In Ansible, how do I assign a hostvar to a playbook's host?

Question

The directory of my Ansible project has the following structure:

project/ playbook.yml host_vars/ localhsot.yml roles/ ... terraform-provision/ ... terraform/ ...

Here's project/playbook.yml:

- hosts: localhost tasks: - name: trigger role include_role: name: terraform-provision - hosts: hostvars['localhost'].aws_instance_host_group tasks: - name: debugging debug: var: hostvars['localhost'].aws_instance_host_group

Here's the relevant part of project/host_vars/localhost.yml:

hostvars['localhost'].aws_instance_host_group aws_instance_host_group: "aws_instance"

Here's the relevant part of project/roles/terraform-provision/tasks/main.yml:

- name: Add the provisioned AWS instance to the inventory add_host: name: "{{ aws_instance_public_ip.value }}" # set using set_fact elsewhere in file ansible_user: "{{ aws_instance_user_name }}" groups: "{{ aws_instance_host_group }}"

When I execute project/playbook.yml, it throws the following error when trying to connect to the host created by the terraform-provision role:

[WARNING]: Could not match supplied host pattern, ignoring: hostvars['localhost'].aws_instance_host_group

However, the debugging task of project/playbook.yml prints the group's name (aws_instance) successfully.

What am I missing? Is there a better approach to achieve the same thing?

Vladimir Botka · Accepted Answer · 2022-05-08 13:59:04Z

To be evaluated, a variable must be closed in quoted double curly braces, e.g.

- hosts: "{{ hostvars.localhost.aws_instance_host_group }}"

The dot notation simplifies the code.

^{Minimal reproducible example
shell> cat pb.yml --- - hosts: localhost gather_facts: false tasks: - set_fact: aws_instance_host_group: aws_instance - add_host: name: 10.1.0.61 groups: "{{ aws_instance_host_group }}" - hosts: "{{ hostvars.localhost.aws_instance_host_group }}" gather_facts: false tasks: - debug: var: groups - debug: var: inventory_hostname
shell> cat hosts localhost
shell> ansible-playbook -i hosts pb.yml PLAY [localhost] ***************************************************************************** TASK [set_fact] ****************************************************************************** ok: [localhost] TASK [add_host] ****************************************************************************** changed: [localhost] PLAY [aws_instance] ************************************************************************** TASK [debug] ********************************************************************************* ok: [10.1.0.61] => groups: all: - 10.1.0.61 - localhost aws_instance: - 10.1.0.61 ungrouped: - localhost TASK [debug] ********************************************************************************* ok: [10.1.0.61] => inventory_hostname: 10.1.0.61 PLAY RECAP *********************************************************************************** 10.1.0.61: ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0 localhost: ok=2 changed=1 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0}

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