Add external LB management handler hook interface

Based on conversation on an ansible issue[1], I implemented
a LB orchestration role[2] similar to the POC here[3].

This will allow external loadbalancer management roles to hook
into a universal notify listener "Manage LB" to perform before/
after endpoint management actions when the service is being
restarted.

[1]: https://github.com/ansible/ansible/issues/27813
[2]: https://github.com/Logan2211/ansible-haproxy-endpoints
[3]: https://github.com/Logan2211/tmp-ansible-27813

Change-Id: I7d2f47e94826526e9a5a99d32575f691fb6b30fd

doc/source/index.rst

@@ -33,10 +33,22 @@ Example playbook
 .. literalinclude:: ../../examples/playbook.yml
    :language: yaml
 
+External Restart Hooks
+~~~~~~~~~~~~~~~~~~~~~~
+
+When the role performs a restart of the service, it will notify an Ansible
+handler named ``Manage LB``, which is a noop within this role. In the
+playbook, other roles may be loaded before and after this role which will
+implement Ansible handler listeners for ``Manage LB``, allowing external roles
+to manage the load balancer endpoints responsible for sending traffic to the
+servers being restarted by marking them in maintenance or active mode,
+draining sessions, etc. For an example implementation, please reference the
+`ansible-haproxy-endpoints role <https://github.com/Logan2211/ansible-haproxy-endpoints>`_
+used by the openstack-ansible project.
+
 Tags
 ~~~~
 
 This role supports two tags: ``glance-install`` and ``glance-config``.
 The ``glance-install`` tag can be used to install and upgrade. The
 ``glance-config`` tag can be used to manage configuration.
-

handlers/main.yml

@@ -56,3 +56,7 @@
   retries: 5
   delay: 2
   listen: "Restart glance services"
+
+- meta: noop
+  listen: Manage LB
+  when: false

tasks/glance_init_systemd.yml

@@ -49,6 +49,7 @@
     group: "root"
   with_items: "{{ filtered_glance_services }}"
   notify:
+    - Manage LB
     - Restart glance services
 
 - name: Place the systemd init script
@@ -62,4 +63,5 @@
     config_type: "ini"
   with_items: "{{ filtered_glance_services }}"
   notify:
+    - Manage LB
     - Restart glance services

tasks/glance_install.yml

@@ -81,6 +81,7 @@
     copy: "no"
   when: glance_get_venv | changed
   notify:
+    - Manage LB
     - Restart glance services
 
 - name: Install pip packages
@@ -99,6 +100,7 @@
   delay: 2
   when: glance_get_venv | failed or glance_get_venv | skipped
   notify:
+    - Manage LB
     - Restart glance services
 
 - name: Remove python from path first (CentOS, openSUSE)

tasks/glance_post_install.yml

@@ -72,6 +72,7 @@
       config_overrides: "{{ glance_glance_rootwrap_conf_overrides }}"
       config_type: "ini"
   notify:
+    - Manage LB
     - Restart glance services
 
 - name: Create nfs shares local path

tasks/glance_uwsgi.yml

@@ -29,4 +29,5 @@
   with_items: "{{ filtered_glance_services }}"
   when: item.wsgi_app | default(False)
   notify:
+    - Manage LB
     - Restart glance services