variables in hostname doesn't work well with jinja2 templates

[Aneesh Joseph]

I'm using variables within the inventory host name to provision environments dynamically using the ansible openstack modules and this is working well

[openstack]
myserver-{{env}}.subdomain.mycompany.com

but, when I try to use these hostnames in a jinja2 template snippet, it's giving me errors

- name: find list of openstack servers which
  set_fact:
    openstack_servers: "{% for host in groups['openstack'] %}{{ hostvars[host]['inventory_hostname']{% if not loop.last %},{% endif %}{% endfor %}"

Is there a way to make it working? Any help or references in this regard  will be appreciated :-) 

To  replicate this kind of error, run the below play (test.yml) with the below inventory file(inventory.txt)

test.yml

---
- hosts: openstack
  connection: local
  tasks:
  - debug: msg="inventory_hostname={{inventory_hostname}}"
  - debug: msg="openstack_hosts={% for host in groups['openstack'] %}{{ hostvars[host]['inventory_hostname']}}{% if not loop.last %},{% endif %}{% endfor %}"

inventory.txt

[openstack]
myserver-{{env}}.subdomain.mycompany.com

and run the play using

ansible-playbook test.yml -i inventory.txt --extra-vars="env=dev1"

The play fails with the below error :(

PLAY [openstack] ***************************************************************

TASK [setup] *******************************************************************

ok: [myserver-{{env}}.subdomain.mycompany.com]

TASK [debug] *******************************************************************

ok: [myserver-{{env}}.subdomain.mycompany.com] => {

    "msg": "inventory_hostname=myserver-dev1.subdomain.mycompany.com"

}

TASK [debug] *******************************************************************

fatal: [myserver-{{env}}.subdomain.mycompany.com]: FAILED! => {"failed": true, "msg": "the field 'args' has an invalid value, which appears to include a variable that is undefined. The error was: 'ansible.vars.hostvars.HostVars object' has no attribute u'myserver-dev1.subdomain.mycompany.com'\n\nThe error appears to have been in '/home/hos/test.yml': line 6, column 5, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n  - debug: msg=\"inventory_hostname={{inventory_hostname}}\"\n  - debug: msg=\"openstack_hosts={% for host in groups['openstack'] %}{{ hostvars[host]['inventory_hostname']}}{% if not loop.last %},{% endif %}{% endfor %}\"\n    ^ here\nWe could be wrong, but this one looks like it might be an issue with\nmissing quotes.  Always quote template expression brackets when they\nstart a value. For instance:\n\n    with_items:\n      - {{ foo }}\n\nShould be written as:\n\n    with_items:\n      - \"{{ foo }}\"\n"}

NO MORE HOSTS LEFT *************************************************************

        to retry, use: --limit @test.retry

PLAY RECAP *********************************************************************

myserver-{{env}}.subdomain.mycompany.com : ok=2    changed=0    unreachable=0    failed=1

[Aneesh Joseph]

looks like ansible lazily loads the hostvars dict with the raw hostname and doesn't apply variable substitution, but the for other dicts like groups variable substitutions are applied. Is this a bug?

The hostvars dict has myserver-{{env}}.subdomain.mycompany.com as the key instead of myserver-dev1.subdomain.mycompany.com and ansible fails with the error The error was: 'ansible.vars.hostvars.HostVars object' has no attribute u'myserver-dev1.subdomain.mycompany.com

[Aneesh Joseph]

raised a GitHub issue for the same :) - https://github.com/ansible/ansible/issues/16565