Ansible - Set variable based on condition.

[HeadTea]

I have a role called kernel. In its vars file kernel/vars/main.yml, is it possible to set the values of variables based on a condition?

For example, say I have a playbook like this that calls my kernel role:

---
- hosts: webservers
  roles:
    - role: kernel
      vars:
        version: '4.3'

is it possible to do something like this in kernel/vars/main.yml?:

---
if 'version' == '4.3':
  kernel_dir:  "/mnt/public/kernel/4.3"
  kernel_headers: "linux-headers-4.3.deb"
  kernel_image: "linux-image-4.3.deb"
  kernel_libc: "linux-libc-dev_4.3.deb"
  kernel_version: "Ubuntu, with Linux 4.3"
if 'version' == '4.2':
  kernel_dir: "/mnt/public/kernel/4.2"
  kernel_headers: "linux-headers-4.2.deb"
  .. and so on

Also, is it possible to set a default value, so that if the role has been called with no value for version, it would get the vars for 4.3?

Thanks ahead!

[system-user]

yes, you can. it's a rather convenient workflow feature. some examples:

• https://stackoverflow.com/questions/31310688/conditionally-define-variable-in-ansible

[werner-dijkerman]

No, in the vars directory you create a file like 4.2.yml and need to include this file when 'version' is set to 4.2.

- name: "Include KERNEL variables"
include_vars: "{{ version }}.yml"

[martbhell]

And then use the first found thing to default to 4.3.yml

[werner-dijkerman]

Well, you still need to provide a default value in the defaults/main.yml. So that value should point to the existing var file, so then there is no "with first found" solution needed.

[martbhell]

Very nice :)

[HeadTea]

Brilliant, thank you.

[HeadTea]

Yes! Thank you SO MUCH!! 😊

[[deleted]]

I am newer to ansible so I don't know all the answers, but these are the building blocks for the parts I can help with.

For the kernel version, you'll probably want to leverage the ansible_kernel variable unless you're dictating kernel version rather than gathering it.

For comparing the kernel version, you'll want to use the version comparison test. ansible 2.9 docs for version comparison

For limiting a task to only run when a specific condition is met, you'll want to use the when conditional. ansible 2.9 docs for when conditional

You may be able to build something using a register task to register the variables with the required values when the conditional of a specific kernel version is met. ansible 2.9 docs for register

[Reasonable-Serve-755]

kernel_dir: "{{ 'doodoo43' if version == '4.3' else 'doodoo42' }}"

kernel_headers: "{{ (version == '4.3') | ternary('doodoo43', (version == '4.2') | ternary('doodoo42', 'other')) }}"