How to build a conditional command in Ansible?

Question

Currently, my task looks like this:

- name: Create snapshot
  command: nodetool -u foo -pw bar snapshot

The -u (username) and -pw (password) are credentials to use nodetool. However, not all environments have authentication for nodetool. In case they don't have authentication, then I would need to use the task without -u and -pw, like:

- name: Create snapshot
  command: nodetool snapshot

I don't want to have two playbooks (one for authentication required environments, and one for without it). So I'm looking for something of the sort:

- name: Create snapshot
  command: nodetool [IF(auth_required){-u foo -pw bar}] snapshot

With auth_required being a boolean variable in my vars file. How can I do something like this in Ansible?

Answer 1

Use the module set_fact to create the variable my_cmd and use the filter ternary to branch the control flow. For example,

shell> cat pb.yml
- hosts: localhost

  tasks:

    - set_fact:
        my_cmd: "nodetool {{ params }}snapshot"
      vars:
        params: "{{ auth_required | bool |
                    ternary('-u foo -pw bar ', '') }}"

    - debug:
        var: my_cmd

gives

shell> ansible-playbook pb.yml -e auth_required=false
  ...
  my_cmd: nodetool snapshot

shell> ansible-playbook pb.yml -e auth_required=true
  ...
  my_cmd: nodetool -u foo -pw bar snapshot

Test it. Then, use the command

    - name: Create snapshot
      command: "{{ my_cmd }}"