SaltStack - Remote Execution
One of the core concepts of Salt is remote execution. Salt can execute commands across thousands of systems in a matter of seconds. Salt uses its own command to do this functionality. Let us now understand the different Salt commands for remote execution in the chapter.
Salt Command
Salt command enables the Salt master to communicate with one or more Salt minions. The basic syntax is as follows,
salt '<target>' <module.function> [arguments]
The above command syntax consists of the following three main components.
target − It determines which systems is applied by the command.
module.function − It is a command. Commands consists of a module and function.
arguments − Additional data needed for calling the function.
Let us understand each of the components in detail.
What is the Target Component?
Target is a component, which allows you to filter minions (managed system) to run the function. A simple command using the target component is defined below.
salt '*' test.ping
It will produce the following output −
minion2:
True
minion1:
True
Here, the target ‘*’ represents all the managed systems. The ‘test’ here is a module and ping is a function. This is used to test the ping service in the remote system. We will learn about the different modules and its functions in subsequent chapters.
Targets using ID (minion)
You can send a command to a specific minion using its id in the target. Instead of using '*', you can replace it using minion id. It is defined below.
salt 'minion1’ test.ping
It will produce the following output −
minion1:
True
Targets using Regular Expression
Targets can be filtered by specific regular expression. It is defined below.
salt -E 'minion[0-9]' test.ping
It will produce the following output −
minion2:
True
minion1:
True
Targets using List
Targets can be explicitly specified in a list. It is defined in the following code block.
salt -L 'minion1,minion2' test.ping
It will produce the following output −
minion2:
True
minion1:
True
Targets by Condition
Targets can be combined in one command as shown in the code block below.
salt -C 'G@os:Ubuntu and minion* or S@192.168.50.*' test.ping
It will produce the following output −
minion1:
True
minion2:
True
Module and Functions (module.function)
Salt can execute shell commands; update packages and distribute files, etc., in all of its managed systems simultaneously. Salt does these operations using modules. Salt has special modules for all the available functionalities. Let us understand the different Salt modules using some simple example in this chapter.
Shell Command
Salt executes shell commands remotely across multiple systems using the cmd.run command. The cmd is the main module and run is one of the function available in the cmd module. The run function enables any shell command to be executed in the remote system as shown in the code block below.
salt '*' cmd.run 'ls -l /etc'
It will produce the following output −
minion2:
total 868
drwxr-xr-x 7 root root 4096 Jan 26 22:10 X11
drwxr-xr-x 3 root root 4096 Jan 26 21:02 acpi
-rw-r--r-- 1 root root 2981 Jan 26 20:48 adduser.conf
-rw-r--r-- 1 root root 10 Jan 26 21:04 adjtime
drwxr-xr-x 2 root root 4096 Jan 26 22:10 alternatives
drwxr-xr-x 3 root root 4096 Jan 26 20:53 apm
drwxr-xr-x 3 root root 4096 Jan 26 21:02 apparmor
drwxr-xr-x 9 root root 4096 Jan 26 21:02 apparmor.d
drwxr-xr-x 3 root root 4096 Jan 26 21:02 apport
drwxr-xr-x 6 root root 4096 Jan 29 07:14 apt
drwxr-xr-x 2 root root 4096 Jan 26 22:10 at-spi2
……………
……………
minion1:
total 868
drwxr-xr-x 7 root root 4096 Jan 26 22:10 X11
drwxr-xr-x 3 root root 4096 Jan 26 21:02 acpi
-rw-r--r-- 1 root root 2981 Jan 26 20:48 adduser.conf
-rw-r--r-- 1 root root 10 Jan 26 21:04 adjtime
drwxr-xr-x 2 root root 4096 Jan 26 22:10 alternatives
drwxr-xr-x 3 root root 4096 Jan 26 20:53 apm
drwxr-xr-x 3 root root 4096 Jan 26 21:02 apparmor
drwxr-xr-x 9 root root 4096 Jan 26 21:02 apparmor.d
drwxr-xr-x 3 root root 4096 Jan 26 21:02 apport
drwxr-xr-x 6 root root 4096 Jan 29 07:09 apt
drwxr-xr-x 2 root root 4096 Jan 26 22:10 at-spi2
-rw-r----- 1 root daemon 144 Oct 21 2013 at.deny
-rw-r--r-- 1 root root 2177 Apr 9 2014 bash.bashrc
-rw-r--r-- 1 root root 45 Mar 22 2014 bash_completion
……………
……………
Show Disk Usage
Salt provides a special module, disk to get the complete disk details of the managed system. The diskmodule has a usage function to query the details.
salt '*' disk.usage
It will produce the following output −
minion1:
----------
/:
----------
1K-blocks:
41251136
available:
37852804
capacity:
5%
filesystem:
/dev/sda1
used:
1662420
/dev:
----------
1K-blocks:
503908
available:
503896
capacity:
1%
filesystem:
udev
used:
12
/run:
----------
1K-blocks:
101780
available:
101412
capacity:
1%
filesystem:
tmpfs
used:
368
/run/lock:
----------
1K-blocks:
5120
available:
5120
capacity:
0%
filesystem:
none
used:
0
/run/shm:
----------
1K-blocks:
508884
available:
508872
capacity:
1%
filesystem:
none
used:
12
/run/user:
----------
1K-blocks:
102400
available:
102400
capacity:
0%
filesystem:
none
used:
0
/sys/fs/cgroup:
----------
1K-blocks:
4
available:
4
capacity:
0%
filesystem:
none
used:
0
/vagrant:
----------
1K-blocks:
303114632
available:
252331440
capacity:
17%
filesystem:
none
used:
50783192
minion2:
----------
/:
----------
1K-blocks:
41251136
available:
37852804
capacity:
5%
filesystem:
/dev/sda1
used:
1662420
/dev:
----------
1K-blocks:
503908
available:
503896
capacity:
1%
filesystem:
udev
used:
12
/run:
----------
1K-blocks:
101780
available:
101412
capacity:
1%
filesystem:
tmpfs
used:
368
/run/lock:
----------
1K-blocks:
5120
available:
5120
capacity:
0%
filesystem:
none
used:
0
/run/shm:
----------
1K-blocks:
508884
available:
508872
capacity:
1%
filesystem:
none
used:
12
/run/user:
----------
1K-blocks:
102400
available:
102400
capacity:
0%
filesystem:
none
used:
0
/sys/fs/cgroup:
----------
1K-blocks:
4
available:
4
capacity:
0%
filesystem:
none
used:
0
/vagrant:
----------
1K-blocks:
303114632
available:
252331440
capacity:
17%
filesystem:
none
used:
50783192
Network Interfaces
Salt provides a separate module, network and function, interfaces inside the module to query the network interface information about the managed systems.
salt '*' network.interfaces
It will produce the following output −
minion1:
----------
eth0:
----------
hwaddr:
08:00:27:04:3e:28
inet:
|_
----------
address:
10.0.2.15
broadcast:
10.0.2.255
label:
eth0
netmask:
255.255.255.0
inet6:
|_
----------
address:
fe80::a00:27ff:fe04:3e28
prefixlen:
64
scope:
link
up:
True
eth1:
----------
hwaddr:
08:00:27:34:10:52
inet:
|_
----------
address:
192.168.50.11
broadcast:
192.168.50.255
label:
eth1
netmask:
255.255.255.0
inet6:
|_
----------
address:
fe80::a00:27ff:fe34:1052
prefixlen:
64
scope:
link
up:
True
lo:
----------
hwaddr:
00:00:00:00:00:00
inet:
|_
----------
address:
127.0.0.1
broadcast:
None
label:
lo
netmask:
255.0.0.0
inet6:
|_
----------
address:
::1
prefixlen:
128
scope:
host
up:
True
minion2:
----------
eth0:
----------
hwaddr:
08:00:27:04:3e:28
inet:
|_
----------
address:
10.0.2.15
broadcast:
10.0.2.255
label:
eth0
netmask:
255.255.255.0
inet6:
|_
----------
address:
fe80::a00:27ff:fe04:3e28
prefixlen:
64
scope:
link
up:
True
eth1:
----------
hwaddr:
08:00:27:a7:31:8e
inet:
|_
----------
address:
192.168.50.12
broadcast:
192.168.50.255
label:
eth1
netmask:
255.255.255.0
inet6:
|_
----------
address:
fe80::a00:27ff:fea7:318e
prefixlen:
64
scope:
link
up:
True
lo:
----------
hwaddr:
00:00:00:00:00:00
inet:
|_
----------
address:
127.0.0.1
broadcast:
None
label:
lo
netmask:
255.0.0.0
inet6:
|_
----------
address:
::1
prefixlen:
128
scope:
host
up:
True
sys.doc Execution Module
Salt functions can be sent to the sys.doc execution module. This is used to get the details on any module directly from the command line. The Salt functions are self-documenting. All the function documentation can be retrieved from the minions via the sys.doc() function, which is defined below.
salt '*' sys.doc
Arguments for a Function Call
Arguments are used to provide additional data for the function call. A simple argument example is given below.
salt '*' sys.doc pkg.install
Here, the argument pkg.install is a module to install specific packages.
Python Function
Arguments are space-delimited parameters to the function. It allows the python code to be passed as arguments as given below.
salt '*' cmd.exec_code python 'import sys;print sys.version'
It will produce the following output −
minion2:
2.7.6 (default, Oct 26 2016, 20:30:19)
[GCC 4.8.4]
minion1:
2.7.6 (default, Oct 26 2016, 20:30:19)
[GCC 4.8.4]
Similarly, you can use optional keywords and the YAML format as well.
