convert dictionary keys in playbook - ansible

Question

I have an existing playbook variable dictionary defined like:
vars:
resource_tags: {
Name: "some name"
Service: "some service"
}
This is used in various calls to tasks in this form. But in another task, I need it in a different format, and rather than have it hard-coded, I was wondering if it could be built in a task.
I need it to look like:
{
"tag:Name": "some name"
"tag:Service": "some service"
}
I tried iterating using with_dict and setting a fact with combine:
- set_fact:
ec2_remote_facts_filter: "{{ ec2_remote_facts_filter | default({}) | combine( { 'tag:'item.name: item.val } ) }}"
with_dict: "{{ ec2_count_resource_tags }}"
And obviously that doesn't work.
Is this even possible?

Answer 1

If you don't mind a bit of hackery:
- debug: msg="{{ resource_tags | to_json(indent=0) | regex_replace('\n\"','\n\"tag:') }}"
This will convert your dict into JSON-formatted string with indent=0, meaning each key will start from new line; then insert tag: after first double quote on every line.
Because the result is valid JSON, Ansible template engine will convert it back into dict as the last step of variable substitution, giving you:
ok: [localhost] => {
"msg": {
"tag:Name": "some name",
"tag:Service": "some service"
}
}
I suppose there may be some corner cases if there are newlines inside your values, but in general it should be fine.

Answer 2

Maybe you need a custom lookup plugin in your case.
1) Edit file ansible.cfg and uncomment key 'lookup_plugins' with value './plugins/lookup'
2) Create a plugin file named 'ec2remote.py' in './plugins/lookup'
3) Use it in your playbook:
- debug:
msg: "{{ item }}"
with_ec2remote: "{{ ec2_count_resource_tags }}"
4) Implements your ec2remote.py (many examples here)
class LookupModule(LookupBase):
def run(self, terms, **kwargs):
result = {}
for k,v in terms.items():
result["tag:"+k] = v
return result
Usually, I prefer to develop plugins that are easily usable and testable and thus preserve an understandable playbook.