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Mikhail T.
Asked: 2017-08-30 06:52:35 +0800 CST

How to trigger a custom error from inside a Jinja template?

  • 772

Though Ansible itself has a way for triggering a custom error, I can not find anything similar for Jinja.

My current method uses a syntax error:

{%  if 'ansible_mounts' in hostvars[host] %}
# {{ host }} knows its mount-points
{% else %}
# {% error!! No ansible_mounts listed for host - fact-gathering must've failed %}
{% endif %}

but those are rendered poorly at run-time -- one needs to look inside the template-file and search for the error (the rendering does not even include the line-number!).

Is there a way to output a neat failure message from inside Jinja-template?

ansible

4 Answers

  1. Best Answer

    Answer from the comment:

    There is no easy way to accomplish this – only via custom plugin. For details see: https://stackoverflow.com/questions/21778252/how-to-raise-an-exception-in-a-jinja2-macro

    • 3

  2. Ansible adds the mandatory filter to Jinja, which can be used to do this:

    {{ ('OK text' if condition_ok) | mandatory('Text of error message') }}

    gives the failure:

    fatal: [hostname]: FAILED! => {"msg": "Text of error message"}

    (Replace condition_ok with the check that you need to make; 'OK text' can be just '' if nothing should be substituted.)

    • 3

  3. I have written a jinja2 extension-jinja2_error to raise error.

    Firstly,

    pip install jinja2_error

    If you use it with ansible

    ANSIBLE_JINJA2_EXTENSIONS=jinja2_error.ErrorExtension ansible-playbook site.yml -v

    If you use it with jinja2 Environment

        from jinja2 import Environment

    from jinja2_error import jinja2_error

    if __name__ == '__main__':
        env = Environment(extensions=[jinja2_error.ErrorExtension])
        render_text = """
                {% if 1==1 %}
                  {% error "It's error" %}
                {% endif %}
                """
        template = env.from_string(render_text)
        result = template.render({"a": "b"})

    If you want to know the details, please access

    https://github.com/mumubin/jiaja2_error

    • 1

  4. For those who looking for like mandatory filter but not using ansible

    {%- if not param.columns %} 
{# use 'include' wrong way, so it raise a error #}
{% include "required 'params.columns' not found!" %}
{%- endif %}
    • 0