Ansible: Set variable only if undefined

Question

I would like to set an ansible variable to some default value but only if the variable is undefined. Otherwise I would like to keep it unchanged.

I tried these two approaches and both of them produce recursive loop:

namespace: "{{namespace|default(default_namespace)}}" namespace: "{% if namespace is defined %}{{namespace}}{% else %}{{default_namespace}}{% endif %}" 

Answer 1

It seems like you are taking a wrong approach.

Take a look at the Ansible documentation concerning variable precedence. It is a built-in feature of Ansible to use the default variable if the variable is not defined.

In Ansible 2.x the variable precedence starts like this:

role defaults

inventory vars

So if you want to define a default value for a variable you should set it in role/defaults/main.yml. Ansible will use that value only if the variable is not defined somewhere else.

Another option is to use a Jinja2 filter. With a Jinja filter you can set a default value for a variable like this:

{{ some_variable | default(5) }} 

Answer 2

- set_fact: namespace="default_namespace"   when: namespace is undefined