How do I select a variable using a fact in my ansible playbook?

Question

I want to select different options based on the aws region and availability zone of my instances. As a very simple example, I'd like to set the timezone of the instance to the correct timezone based on the region.

I can get the region and the availability zone from the ohai_ec2 facts.

How do I use the fact to select from a list of variables?

I tried referencing the variable directly, and that works for when statements e.g.

when: ohai_ec2.region == "us-east-1"

I tried a lookup as in Create Variable From Ansible Facts , but have not gotten the format correct.

This works

# find the region
          - name: Base - find the region
            debug:
              msg: "Region is {{ ohai_ec2.region }} and zone is {{ ohai_ec2.availability_zone }}"

#Task: Base - Sets the timezone
          - name: Base - Set timezone to US East
            when: ohai_ec2.region == "us-east-1"
            timezone:
              name: US/Eastern
          - name: Base - Set timezone to CEST
            when: ohai_ec2.region == "eu-central-1"
            timezone:
              name: Europe/Madrid
          - name: Base - Set timezone to US West
            when: ohai_ec2.region == "us-west-2"
            timezone:
              name: US/Pacific

but this doesn't

...
        vars:
          mytz:
            us-east-1: "US/Eastern"
            us-west-2: "US/Pacific"
            eu-central-1: "Europe/Madrid"
...

          - name: Base - Set timezone to US East
            timezone:
              name: "{{ lookup ('vars', 'mytz'.'[ohai_ec2.region]') }}"

nor

          - name: Base - Set timezone to US East
            timezone:
              name: "{{ mytz.'[ohai_ec2.region]' }}"

I get this result

fatal: [xxxxxxxxxx-xxxx]: FAILED! => {"msg": "template error while templating string: expected name or number. String: {{ mytz.[ohai_ec2.region] }}"}

What is the correct way of using the fact and variable?

larsks larsks · Accepted Answer · 2019-08-13T21:47:27

If you have a dictionary named mytz (which you do), and you have a dictionary ohai_ec2 with a region key, you can use the value of that key to select a value from mytz like this:

{{ mytz[ohai_ec2.region] }}

Here's a runnable example:

---
- hosts: localhost
  gather_facts: false
  vars:
    mytz:
      us-east-1: "US/Eastern"
      us-west-2: "US/Pacific"
      eu-central-1: "Europe/Madrid"
    ohai_ec2:
      region: us-east-1

  tasks:
    - name: Base - Set timezone to US East
      timezone:
        name: "{{ mytz[ohai_ec2.region] }}"

How do I select a variable using a fact in my ansible playbook?

1 Answers