Syntax errors with Jinja2 control structures in tasks file

[Alexander Z]

Hi Ansible community,

I am observing syntax error on attempt to use Jinja2 control structures in the tasks file:

Code

/opt/ansible/roles/network/tasks/network.yml:

{% if publicavailable|default(False) == False and public|default("") == "" and datacenter != "XXX" and datacenter != "YYY" %}
{% set private_interface = ansible_default_ipv4.interface %}
{% else %}
{% set private_interface = ansible_default_ipv4.interface|regex_replace('\d+','')|string + (ansible_default_ipv4.interface|regex_replace('\D+','')|int+1)|string %}
{% endif %}
- name: alias interface on private servers
  template:
    src: if_internal_eth.j2
    dest: /etc/network/interfaces.d/if_{{ private_interface }}_0.cfg
    owner: root
    group: root
    mode: 0644
  when: 'datacenter != "XXX" and datacenter != "YYY" and vlan_prefix2|default("") != ""'

Error

fatal: [host.domain.tld]: FAILED! => {"reason": "Syntax Error while loading YAML.
  found character that cannot start any token
The error appears to have been in /opt/ansible/roles/network/tasks/network.yml: line 52, column 2, but may
be elsewhere in the file depending on the exact syntax problem.
The offending line appears to be:

{% if publicavailable|default(False) == False and public|default(\"\") == \"\" and datacenter != \"XXX\" and datacenter != \"YYY\" %}
 ^ here
"}

Versions

ansible 2.5.10

python version = 2.7.12

Ubuntu 16.04.3 LTS

Kindly advise!

Thank you,

Alex

[Brian Coca]

That is because that is not a feature of Ansible.

Ansible parses the files using a YAML loader, then it does use jinja2
internally for templating, but only on SOME of the values in the data
structure returned by YAML.

----------
Brian Coca

[Alexander Z]

Hi Brian,

Thank you for the prompt reply.

Is there is any documentation describing that limitation? 

For example it renders correctly some variables inside {{ ... }} but does not allows to use control structures {% ... %} to define those variables.

Kindly advise!

Thank you,

Alex