Targeting minions is specifying which minions should run a command or execute a state by matching against hostnames, or system information, or defined groups, or even combinations thereof.
For example the command
salt web1 apache.signal restart to restart the
Apache httpd server specifies the machine
web1 as the target and the
command will only be run on that one minion.
Similarly when using States, the following top file specifies that only
web1 minion should execute the contents of
base: 'web1': - webserver
The simple target specifications, glob, regex, and list will cover many use cases, and for some will cover all use cases, but more powerful options exist.
The Grains interface was built into Salt to allow minions to be targeted by system properties. So minions running on a particular operating system can be called to execute a function, or a specific kernel.
Calling via a grain is done by passing the -G option to salt, specifying a grain and a glob expression to match the value of the grain. The syntax for the target is the grain key followed by a globexpression: "os:Arch*".
salt -G 'os:Fedora' test.ping
Will return True from all of the minions running Fedora.
To discover what grains are available and what the values are, execute the grains.item salt function:
salt '*' grains.items
more info on using targeting with grains can be found here.
As of 0.8.8 targeting with executions is still under heavy development and this documentation is written to reference the behavior of execution matching in the future.
Execution matching allows for a primary function to be executed, and then based on the return of the primary function the main function is executed.
Execution matching allows for matching minions based on any arbitrary running data on the minions.
Multiple target interfaces can be used in conjunction to determine the command targets. These targets can then be combined using and or or statements. This is well defined with an example:
salt -C 'G@os:Debian and webser* or E@db.*' test.ping
In this example any minion who's id starts with
webser and is running
Debian, or any minion who's id starts with db will be matched.
The type of matcher defaults to glob, but can be specified with the
corresponding letter followed by the
@ symbol. In the above example a grain
is used with
G@ as well as a regular expression with
webser* target does not need to be prefaced with a target type specifier
because it is a glob.
more info on using compound targeting can be found here.
For certain cases, it can be convenient to have a predefined group of minions on which to execute commands. This can be accomplished using what are called nodegroups. Nodegroups allow for predefined compound targets to be declared in the master configuration file, as a sort of shorthand for having to type out complicated compound expressions.
nodegroups: group1: 'L@foo.domain.com,bar.domain.com,baz.domain.com and bl*.domain.com' group2: 'G@os:Debian and foo.domain.com' group3: 'G@os:Debian and N@group1'
There are many ways to target individual minions or groups of minions in Salt: