Command Line¶

Parallelism and Shell Commands¶

Let’s use ansible’s command line tool to reboot all web servers in Atlanta, 10 at a time. First, let’s set up SSH-agent so it can remember our credentials:

$ ssh-agent bash
$ ssh-add ~/.ssh/id_rsa.pub

If you don’t want to use ssh-agent and want to instead SSH with a password instead of keys, you can with --ask-pass (-k), but it’s much better to just use ssh-agent.

Now to run the command on all servers in a group, in this case, atlanta, in 10 parallel forks:

$ ansible atlanta -a "/sbin/reboot" -f 10

In 0.7 and later, this will default to running from your user account. If you do not like this behavior, pass in “-u username”. (In 0.6 and before, it defaulted to root. Most folks prefered defaulting to the current user, so we changed it).

If you want to run commands as a different user, it looks like this:

$ ansible atlanta -a "/usr/bin/foo" -u username

If you want to run commands through sudo:

$ ansible atlanta -a "/usr/bin/foo" -u username --sudo [--ask-sudo-pass]

Use --ask-sudo-pass (-K) if you are not using passwordless sudo. This will interactively prompt you for the password to use. Use of passwordless sudo makes things easier to automate, but it’s not required.

It is also possible to sudo to a user other than root using --sudo-user (-U):

$ ansible atlanta -a "/usr/bin/foo" -u username -U otheruser [--ask-sudo-pass]

Ok, so those are basics. If you didn’t read about patterns and groups yet, go back and read Inventory & Patterns.

The -f 10 in the above specifies the usage of 10 simultaneous processes. Normally commands also take a -m for module name, but the default module name is command, so we didn’t need to specify that all of the time. We’ll use -m in later examples to run some other Ansible Modules.

Using the shell module looks like this:

$ ansible raleigh -m shell -a 'echo $TERM'

When running any command with the ansible ad hoc CLI (as opposed to Playbooks), pay particular attention to shell quoting rules, so the shell doesn’t eat a variable before it gets passed to Ansible. For example, using double vs single quotes in the above example would evaluate the variable on the box you were on.

So far we’ve been demoing simple command execution, but most Ansible modules usually do not work like simple scripts. They make the remote system look like you state, and run the commands necessary to get it there. This is commonly referred to as ‘idempotence’, and is a core design goal of ansible. However, we also recognize that running ad hoc commands is equally important, so Ansible easily supports both.

File Transfer & Templating¶

Here’s another use case for the /usr/bin/ansible command line.

Ansible can SCP lots of files to multiple machines in parallel, and optionally use them as template sources.

To transfer a file directly to many different servers:

$ ansible atlanta -m copy -a "src=/etc/hosts dest=/tmp/hosts"

If you use playbooks, you can also take advantage of the template module, which takes this another step further.

The file module allows changing ownership and permissions on files. These same options can be passed directly to the copy or template modules as well:

$ ansible webservers -m file -a "dest=/srv/foo/a.txt mode=600"
$ ansible webservers -m file -a "dest=/srv/foo/b.txt mode=600 owner=mdehaan group=mdehaan"

The file module can also create directories, similar to mkdir -p:

$ ansible webservers -m file -a "dest=/path/to/c mode=644 owner=mdehaan group=mdehaan state=directory"

As well as delete directories (recursively) and delete files:

$ ansible webservers -m file -a "dest=/path/to/c state=absent"

The mode, owner, and group arguments can also be used on the copy or template lines.

Managing Packages¶

There are modules available for yum and apt. Here are some examples with yum.

Ensure a package is installed, but don’t update it:

$ ansible webservers -m yum -a "pkg=acme state=installed"

Ensure a package is installed to a specific version:

$ ansible webservers -m yum -a "pkg=acme-1.5 state=installed"

Ensure a package is at the latest version:

$ ansible webservers -m yum -a "pkg=acme state=latest"

Ensure a package is not installed:

$ ansible webservers -m yum -a "pkg=acme state=removed"

Currently Ansible only has modules for managing packages with yum and apt. You can install for other packages for now using the command module or (better!) contribute a module for other package managers. Stop by the mailing list for info/details.

Users and Groups¶

The user module allows easy creation and manipulation of existing user accounts, as well as removal of user accounts that may exist:

$ ansible all -m user -a "name=foo password=<crypted password here>"

$ ansible all -m user -a "name=foo state=absent"

See the Ansible Modules section for details on all of the available options, including how to manipulate groups and group membership.

Deploying From Source Control¶

Deploy your webapp straight from git:

$ ansible webservers -m git -a "repo=git://foo.example.org/repo.git dest=/srv/myapp version=HEAD"

Since ansible modules can notify change handlers it is possible to tell ansible to run specific tasks when the code is updated, such as deploying Perl/Python/PHP/Ruby directly from git and then restarting apache.

Managing Services¶

Ensure a service is started on all webservers:

$ ansible webservers -m service -a "name=httpd state=started"

Alternatively, restart a service on all webservers:

$ ansible webservers -m service -a "name=httpd state=restarted"

Ensure a service is stopped:

$ ansible webservers -m service -a "name=httpd state=stopped"

Time Limited Background Operations¶

Long running operations can be backgrounded, and their status can be checked on later. The same job ID is given to the same task on all hosts, so you won’t lose track. If you kick hosts and don’t want to poll, it looks like this:

$ ansible all -B 3600 -a "/usr/bin/long_running_operation --do-stuff"

If you do decide you want to check on the job status later, you can:

$ ansible all -m async_status -a "jid=123456789"

Polling is built-in and looks like this:

$ ansible all -B 1800 -P 60 -a "/usr/bin/long_running_operation --do-stuff"

The above example says “run for 30 minutes max (-B: 30*60=1800), poll for status (-P) every 60 seconds”.

Poll mode is smart so all jobs will be started before polling will begin on any machine. Be sure to use a high enough --forks value if you want to get all of your jobs started very quickly. After the time limit (in seconds) runs out (-B), the process on the remote nodes will be terminated.

Any module other than copy or template can be backgrounded. Typically you’ll be backgrounding long-running shell commands or software upgrades only. Playbooks also support polling, and have a simplified syntax for this.

Limiting Selected Hosts¶

New in version 0.7.

What hosts you select to manage can be additionally constrained by using the ‘–limit’ parameter or by using ‘batch’ (or ‘range’) selectors.

As mentioned above, patterns can be strung together to select hosts in more than one group:

$ ansible webservers:dbservers -m command -a "/bin/foo xyz"

This is an “or” condition. If you want to further constrain the selection, use –limit, which also works with ansible-playbook:

$ ansible webservers:dbservers -m command -a "/bin/foo xyz" region

Now let’s talk about range selection. Suppose you have 1000 servers in group ‘datacenter’, but only want to target one at a time. This is also easy:

$ ansible webservers[0-99] -m command -a "/bin/foo xyz"
$ ansible webservers[100-199] -m command -a "/bin/foo xyz"

This will select the first 100, then the second 100, host entries in the webservers group. (It does not matter what their names or IP addresses are).

Both of these methods can be used at the same time, and ranges can also be passed to the –limit parameter.