Evaluate variable lazily - ansible

Question

I have a variable reference to a variable that is not known when the Playbook starts and the reference is evaluated. Is there a way to lazy load the variable when it is actually accessed?
In the inventory:
all:
hosts:
l01lin08:
bamboo_agents_it:
- bamboo_agent_app_name: bamboo-agent-it
bamboo_agent_install_dir: /data/bamboo-agent-it
bamboo_agent_capabilities: "{{ bamboo_agent_capabilities_it }}"
- # ...
- # ...
bamboo_agent_capabilities_it:
# Error: bamboo_agent_install_dir is not known when evaluating the variable
capabilitiy: '{{ bamboo_agent_install_dir }}/bla/blubb'
another.one: 123
is.something: true
bamboo_agent_capabilities_it.capability references to bamboo_agents_it[].bamboo_agent_install_dir which is not known in this context.
The capabilities is a set of key-value-pairs which can be everything. The values are not always paths and the keys are not always the same. Thus I cannot tell when to add a parent path and when not in the target task.
In the playbook I call a role in a loop over bamboo_agents_it:
tasks:
Install all bamboo agents
- include_role:
name: bamboo-agent-linux
vars:
bamboo_agent_app_name: '{{ item.bamboo_agent_app_name }}'
bamboo_agent_install_dir: '{{ item.bamboo_agent_install_dir }}'
bamboo_agent_capabilities: '{{ item.bamboo_agent_capabilities }}'
loop: '{{ bamboo_agents_it }}'
In this loop item.bamboo_agent_install_dir is available but I want to have a generic config definition. I don't want to handle these single keys separately.
Is there a way to solve this problem in a generic way?
Maybe can I lazyload the variable in the task when it is accessed?
A workaround I'm using is to replace a placeholder insteed. But I hope there is more idiomatic way:
# Inventory
bamboo_agent_capabilities_it:
# Error: bamboo_agent_install_dir is not known when evaluating the variable
capabilitiy: '[bamboo_agent_install_dir]/bla/blubb'
# Task:
lineinfile:
path: '{{ bamboo_agent_install_dir }}/bin/bamboo-capabilities.properties'
line: '{{ item.key }}={{ item.value | replace("[bamboo_agent_install_dir]", bamboo_agent_install_dir) }}'
loop: '{{ bamboo_agent_default_capabilities | dict2items + bamboo_agent_capabilities | dict2items }}'

Answer 1

What you could do is to declare the name that you would expect the variable to be named after:
bamboo_agent_capabilities_it:
capability: /foo/bar
dir: bamboo_agent_install_dir
Then use the vars lookup to fetch the value of that variable, for example:
bamboo_agent_capabilities: "{{ lookup('vars', item.bamboo_agent_capabilities.dir) }}{{ item.bamboo_agent_capabilities.capability }}"
Given the playbook:
- hosts: localhost
gather_facts: no
vars:
bamboo_agents_it:
- bamboo_agent_capabilities: "{{ bamboo_agent_capabilities_it }}"
bamboo_agent_capabilities_it:
capability: /foo/bar
dir: bamboo_agent_install_dir
tasks:
- set_fact:
bamboo_agent_install_dir: /path/to/dir
- debug:
msg:
bamboo_agent_capabilities: "{{ lookup('vars', item.bamboo_agent_capabilities.dir) }}{{ item.bamboo_agent_capabilities.capability }}"
loop: "{{ bamboo_agents_it }}"
This yields:
PLAY [localhost] ***************************************************************************************************
TASK [set_fact] ****************************************************************************************************
ok: [localhost]
TASK [debug] *******************************************************************************************************
ok: [localhost] => (item={'bamboo_agent_capabilities': {'capability': '/foo/bar', 'dir': 'bamboo_agent_install_dir'}}) =>
msg:
bamboo_agent_capabilities: /path/to/dir/foo/bar
PLAY RECAP *********************************************************************************************************
localhost : ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0