Ansible ships with a number of modules that can be executed directly on remote hosts or through ansible playbooks.
Nearly all modules take key=value parameters, space delimited. Some modules take no parameters, and the command/shell modules simply take the string of the command you want to run.
All modules return JSON format data, though if you are using the command line or playbooks, you don’t really need to know much about that.
Most modules other than command are idempotent, meaning they will seek to avoid changes unless a change needs to be made. When using ansible playbooks, these modules can trigger change events. Unless otherwise noted, all modules support change hooks.
Stock modules:
The command module takes the command name followed by a list of arguments, space delimited.
If you want to run a command through the shell (say you are using ‘<’, ‘>’, ‘|’, etc), you actually want the ‘shell’ module instead. The ‘command’ module is much more secure as it’s not affected by the user’s environment.
Example usage:
/sbin/shutdown -t now
The given command will be executed on all selected nodes. It will not be processed through the shell, so variables like “$HOME” and operations like “<”, “>”, “|”, and “&” will not work. As such, all paths to commands must be fully qualified.
This module does not support change hooks and returns the return code from the program as well as timing information about how long the command was running for.
The copy module moves a file on the local box to remote locations. In addition to the options listed below, the arguments available to the file module can also be passed to the copy module.
src:
dest:
This module also returns md5sum information about the resultant file.
Runs the discovery program ‘facter’ on the remote system, returning JSON data that can be useful for inventory purposes.
Requires that ‘facter’ and ‘ruby-json’ be installed on the remote end.
This module is informative only - it takes no parameters & does not support change hooks, nor does it make any changes on the system. Playbooks do not actually use this module, they use the setup module behind the scenes.
Sets attributes of files and directories, or removes files/directories. All parameters available to the file module are also available when running the copy or template modules.
dest:
state:
mode:
owner:
group:
Deploys software (or files) from git checkouts.
repo:
dest:
version:
Similar to the facter module, this returns JSON inventory data. Ohai data is a bit more verbose and nested than facter.
Requires that ‘ohai’ be installed on the remote end.
This module is information only - it takes no parameters & does not support change hooks, nor does it make any changes on the system.
Playbooks should not call the ohai module, playbooks call the setup module behind the scenes instead.
A trivial test module, this module always returns the integer 1 on successful contact.
This module does not support change hooks and is informative only - it takes no parameters & does not support change hooks, nor does it make any changes on the system.
Controls services on remote machines.
state:
name:
Writes a JSON file containing key/value data, for use in templating. Call this once before using the template module. Playbooks will execute this module automatically as the first step in each play using the variables section, so it is unnecessary to make explicit calls to setup within a playbook.
If facter or ohai are installed, variables from these programs will also be snapshotted into the JSON file for usage in templating. These variables are prefixed with facter_ and ohai_ so it’s easy to tell their source. All variables are then bubbled up to the caller.
anything:
- Any other parameters can be named basically anything, and set a key=value pair in the JSON file for use in templating.
The shell module takes the command name followed by a list of arguments, space delimited. It is almost exactly like the command module but runs the command through the shell rather than directly.
Example usage:
find . | grep *.txt
The given command will be executed on all selected nodes.
If you want to execute a command securely and predicably, it may be better to use the ‘command’ module instead. Best practices when writing playbooks will follow the trend of using ‘command’ unless ‘shell’ is explicitly required. When running ad-hoc commands, use your best judgement.
This module does not support change hooks and returns the return code from the program as well as timing information about how long the command was running for.
Templates a file out to a remote server. Call the setup module prior to usage if you are not running from a playbook. In addition to the options listed below, the arguments available to the file module can also be passed to the copy module.
src:
dest:
This module also returns md5sum information about the resultant file.
Will install, upgrade, remove, and list packages with the yum package manager.
pkg:
state:
list:
To write your own modules, simply follow the convention of those already available in /usr/share/ansible. Modules must return JSON but can be written in any language. Modules should return hashes, but hashes can be nested.
To support change hooks, modules should return hashes with a changed: True/False element at the top level:
{
'changed' : True,
'something' : 42
}
Modules can also choose to indicate a failure scenario by returning a top level failure element with a True value, and a msg element describing the nature of the failure. Other return values are up to the module:
{
'failure' : True,
'msg' : "here is what happened..."
}
When shipping modules, drop them in /usr/share/ansible, or specify the module path to the command line tool or API. It is easy to test modules by running them directly on the command line, passing them arguments just like they would be passed with ansible.
See also