Use variable only if defined in Ansible

ansible

My colleague and I use Ansible to manage a group of servers.

We use the .ansible.cfg file in our local home directories to setup our local environments and keep our playbooks in a git repo.

When authenticating to servers, I use user1, and he uses user2. 95% of of our servers have these accounts, but historically reasons, a few servers only have a "user" account.

We're using host_vars to set the remote_user variable for the minority of servers in question.

However, in our playbooks, we generally user "all" to stipulate what servers we want to hit, and use the –limit parameter on the command line to specify exactly which servers should get the update. Our server farm is a legacy of mis-mash poorly engineered servers that have to be kept online until they are retired in a few years, and we've found that this approach best suits our needs.

Our issue is that our remote_user parameter is set in our .ansible.cfg file, where it is exposed as environment variable rather than a script variable.

That means if our task contains:

remote_user: "{{ remote_user }}"

It will only work for hosts for which that variable is defined

For the 95% of hosts for which we don't define this variable, the task fails.

Is there a way to only use the variable if it is defined?

eg

If remote_user is defined, use it, if not, use the environment variable set in .ansible.cfg

Note: I know I can use:

- name: Do something 
  remote_user: "{{ remote_user }}"
  when: remote_user is defined

In a task definition, but that will only apply to that task, and I don't want to have to update all task

When I really need is for that condition to be available at the hosts definition, ie:

---
- hosts: all
    remote_user: "{{ remote_user }}"
    when: remote_user is defined

But that is illegal in Ansible

Best Answer

As usual, after spending 2 hours postponing asking the question here, I find the answer 5 mins after I post the question!

Its really simple. To set a different remote_user for individual systems without having to apply loads of hacks to existing playbooks, just add the var to the host in your inventory:

[web_servers]
server1 ansible_ssh_user=user
server2

In this instance, any time a play incldues server1, "user" will be used as the ssh user. For server2, the value of remote_user from your ansible.cfg file will be used (eg user1, user2 etc depending on the local environment).

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