Set environment in Ansible doesn't seem to work - ansible

Question

The Consul lookup plugin has the following code. I would like to override by setting the environment variable for ANSIBLE_CONSUL_URL. I can't seem to get my task to use the environment variable. The task runs fine if I set the environment variable manually prior to running the task.
self.agent_url = 'http://localhost:8500'
if os.getenv('ANSIBLE_CONSUL_URL') is not None:
self.agent_url = os.environ['ANSIBLE_CONSUL_URL']
My task:
- name: Build list of modules and its associated tag
environment:
ANSIBLE_CONSUL_URL: "http://indeploy001.local.domain:8500"
set_fact: deploy_list="{{ item | replace("deploys/" + environment_id + "/",'') }}-{{ lookup('consul_kv','deploys/' + environment_id + '/' + item) }}"
with_items: "{{ modules }}"
register: deploy_list_result
Error
TASK: [Build list of modules and its associated tag] **************************
fatal: [127.0.0.1] => Failed to template deploy_list="{{ item | replace("deploys/" + environment_id + "/",'') }}-{{ lookup('consul_kv','deploys/' + environment_id + '/' + item) }}": Error locating 'deploys/sf/ariaserver' in kv store. Error was HTTPConnectionPool(host='localhost', port=8500): Max retries exceeded with url: /v1/kv/deploys/sf/ariaserver (Caused by NewConnectionError('<requests.packages.urllib3.connection.HTTPConnection object at 0x1eac410>: Failed to establish a new connection: [Errno 111] Connection refused',))
FATAL: all hosts have already failed -- aborting

Answer 1

Lookups are a templating feature. The keys of a task are rendered to resolve any Jinja expressions before the task is executed. That means your lookup is executed before the task is executed. The environment key simply is a task property, which has an effect when the task is executed. But you're not getting that far.
Also, I'm not 100% sure what would happen with your environment in this special case used in a set_fact task. set_fact is an action plugin, running on the control machine. So do lookups. But the task itself is not delegated to localhost. So it's possible the env var would be set for the control machine or on the remote machine. My guess though is, it is not set at all, neither on localhost nor remotely. The reason for my guess is, many action plugins do later in the process call a module with the same name, which then is executed on the target host. The logical behavior, and what a user would expect, would be that the env var then is set on the remote host by the module. Just a guess and neglectable given the first paragraph.
Conclusion:
If a lookup plugin is depending on environment variables, you can not set them in the same task. They need to be set previously - what you already found working.