Ansible Features I Missed

Well, ok some of these aren't particularly new, but I've only just become aware of them. Even after years of Ansible experience, there's always something to learn!

Module Defaults

It's been around since at least 2.7 and the docs are here.

If you frequently call the same module with the same arguments, it can be useful to define default arguments for that particular module using the module_defaults attribute.

If I've got a simple playbook, where I'm calling the same thing over and passing the same information a lot, this is really useful to cut down on duplication and error possibilities.

Where will I be using this mostly though? For spinning up all things public cloud.

The Module defaults group lets you define a whole load of commonly called variables, for AWS, Azure, VMware, k8s and others.

The docs example of setting the AWS region, is a good one. Each AWS module is going to mandate a region as an option, so set it only once so it can be used throughout those modules:

# example_play.yml

- hosts: localhost

  module_defaults:
    group/aws:
      region: us-west-2

  tasks:

  - name: Get info
    aws_s3_bucket_info:


  # now the region is shared between both info modules


  - name: Get info
    ec2_ami_info:
      filters:
        name: 'RHEL*7.5*'

That is useful and will cut down on YAML lines!

Anchors & Aliases

Jury's out for me on this one to be to honest!

But I think the java options example in the docs is a useful one.

...
vars:
    app1:
        jvm: &jvm_opts
            opts: '-Xms1G -Xmx2G'
            port: 1000
            path: /usr/lib/app1
    app2:
        jvm:
            <<: *jvm_opts

            
            path: /usr/lib/app2

This looks complicated on the face of it, but it's easy enough to understand -

&jvm_opts is the anchor, or "remember these values"

We can then re-use them for another app definition, using the *jvm_opts alias.

The outcome is that app1 and app2 share the same opts and port definitions, and the path value is merged using <<

For the more complex set of variable structures, this little trick could be useful!