example lookup plugin for ansible

app_defaults.py

import ansible.utils as utils
#
# Put this file in lookup_plugins/ alongside your playbooks.
#
# Lookup plugins can be called two ways: via with_ as a task loop
# construct, or via lookup('name').
# 
# You can find the code for the basic lookup plugins here:
# v1: https://github.com/ansible/ansible/tree/devel/v1/ansible/runner/lookup_plugins
# v2: https://github.com/ansible/ansible/tree/devel/lib/ansible/plugins/lookup
#

class LookupModule(object):
    def __init__(self, basedir=None, **kwargs):
        self.basedir = basedir

    def run(self, terms, inject=None, **kwargs):
        # "listify" basically dereferences a variable name passed into the plugin
        # ie: with_app_defaults:
        #      - foo
        #      - bar
        # 
        # ...where foo and bar are data structures.
        # 
        terms = utils.listify_lookup_plugin_terms(terms, self.basedir, inject)
        apps = utils.listify_lookup_plugin_terms(terms[0], self.basedir, inject)
        app_defaults = utils.listify_lookup_plugin_terms(terms[1], self.basedir, inject)

        # everything below is very specific to the application --you'll need to change
        # it to suit your needs. perhaps you could use it to merge the global security
        # groups data structure with the region-specific list and return a flattened list.
        results = []

        # .......
        # each item in the *_packages list -- can be either a string, to take the default
        # instance from app_defaults, or a dict, in which case we might specify a list of
        # instances (ports)
        for x in apps:
            # if hostvars specifies an instance list, use it. if not, take the first one
            # from the defaults.
            name = x['name']
            if 'instances' in x:
                instances = x['instances']
            else:
                instances = [app_defaults[name]['ports'][0]]

            if name not in app_defaults:
                print "WARNING: invalid application name:", x
                continue

            for instance in instances:
                y = dict(app_defaults[name])
                del y['ports']
                y['instance'] = instance
                y['app_name'] = name
                results.append(y)
        return results

test-lookup.yml

# this is just to test the custom lookup plugin
- hosts: all
  gather_facts: false
  connection: local

  vars_files:
  - vars/app_defaults.yml

  tasks:
  - name: shut down services (app)
    debug: msg="shutting down {{item.app_name}} on port {{item.instance}}"
    with_app_defaults:
    - apps_packages
    - app_defaults