Ansible Modules¶

Ansible ships with a number of modules (called the ‘module library’) that can be executed directly on remote hosts or through Playbooks. Users can also write their own modules. These modules can control system resources, like services, packages, or files (anything really), or handle executing system commands.

Let’s review how we execute three different modules from the command line:

ansible webservers -m service -a "name=httpd state=running"
ansible webservers -m ping
ansible webservers -m command -a "/sbin/reboot -t now"

Each module supports taking arguments. Nearly all modules take key=value arguments, space delimited. Some modules take no arguments, and the command/shell modules simply take the string of the command you want to run.

From playbooks, Ansible modules are executed in a very similar way:

- name: reboot the servers
  action: command /sbin/reboot -t now

All modules technically return JSON format data, though if you are using the command line or playbooks, you don’t really need to know much about that. If you’re writing your own module, you care, and this means you do not have to write modules in any particular language – you get tho choose.

Most modules other than command are idempotent, meaning they will seek to avoid changes to the system unless a change needs to be made. When using Ansible playbooks, these modules can trigger ‘change events’. Unless otherwise noted, any given module does support change hooks.

Let’s see what’s available in the Ansible module library, out of the box:

apt¶

Manages apt-packages (such as for Debian/Ubuntu).

pkg:

A package name or package specifier with version, like name-1.0

state:

Can be either ‘installed’, ‘removed’, or ‘latest’. The default is ‘installed’.

update-cache:

Whether apt cache must be updated prior operation. Optional, and can be ‘yes’, or ‘no’. The default is ‘no’. This can be done as the part of a package operation or as a seperate step.

purge:

Will force purge of configuration file for when ensure is set to ‘removed’. Defaults to ‘no’.

Example action from Ansible Playbooks:

apt pkg=foo update-cache=yes
apt pkg=foo ensure=removed
apt pkg=foo ensure=installed
apt pkg=foo ensure=latest update-cache=yes

NOTE: the apt module cannot currently request installation of a specific software version, as the yum module can. This should be available in a future release.

command¶

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.

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.

Example action from Ansible Playbooks:

command /sbin/shutdown -t now

If you only want to run a command if a certain file does not exist, you can do the following:

command /usr/bin/make_database.sh arg1 arg2 creates=/path/to/database

The creates= option will not be passed to the executable.

copy¶

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:

Local path to a file to copy to the remote server. This can be an absolute or relative path.

dest:

Remote absolute path where the file should end up.

This module also returns md5sum information about the resultant file.

Example action from Ansible Playbooks:

copy src=/srv/myfiles/foo.conf dest=/etc/foo.conf owner=foo group=foo mode=0644

facter¶

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.

fetch¶

This module works like ‘copy’, but in reverse. It is used for fetching files from remote machines and storing them locally in a file tree, organized by hostname.

src:

The file on the remote system to fetch. This needs to be a file, not a directory. Recursive fetching may be supported later.

dest:

A directory to save the file into. For example, if the ‘dest’ directory is ‘/foo’, a src file named ‘/tmp/bar’ on host ‘host.example.com’, would be saved into ‘/foo/host.example.com/tmp/bar’ (in Ansible 0.0.3 and later).

The fetch module is a useful way to gather log files from remote systems. If you require fetching multiple files from remote systems, you may wish to execute a tar command and then fetch the tarball.

Example:

fetch src=/var/log/messages dest=/home/logtree

file¶

Sets attributes of files, symlinks, and directories, or removes files/symlinks/directories. All parameters available to the file module are also available when running the copy or template modules.

dest:

absolute path to a file on the filesystem.

state:

either ‘file’, ‘link’, ‘directory’, or ‘absent’. The default is ‘file’. If ‘directory’, the directory and all immediate subdirectories will be created if they do not exist. If ‘file’, the file will NOT be created if it does not exist, specify copy or template for the module name instead if you need to put content at the specified location. If ‘link’, the symbolic link will be created or changed. If ‘absent’, directories will be recursively deleted, and files or symlinks will be unlinked.

mode:

the mode the file or directory should be, such as 644, as would be given to chmod. English modes like “g+x” are not yet supported.

owner:

name of user that should own the file or directory, as would be given to chown.

group:

name of group that should own the file or directory, as would be given to chgrp

src:

path of the file to link to (applies only to ‘link’ state)

dest:

location where the symlink will be created for ‘link’ state, also an alias for ‘path’.

seuser:

‘user’ part of SELinux file context. Will default to what is provided by system policy, if available. Only used on systems with SELinux present.

serole:

‘role’ part of SELinux file context. Will default to what is provided by system policy, if available. Only used on systems with SELinux present.

setype:

‘type’ part of SELinux file context. Will default to what is provided by system policy, if available. Only used on systems with SELinux present.

selevel:

‘level’ part of SELinux file context. This is the MLS and MCS attribute of the file context. It defaults to ‘s0’. Only used only used on hosts with SELinux present.

context:

accepts only ‘default’ as value. This will restore a file’s selinux context to the default context in the policy. Does nothing if no default is available.

Example action from Ansible Playbooks:

file path=/etc/foo.conf owner=foo group=foo mode=0644
file path=/some/path owner=foo group=foo state=directory
file path=/path/to/delete state=absent
file src=/file/to/link/to dest=/path/to/symlink owner=foo group=foo state=link
file path=/some/path state=directory setype=httpd_sys_content_t
file path=/some/path state=directory context=default

git¶

Deploys software (or files) from git checkouts.

repo:

git or http protocol address of the repo to checkout.

dest:

Where to check it out, an absolute directory path.

version:

What version to check out – either the git SHA, the literal string HEAD, or a tag name.

Example action from Ansible Playbooks:

git repo=git://foosball.example.org/path/to/repo.git dest=/srv/checkout version=release-0.22

group¶

Adds or removes groups.

name:

name of the group

gid:

optional gid to set for the group

state:

either ‘absent’, or ‘present’. ‘present’ is the default.

To control members of the group, see the users resource.

Example action from Ansible Playbooks:

group name=somegroup state=present

ohai¶

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.

ping¶

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.

service¶

Controls services on remote machines.

state:

Values are started, stopped, or restarted. Started/stopped are idempotent actions that will not run commands unless necessary. restarted will always bounce the service.

name:

The name of the service.

Example action from Ansible Playbooks:

service name=httpd state=started
service name=httpd state=stopped
service name=httpd state=restarted

setup¶

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. Ansible also provides it’s own ‘facts’ about the remote system, which are prefixed with ansible_. All variables are then bubbled up to the caller. Using the ansible facts and chosing to not install facter and ohai means you can avoid ruby-dependencies on your remote systems.

anything:

Any other parameters can be named basically anything, and set a key=value pair in the JSON file for use in templating.

Example action from Ansible Playbooks:

vars:
    ntpserver: 'ntp.example.com'
    xyz: 1234

Example action from /usr/bin/ansible:

ansible all -m setup -a "ntpserver=ntp.example.com xyz=1234"

shell¶

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.

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.

Example action from a playbook:

shell somescript.sh >> somelog.txt

template¶

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:

Path of a Jinja2 formatted template on the local server. This can be a relative or absolute path.

dest:

Location to render the template on the remote server.

This module also returns md5sum information about the resultant file.

Example action from a playbook:

template src=/srv/mytemplates/foo.j2 dest=/etc/foo.conf owner=foo group=foo mode=0644

user¶

Creates user accounts, manipulates existing user accounts, and removes user accounts.

name:

Name of the user to create, remove, or edit

comment:

Optionally sets the description of the user

group:

Optionally sets the user’s primary group, takes a group name.

groups:

Put the user in the specified groups, takes comma delimited group names.

append:

If true, will only add additional groups to the user listed in ‘groups’, rather than making the user only be in those specified groups.

shell:

Optionally sets the user’s shell.

createhome:

Whether to create the user’s home directory. Takes ‘yes’, or ‘no’. The default is ‘yes’.

password:

Sets the user’s password to this crypted value. Pass in a result from crypt. See the users example in the github examples directory for what this looks like in a playbook.

state:

Defaults to ‘present’. When ‘absent’, the user account will be removed if present. Optionally additional removal behaviors can be set with the ‘force’ or ‘remove’ parameter values (see below).

force:

When used with a state of ‘absent’, the behavior denoted in the ‘userdel’ manpage for –force is also used when removing the user. Value is ‘yes’ or ‘no’, default is ‘no’.

remove:

When used with a state of ‘absent’, the behavior denoted in the ‘userdel’ manpage for –remove is also used when removing the user. Value is ‘yes’ or ‘no’, default is ‘no’.

Example action from Ansible Playbooks:

user name=mdehaan comment=awesome passwd=awWxVV.JvmdHw createhome=yes
user name=mdehaan groups=wheel,skynet
user name=mdehaan state=absent force=yes

virt¶

Manages virtual machines supported by libvirt. Requires that libvirt be installed on the managed machine.

guest:

The name of the guest VM being managed

state

Desired state of the VM. Either running, shutdown, destroyed, or undefined. Note that there may be some lag for state requests like ‘shutdown’, and these states only refer to the virtual machine states. After starting a guest, the guest OS may not be immediately accessible.

command:

In addition to state management, various non-idempotent commands are available for API and script usage (but don’t make much sense in a playbook). These mostly return information, though some also affect state. See examples below.

Example action from Ansible Playbooks:

virt guest=alpha state=running
virt guest=alpha state=shutdown
virt guest=alpha state=destroyed
virt guest=alpha state=undefined

Example guest management commands from /usr/bin/ansible:

ansible host -m virt -a "guest=foo command=status"
ansible host -m virt -a "guest=foo command=pause"
ansible host -m virt -a "guest=foo command=unpause"
ansible host -m virt -a "guest=foo command=get_xml"
ansible host -m virt -a "guest=foo command=autostart"

Example host (hypervisor) management commands from /usr/bin/ansible:

ansible host -m virt -a "command=freemem"
ansible host -m virt -a "command=list_vms"
ansible host -m virt -a "command=info"
ansible host -m virt -a "command=nodeinfo"
ansible host -m virt -a "command=virttype"

yum¶

Will install, upgrade, remove, and list packages with the yum package manager.

pkg:

A package name or package specifier with version, like name-1.0

state:

Can be either ‘installed’, ‘latest’, or ‘removed’. The default is ‘installed’.

list:

When ‘list’ is supplied instead of ‘state’, the yum module can list various configuration attributes. Values include ‘installed’, ‘updates’, ‘available’, ‘repos’, or any package specifier.

Example action from Ansible Playbooks:

yum pkg=httpd state=latest
yum pkg=httpd state=removed
yum pkg=httpd state=installed

Writing your own modules¶

See Module Development Guide.