now let’s tag one of our existing images so that we can push it to our local repository. In our example, since we have the centos image available locally, we are going to tag it to our private repository and add a tag name of centos.
sudo docker tag 67591570dd29 localhost:5000/centos
The following points need to be noted about the above command −
67591570dd29 refers to the Image ID for the centos image.
localhost:5000 is the location of our private repository.
We are tagging the repository name as centos in our private repository.
Step 4 − Now let’s use the Docker push command to push the repository to our private repository.
sudo docker push localhost:5000/centos
Here, we are pushing the centos image to the private repository hosted at localhost:5000.
Step 5 − Now let’s delete the local images we have for centos using the docker rmi commands. We can then download the required centos image from our private repository.
sudo docker rmi centos:latest
sudo docker rmi 67591570dd29
Step 6 − Now that we don’t have any centos images on our local machine, we can now use the following Docker pull command to pull the centos image from our private repository.
sudo docker pull localhost:5000/centos
Here, we are pulling the centos image to the private repository hosted at localhost:5000.
If you now see the images on your system, you will see the centos image as well.
Docker - Building a Web Server Docker File
We have already learnt how to use Docker File to build our own custom images. Now let’s see how we can build a web server image which can be used to build containers.
In our example, we are going to use the Apache Web Server on Ubuntu to build our image. Let’s follow the steps given below, to build our web server Docker file.
Step 1 − The first step is to build our Docker File. Let’s use vim and create a Docker File with the following information.
FROM ubuntu
RUN apt-get update
RUN apt-get install –y apache2
RUN apt-get install –y apache2-utils
RUN apt-get clean
EXPOSE 80 CMD [“apache2ctl”, “-D”, “FOREGROUND”]
The following points need to be noted about the above statements −
We are first creating our image to be from the Ubuntu base image.
Next, we are going to use the RUN command to update all the packages on the Ubuntu system.
Next, we use the RUN command to install apache2 on our image.
Next, we use the RUN command to install the necessary utility apache2 packages on our image.
Next, we use the RUN command to clean any unnecessary files from the system.
The EXPOSE command is used to expose port 80 of Apache in the container to the Docker host.
Finally, the CMD command is used to run apache2 in the background.
Now that the file details have been entered, just save the file.
Step 2 − Run the Docker build command to build the Docker file. It can be done using the following command −
sudo docker build –t=”mywebserver” .
We are tagging our image as mywebserver. Once the image is built, you will get a successful message that the file has been built.
Step 3 − Now that the web server file has been built, it’s now time to create a container from the image. We can do this with the Docker run command.
sudo docker run –d –p 80:80 mywebserver
The following points need to be noted about the above command −
The port number exposed by the container is 80. Hence with the –p command, we are mapping the same port number to the 80 port number on our localhost.
The –d option is used to run the container in detached mode. This is so that the container can run in the background.
If you go to port 80 of the Docker host in your web browser, you will now see that Apache is up and running.
Docker - Instruction Commands
Docker has a host of instruction commands. These are commands that are put in the Docker File. Let’s look at the ones which are available.
CMD Instruction
This command is used to execute a command at runtime when the container is executed.
Syntax
CMD command param1
Options
Return Value
The command will execute accordingly.
Example
In our example, we will enter a simple
Hello World echo in our Docker File and create an image and launch a container from it.
Step 1 − Build the Docker File with the following commands −
FROM ubuntu
MAINTAINER demousr@gmail.com
CMD [“echo” , “hello world”]
Here, the CMD is just used to print hello world.
Step 2 − Build the image using the Docker build command.
Step 3 − Run a container from the image.
ENTRYPOINT
This command can also be used to execute commands at runtime for the container. But we can be more flexible with the ENTRYPOINT command.
Syntax
ENTRYPOINT command param1
Options
Return Value
The command will execute accordingly.
Example
Let’s take a look at an example to understand more about ENTRYPOINT. In our example, we will enter a simple echo command in our Docker File and create an image and launch a container from it.
Step 1 − Build the Docker File with the following commands −
FROM ubuntu
MAINTAINER demousr@gmail.com
ENTRYPOINT [“echo”]
Step 2 − Build the image using the Docker build command.
Step 3 − Run a container from the image.
ENV
This command is used to set environment variables in the container.
Syntax
ENV key value
Options
Return Value
The command will execute accordingly.
Example
In our example, we will enter a simple echo command in our Docker File and create an image and launch a container from it.
Step 1 − Build the Docker File with the following commands −
FROM ubuntu
MAINTAINER demousr@gmail.com
ENV var1=Tutorial var2=point
Step 2 − Build the image using the Docker build command.
Step 3 − Run a container from the image.
Step 4 − Finally, execute the env command to see the environment variables.
WORKDIR
This command is used to set the working directory of the container.
Syntax
WORKDIR dirname
Options
Return Value
The command will execute accordingly.
Example
In our example, we will enter a simple echo command in our Docker File and create an image and launch a container from it.
Step 1 − Build the Docker File with the following commands −
FROM ubuntu
MAINTAINER demousr@gmail.com
WORKDIR /newtemp
CMD pwd
Step 2 − Build the image using the Docker build command.
Step 3 − Run a container from the image.
Docker - Container Linking
Container Linking allows multiple containers to link with each other. It is a better option than exposing ports. Let’s go step by step and learn how it works.
Step 1 − Download the Jenkins image, if it is not already present, using the Jenkins pull command.
Step 2 − Once the image is available, run the container, but this time, you can specify a name to the container by using the –-name option. This will be our source container.
Step 3 − Next, it is time to launch the destination container, but this time, we will link it with our source container. For our destination container, we will use the standard Ubuntu image.
When you do a docker ps, you will see both the containers running.
Step 4 − Now, attach to the receiving container.
Then run the env command. You will notice new variables for linking with the source container.
Docker - Storage
Storage Drivers
Docker has multiple storage drivers that allow one to work with the underlying storage devices. The following table shows the different storage drivers along with the technology used for the storage drivers.
| Technology |
Storage Driver |
| OverlayFS |
overlay or overlay2 |
| AUFS |
aufs |
| Btrfs |
brtfs |
| Device Manager |
devicemanager |
| VFS |
vfs |
| ZFS |
zfs |
Let us now discuss some of the instances in which you would use the various storage drivers −
AUFS
This is a stable driver; can be used for production-ready applications.
It has good memory usage and is good for ensuring a smooth Docker experience for containers.
There is a high-write activity associated with this driver which should be considered.
It’s good for systems which are of Platform as a service type work.
Devicemapper
This is a stable driver; ensures a smooth Docker experience.
This driver is good for testing applications in the lab.
This driver is in line with the main Linux kernel functionality.
Btrfs
This driver is in line with the main Linux kernel functionality.
There is a high-write activity associated with this driver which should be considered.
This driver is good for instances where you maintain multiple build pools.
Ovelay
This is a stable driver and it is in line with the main Linux kernel functionality.
It has a good memory usage.
This driver is good for testing applications in the lab.
ZFS
To see the storage driver being used, issue the docker info command.
Syntax
docker info
Options
None
Return Value
The command will provide all relative information on the Docker component installed on the Docker Host.
Example
sudo docker info
Output
The following output shows that the main driver used is the aufs driver and that the root directory is stored in /var/lib/docker/aufs.
Data Volumes
In Docker, you have a separate volume that can shared across containers. These are known as data volumes. Some of the features of data volume are −
- They are initialized when the container is created.
- They can be shared and also reused amongst many containers.
- Any changes to the volume itself can be made directly.
- They exist even after the container is deleted.
Let’s look at our Jenkins container. Let’s do a docker inspect to see the details of this image. We can issue the following command to write the output of the docker inspect command to a text file and then view the file accordingly.
sudo docker inspect Jenkins > tmp.txt
When you view the text file using the more command, you will see an entry as JENKINS_HOME=/var/Jenkins_home.
This is the mapping that is done within the container via the Jenkins image.
Now suppose you wanted to map the volume in the container to a local volume, then you need to specify the –v option when launching the container. An example is shown below −
sudo docker run –d –v /home/demo:/var/jenkins_home –p 8080:8080 –p 50000:50000 jenkins
The –v option is used to map the volume in the container which is /var/jenkins_home to a location on our Docker Host which is /home/demo.
Now if you go to the /home/demo location on your Docker Host after launching your container, you will see all the container files present there.
Changing the Storage Driver for a Container
If you wanted to change to the storage driver used for a container, you can do so when launching the container. This can be done by using the –volume-driver parameter when using the docker run command. An example is given below −
sudo docker run –d --volume-driver=flocker
–v /home/demo:/var/jenkins_home –p 8080:8080 –p 50000:50000 jenkins
The –volume-driver option is used to specify another storage driver for the container.
To confirm that the driver has been changed, first let’s use the docker ps command to see the running containers and get the container ID. So, issue the following command first −
sudo docker ps
Then issue a docker inspect against the container and put the output in a text file using the command.
sudo docker inspect 9bffb1bfebee > temp.txt
If you browse through the text file and go to the line which says VolumeDriver, you will see that the driver name has been changed.
Creating a Volume
A volume can be created beforehand using the docker command. Let’s learn more about this command.
Syntax
docker volume create –-name=volumename –-opt options
Options
Return Value
The command will output the name of the volume created.
Example
sudo docker volume create –-name = demo –opt o = size = 100m
In the above command, we are creating a volume of size 100MB and with a name of demo.
Output
The output of the above command is shown below −
Listing all the Volumes
You can also list all the docker volumes on a docker host. More details on this command is given below −
Syntax
docker volume ls
Options
None
Return Value
The command will output all the volumes on the docker host.
Example
sudo docker volume ls
Output
The output of the above command is shown below −
Docker - Networking
Docker takes care of the networking aspects so that the containers can communicate with other containers and also with the Docker Host. If you do an ifconfig on the Docker Host, you will see the Docker Ethernet adapter. This adapter is created when Docker is installed on the Docker Host.
This is a bridge between the Docker Host and the Linux Host. Now let’s look at some commands associated with networking in Docker.
Listing All Docker Networks
This command can be used to list all the networks associated with Docker on the host.
Syntax
docker network ls
Options
None
Return Value
The command will output all the networks on the Docker Host.
Example
sudo docker network ls
Output
The output of the above command is shown below
Inspecting a Docker network
If you want to see more details on the network associated with Docker, you can use the Docker network inspect command.
Syntax
docker network inspect networkname
Options
Return Value
The command will output all the details about the network.
Example
sudo docker network inspect bridge
Output
The output of the above command is shown below −
Now let’s run a container and see what happens when we inspect the network again. Let’s spin up an Ubuntu container with the following command −
sudo docker run –it ubuntu:latest /bin/bash
Now if we inspect our network name via the following command, you will now see that the container is attached to the bridge.
sudo docker network inspect bridge
Creating Your Own New Network
One can create a network in Docker before launching containers. This can be done with the following command −
Syntax
docker network create –-driver drivername name
Options
Return Value
The command will output the long ID for the new network.
Example
sudo docker network create –-driver bridge new_nw
Output
The output of the above command is shown below −
You can now attach the new network when launching the container. So let’s spin up an Ubuntu container with the following command −
sudo docker run –it –network=new_nw ubuntu:latest /bin/bash
And now when you inspect the network via the following command, you will see the container attached to the network.
sudo docker network inspect new_nw
Docker - Setting Node.js
Node.js is a JavaScript framework that is used for developing server-side applications. It is an open source framework that is developed to run on a variety of operating systems. Since Node.js is a popular framework for development, Docker has also ensured it has support for Node.js applications.
We will now see the various steps for getting the Docker container for Node.js up and running.
Step 1 − The first step is to pull the image from Docker Hub. When you log into Docker Hub, you will be able to search and see the image for Node.js as shown below. Just type in Node in the search box and click on the node (official) link which comes up in the search results.
Step 2 − You will see that the Docker pull command for node in the details of the repository in Docker Hub.
Step 3 − On the Docker Host, use the Docker pull command as shown above to download the latest node image from Docker Hub.
Once the pull is complete, we can then proceed with the next step.
Step 4 − On the Docker Host, let’s use the vim editor and create one Node.js example file. In this file, we will add a simple command to display “HelloWorld” to the command prompt.
In the Node.js file, let’s add the following statement −
Console.log(‘Hello World’);
This will output the “Hello World” phrase when we run it through Node.js.
Ensure that you save the file and then proceed to the next step.
Step 5 − To run our Node.js script using the Node Docker container, we need to execute the following statement −
sudo docker run –it –rm –name = HelloWorld –v “$PWD”:/usr/src/app
–w /usr/src/app node node HelloWorld.js
The following points need to be noted about the above command −
The –rm option is used to remove the container after it is run.
We are giving a name to the container called “HelloWorld”.
We are mentioning to map the volume in the container which is /usr/src/app to our current present working directory. This is done so that the node container will pick up our HelloWorld.js script which is present in our working directory on the Docker Host.
The –w option is used to specify the working directory used by Node.js.
The first node option is used to specify to run the node image.
The second node option is used to mention to run the node command in the node container.
And finally we mention the name of our script.
We will then get the following output. And from the output, we can clearly see that the Node container ran as a container and executed the HelloWorld.js script.
Docker - Setting MongoDB
MongoDB is a famous document-oriented database that is used by many modern-day web applications. Since MongoDB is a popular database for development, Docker has also ensured it has support for MongoDB.
We will now see the various steps for getting the Docker container for MongoDB up and running.
Step 1 − The first step is to pull the image from Docker Hub. When you log into Docker Hub, you will be able to search and see the image for Mongo as shown below. Just type in Mongo in the search box and click on the Mongo (official) link which comes up in the search results.
Step 2 − You will see that the Docker pull command for Mongo in the details of the repository in Docker Hub.
Step 3 − On the Docker Host, use the Docker pull command as shown above to download the latest Mongo image from Docker Hub.
Step 4 − Now that we have the image for Mongo, let’s first run a MongoDB container which will be our instance for MongoDB. For this, we will issue the following command −
sudo docker run -it -d mongo
The following points can be noted about the above command −
The –it option is used to run the container in interactive mode.
The –d option is used to run the container as a daemon process.
And finally we are creating a container from the Mongo image.
You can then issue the docker ps command to see the running containers −
Take a note of the following points −
The name of the container is tender_poitras. This name will be different since the name of the containers keep on changing when you spin up a container. But just make a note of the container which you have launched.
Next, also notice the port number it is running on. It is listening on the TCP port of 27017.
Step 5 − Now let’s spin up another container which will act as our client which will be used to connect to the MongoDB database. Let’s issue the following command for this −
sudo docker run –it –link=tender_poitras:mongo mongo /bin/bash
The following points can be noted about the above command −
The –it option is used to run the container in interactive mode.
We are now linking our new container to the already launched MongoDB server container. Here, you need to mention the name of the already launched container.
We are then specifying that we want to launch the Mongo container as our client and then run the bin/bash shell in our new container.
You will now be in the new container.
Step 6 − Run the env command in the new container to see the details of how to connect to the MongoDB server container.
Step 6 − Now it’s time to connect to the MongoDB server from the client container. We can do this via the following command −
mongo 172.17.0.2:27017
The following points need to be noted about the above command
Once you run the command, you will then be connected to the MongoDB database.
You can then run any MongoDB command in the command prompt. In our example, we are running the following command −
use demo
This command is a MongoDB command which is used to switch to a database name demo. If the database is not available, it will be created.
Now you have successfully created a client and server MongoDB container.
Docker - Setting NGINX
NGINX is a popular lightweight web application that is used for developing server-side applications. It is an open-source web server that is developed to run on a variety of operating systems. Since nginx is a popular web server for development, Docker has ensured that it has support for nginx.
We will now see the various steps for getting the Docker container for nginx up and running.
Step 1 − The first step is to pull the image from Docker Hub. When you log into Docker Hub, you will be able to search and see the image for nginx as shown below. Just type in nginx in the search box and click on the nginx (official) link which comes up in the search results.
Step 2 − You will see that the Docker pull command for nginx in the details of the repository in Docker Hub.
Step 3 − On the Docker Host, use the Docker pull command as shown above to download the latest nginx image from Docker Hub.
Step 4 − Now let’s run the nginx container via the following command.
sudo docker run –p 8080:80 –d nginx
We are exposing the port on the nginx server which is port 80 to the port 8080 on the Docker Host.
Once you run the command, you will get the following output if you browse to the URL http://dockerhost:8080. This shows that the nginx container is up and running.
Step 5 − Let’s look at another example where we can host a simple web page in our ngnix container. In our example, we will create a simple HelloWorld.html file and host it in our nginx container.
Let’s first create an HTML file called HelloWorld.html
Let’s add a simple line of Hello World in the HTML file.
Let’s then run the following Docker command.
sudo docker run –p 8080:80 –v
“$PWD”:/usr/share/nginx/html:ro –d nginx
The following points need to be noted about the above command −
We are exposing the port on the nginx server which is port 80 to the port 8080 on the Docker Host.
Next, we are attaching the volume on the container which is /usr/share/nginx/html to our present working directory. This is where our HelloWorld.html file is stored.
Now if we browse to the URL http://dockerhost:8080/HelloWorld.html we will get the following output as expected −
Docker - Toolbox
In the introductory chapters, we have seen the installation of Docker toolbox on Windows. The Docker toolbox is developed so that Docker containers can be run on Windows and MacOS. The site for toolbox on Windows is https://docs.docker.com/docker-for-windows/
For Windows, you need to have Windows 10 or Windows Server 2016 with Hyper-V enabled.
The toolbox consists of the following components −
Docker Engine − This is used as the base engine or Docker daemon that is used to run Docker containers.
Docker Machine − for running Docker machine commands.
Docker Compose for running Docker compose commands.
Kinematic − This is the Docker GUI built for Windows and Mac OS.
Oracle virtualbox
Let’s now discuss the different types of activities that are possible with Docker toolbox.
Running in Powershell
With Docker toolbox on Windows 10, you can now run Docker commands off powershell. If you open powershell on Windows and type in the command of Docker version, you will get all the required details about the Docker version installed.
Pulling Images and Running Containers
You can also now pull Images from Docker Hub and run containers in powershell as you would do in Linux. The following example will show in brief the downloading of the Ubuntu image and running of the container off the image.
The first step is to use the Docker pull command to pull the Ubuntu image from Docker Hub.
The next step is to run the Docker image using the following run command −
docker run –it ubuntu /bin/bash
You will notice that the command is the same as it was in Linux.
Kitematic
This is the GUI equivalent of Docker on Windows. To open this GUI, go to the taskbar and on the Docker icon, right-click and choose to open Kitematic.
It will prompt you to download Kitematic GUI. Once downloaded, just unzip the contents. There will be a file called Kitematic.exe. Double-click this exe file to open the GUI interface.
You will then be requested to log into Docker Hub, enter through the GUI. Just enter the required username and password and then click the Login button.
Once logged in, you will be able to see all the images downloaded on the system on the left-hand side of the interface.
On the right-hand side, you will find all the images available on Docker Hub.
Let’s take an example to understand how to download the Node image from Docker Hub using Kitematic.
Step 1 − Enter the keyword of node in the search criteria.
Step 2 − Click the create button on official Node image. You will then see the image being downloaded.
Once the image has been downloaded, it will then start running the Node container.
Step 3 − If you go to the settings tab, you can drill-down to further settings options, as shown below.
General settings − In this tab, you can name the container, change the path settings, and delete the container.
Docker - Setting ASP.Net
ASP.Net is the standard web development framework that is provided by Microsoft for developing server-side applications. Since ASP.Net has been around for quite a long time for development, Docker has ensured that it has support for ASP.Net.
In this chapter, we will see the various steps for getting the Docker container for ASP.Net up and running.
Prerequisites
The following steps need to be carried out first for running ASP.Net.
Step 1 − Since this can only run on Windows systems, you first need to ensure that you have either Windows 10 or Window Server 2016.
Step 2 − Next, ensure that Hyper-V is and Containers are installed on the Windows system. To install Hyper–V and Containers, you can go to Turn Windows Features ON or OFF. Then ensure the Hyper-V option and Containers is checked and click the OK button.
The system might require a restart after this operation.
Step 3 − Next, you need to use the following Powershell command to install the 1.13.0rc4 version of Docker. The following command will download this and store it in the temp location.
Invoke-WebRequest "https://test.docker.com/builds/Windows/x86_64/docker-1.13.0-
rc4.zip" -OutFile "$env:TEMP\docker-1.13.0-rc4.zip" –UseBasicParsing
Step 4 − Next, you need to expand the archive using the following powershell command.
Expand-Archive -Path "$env:TEMP\docker-1.13.0-rc4.zip" -DestinationPath $env:ProgramFiles
Step 5 − Next, you need to add the Docker Files to the environment variable using the following powershell command.
$env:path += ";$env:ProgramFiles\Docker"
Step 6 − Next, you need to register the Docker Daemon Service using the following powershell command.
dockerd --register-service
Step 7 − Finally, you can start the docker daemon using the following command.
Start-Service Docker
Use the docker version command in powershell to verify that the docker daemon is working
Installing the ASP.Net Container
Let’s see how to install the ASP.Net container.
Step 1 − The first step is to pull the image from Docker Hub. When you log into Docker Hub, you will be able to search and see the image for Microsoft/aspnet as shown below. Just type in asp in the search box and click on the Microsoft/aspnet link which comes up in the search results.
Step 2 − You will see that the Docker pull command for ASP.Net in the details of the repository in Docker Hub.
Step 3 − Go to Docker Host and run the Docker pull command for the microsoft/aspnet image. Note that the image is pretty large, somewhere close to 4.2 GB.
Step 4 − Now go to the following location https://github.com/Microsoft/aspnet-docker and download the entire Git repository.
Step 5 − Create a folder called App in your C drive. Then copy the contents from the 4.6.2/sample folder to your C drive. Go the Docker File in the sample directory and issue the following command −
docker build –t aspnet-site-new –build-arg site_root=/
The following points need to be noted about the above command −
- It builds a new image called aspnet-site-new from the Docker File.
- The root path is set to the localpath folder.
Step 6 − Now it’s time to run the container. It can be done using the following command −
docker run –d –p 8000:80 –name my-running-site-new aspnet-site-new
Step 7 − You will now have IIS running in the Docker container. To find the IP Address of the Docker container, you can issue the Docker inspect command as shown below.
Docker - Cloud
The Docker Cloud is a service provided by Docker in which you can carry out the following operations −
Nodes − You can connect the Docker Cloud to your existing cloud providers such as Azure and AWS to spin up containers on these environments.
Cloud Repository − Provides a place where you can store your own repositories.
Continuous Integration − Connect with Github and build a continuous integration pipeline.
Application Deployment − Deploy and scale infrastructure and containers.
Continuous Deployment − Can automate deployments.
Getting started
You can go to the following link to getting started with Docker Cloud − https://cloud.docker.com/
Once logged in, you will be provided with the following basic interface −
Connecting to the Cloud Provider
The first step is to connect to an existing cloud provider. The following steps will show you how to connect with an Amazon Cloud provider.
Step 1 − The first step is to ensure that you have the right AWS keys. This can be taken from the aws console. Log into your aws account using the following link − https://aws.amazon.com/console/
Step 2 − Once logged in, go to the Security Credentials section. Make a note of the access keys which will be used from Docker Hub.
Step 3 − Next, you need to create a policy in aws that will allow Docker to view EC2 instances. Go to the profiles section in aws. Click the Create Policy button.
Step 4 − Click on ‘Create Your Own Policy’ and give the policy name as dockercloudpolicy and the policy definition as shown below.
{
"Version": "2012-10-17",
"Statement": [ {
"Action": [
"ec2:*",
"iam:ListInstanceProfiles"
],
"Effect": "Allow",
"Resource": "*"
} ]
}
Next, click the Create Policy button
Step 5 − Next, you need to create a role which will be used by Docker to spin up nodes on AWS. For this, go to the Roles section in AWS and click the Create New Role option.
Step 6 − Give the name for the role as dockercloud-role.
Step 7 − On the next screen, go to ‘Role for Cross Account Access’ and select “Provide access between your account and a 3rd party AWS account".
Step 8 − On the next screen, enter the following details −
- In the Account ID field, enter the ID for the Docker Cloud service: 689684103426.
- In the External ID field, enter your Docker Cloud username.
Step 9 − Then, click the Next Step button and on the next screen, attach the policy which was created in the earlier step.
Step 10 − Finally, on the last screen when the role is created, make sure to copy the arn role which is created.
arn:aws:iam::085363624145:role/dockercloud-role
Step 11 − Now go back to Docker Cloud, select Cloud Providers, and click the plug symbol next to Amazon Web Services.
Enter the arn role and click the Save button.
Once saved, the integration with AWS would be complete.
Setting Up Nodes
Once the integration with AWS is complete, the next step is to setup a node. Go to the Nodes section in Docker Cloud. Note that the setting up of nodes will automatically setup a node cluster first.
Step 1 − Go to the Nodes section in Docker Cloud.
Step 2 − Next, you can give the details of the nodes which will be setup in AWS.
You can then click the Launch Node cluster which will be present at the bottom of the screen. Once the node is deployed, you will get the notification in the Node Cluster screen.
Deploying a Service
The next step after deploying a node is to deploy a service. To do this, we need to perform the following steps.
Step 1 − Go to the Services Section in Docker Cloud. Click the Create button
Step 2 − Choose the Service which is required. In our case, let’s choose mongo.
Step 3 − On the next screen, choose the Create & Deploy option. This will start deploying the Mongo container on your node cluster.
Once deployed, you will be able to see the container in a running state.
Docker - Logging
Docker has logging mechanisms in place which can be used to debug issues as and when they occur. There is logging at the daemon level and at the container level. Let’s look at the different levels of logging.
Daemon Logging
At the daemon logging level, there are four levels of logging available −
Debug − It details all the possible information handled by the daemon process.
Info − It details all the errors + Information handled by the daemon process.
Errors − It details all the errors handled by the daemon process.
Fatal − It only details all the fatal errors handled by the daemon process.
Go through the following steps to learn how to enable logging.
Step 1 − First, we need to stop the docker daemon process, if it is already running. It can be done using the following command −
sudo service docker stop
Step 2 − Now we need to start the docker daemon process. But this time, we need to append the –l parameter to specify the logging option. So let’s issue the following command when starting the docker daemon process.
sudo dockerd –l debug &
The following points need to be noted about the above command −
dockerd is the executable for the docker daemon process.
The –l option is used to specify the logging level. In our case, we are putting this as debug
& is used to come back to the command prompt after the logging has been enabled.
Once you start the Docker process with logging, you will also now see the Debug Logs being sent to the console.
Now, if you execute any Docker command such as docker images, the Debug information will also be sent to the console.
Container Logging
Logging is also available at the container level. So in our example, let’s spin up an Ubuntu container first. We can do it by using the following command.
sudo docker run –it ubuntu /bin/bash
Now, we can use the docker log command to see the logs of the container.
Syntax
Docker logs containerID
Parameters
Example
On our Docker Host, let’s issue the following command. Before that, you can issue some commands whilst in the container.
sudo docker logs 6bfb1271fcdd
Output
From the output, you can see that the commands executed in the container are shown in the logs.
Docker - Compose
Docker Compose is used to run multiple containers as a single service. For example, suppose you had an application which required NGNIX and MySQL, you could create one file which would start both the containers as a service without the need to start each one separately.
In this chapter, we will see how to get started with Docker Compose. Then, we will look at how to get a simple service with MySQL and NGNIX up and running using Docker Compose.
Docker Compose ─ Installation
The following steps need to be followed to get Docker Compose up and running.
Step 1 − Download the necessary files from github using the following command −
curl -L "https://github.com/docker/compose/releases/download/1.10.0-rc2/dockercompose
-$(uname -s) -$(uname -m)" -o /home/demo/docker-compose
The above command will download the latest version of Docker Compose which at the time of writing this article is 1.10.0-rc2. It will then store it in the directory /home/demo/.
Step 2 − Next, we need to provide execute privileges to the downloaded Docker Compose file, using the following command −
chmod +x /home/demo/docker-compose
We can then use the following command to see the compose version.
Syntax
docker-compose version
Parameters
Output
The version details of Docker Compose will be displayed.
Example
The following example shows how to get the docker-compose version.
sudo ./docker-compose -version
Output
You will then get the following output −
Creating Your First Docker-Compose File
Now let’s go ahead and create our first Docker Compose file. All Docker Compose files are YAML files. You can create one using the vim editor. So execute the following command to create the compose file −
sudo vim docker-compose.yml
Let’s take a close look at the various details of this file −
The database and web keyword are used to define two separate services. One will be running our mysql database and the other will be our nginx web server.
The image keyword is used to specify the image from dockerhub for our mysql and nginx containers
For the database, we are using the ports keyword to mention the ports that need to be exposed for mysql.
And then, we also specify the environment variables for mysql which are required to run mysql.
Now let’s run our Docker Compose file using the following command −
sudo ./docker-compose up
This command will take the docker-compose.yml file in your local directory and start building the containers.
Once executed, all the images will start downloading and the containers will start automatically.
And when you do a docker ps, you can see that the containers are indeed up and running.
Docker - Continuous Integration
Docker has integrations with many Continuous Integrations tools, which also includes the popular CI tool known as Jenkins. Within Jenkins, you have plugins available which can be used to work with containers. So let’s quickly look at a Docker plugin available for the Jenkins tool.
Let’s go step by step and see what’s available in Jenkins for Docker containers.
Step 1 − Go to your Jenkins dashboard and click Manage Jenkins.
Step 2 − Go to Manage Plugins.
Step 3 − Search for Docker plugins. Choose the Docker plugin and click the Install without restart button.
Step 4 − Once the installation is completed, go to your job in the Jenkins dashboard. In our example, we have a job called Demo.
Step 5 − In the job, when you go to the Build step, you can now see the option to start and stop containers.
Step 6 − As a simple example, you can choose the further option to stop containers when the build is completed. Then, click the Save button.
Now, just run your job in Jenkins. In the Console output, you will now be able to see that the command to Stop All containers has run.
Docker - Kubernetes Architecture
Kubernetes is an orchestration framework for Docker containers which helps expose containers as services to the outside world. For example, you can have two services − One service would contain nginx and mongoDB, and another service would contain nginx and redis. Each service can have an IP or service point which can be connected by other applications. Kubernetes is then used to manage these services.
The following diagram shows in a simplistic format how Kubernetes works from an architecture point of view.
The minion is the node on which all the services run. You can have many minions running at one point in time. Each minion will host one or more POD. Each POD is like hosting a service. Each POD then contains the Docker containers. Each POD can host a different set of Docker containers. The proxy is then used to control the exposing of these services to the outside world.
Kubernetes has several components in its architecture. The role of each component is explained below &mius;
etcd − This component is a highly available key-value store that is used for storing shared configuration and service discovery. Here the various applications will be able to connect to the services via the discovery service.
Flannel − This is a backend network which is required for the containers.
kube-apiserver − This is an API which can be used to orchestrate the Docker containers.
kube-controller-manager − This is used to control the Kubernetes services.
kube-scheduler − This is used to schedule the containers on hosts.
Kubelet − This is used to control the launching of containers via manifest files.
kube-proxy − This is used to provide network proxy services to the outside world.
Docker - Working of Kubernetes
In this chapter, we will see how to install Kubenetes via kubeadm. This is a tool which helps in the installation of Kubernetes. Let’s go step by step and learn how to install Kubernetes.
Step 1 − Ensure that the Ubuntu server version you are working on is 16.04.
Step 2 − Ensure that you generate a ssh key which can be used for ssh login. You can do this using the following command.
ssh-keygen
This will generate a key in your home folder as shown below.
Step 3 − Next, depending on the version of Ubuntu you have, you will need to add the relevant site to the docker.list for the apt package manager, so that it will be able to detect the Kubernetes packages from the kubernetes site and download them accordingly.
We can do it using the following commands.
curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | apt-key add -
echo "deb http://apt.kubernetes.io/ kubernetes-xenial main” | sudo tee /etc/apt/sources.list.d/docker.list
Step 4 − We then issue an apt-get update to ensure all packages are downloaded on the Ubuntu server.
Step 5 − Install the Docker package as detailed in the earlier chapters.
Step 6 − Now it’s time to install kubernetes by installing the following packages −
apt-get install –y kubelet kubeadm kubectl kubernetes-cni
Step 7 − Once all kubernetes packages are downloaded, it’s time to start the kubernetes controller using the following command −
kubeadm init
Once done, you will get a successful message that the master is up and running and nodes can now join the cluster.
