Ansible - Use string in a variable lookup - ansible

Question

I'm trying to make my playbooks aware of their environment; that being production or stage.
My playbook first pulls the ec2_tag for its environment successfully and set to the variable 'env'. On the ec2 provision task, I would like to use the 'env' variable in the vpc and subnet lookups, so it grabs the correct one based on its environment. Below I tried adding the 'env' variable into the lookups, but I'm getting a full string back instead of it pulling it from my variable file.
Do I need to add some logic checks within the {{}}?
- name: Provision instance
ec2:
key_name: "{{ aws_public_key }}"
instance_type: t2.medium
image: "{{ aws_ubuntu_ami }}"
wait: true
vpc_subnet_id: "{{ env + '_subnet_public1' }}"
group_id: "{{ env + '_app_group' }}"
assign_public_ip: yes
instance_tags:
Name: "{{ sys_name }}"
Environment: "{{ env }}"
region: "{{ aws_region }}"
volumes:
- device_name: /dev/sda1
volume_size: 300
delete_on_termination: true
register: ec2

Answer 1

If you want to do variable interpolation then you'll need to use the hostvars[inventory_hostname]['variable'] syntax.
The FAQs cover this briefly but for your use case you should be able to do something like:
- name: Provision instance
ec2:
key_name: "{{ aws_public_key }}"
instance_type: t2.medium
image: "{{ aws_ubuntu_ami }}"
wait: true
vpc_subnet_id: hostvars[inventory_hostname][env + '_subnet_public1']
group_id: hostvars[inventory_hostname][env + '_app_group']
assign_public_ip: yes
instance_tags:
Name: "{{ sys_name }}"
Environment: "{{ env }}"
region: "{{ aws_region }}"
volumes:
- device_name: /dev/sda1
volume_size: 300
delete_on_termination: true
register: ec2