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: I5aecc26606f41bc6b27fbe9a5f600914a88ff2c7

doc/source/index.rst

@@ -31,6 +31,19 @@ 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
 ~~~~
 

handlers/main.yml

@@ -74,3 +74,7 @@
     - "'nova_compute' in group_names"
     - "nova_discover_hosts_in_cells_interval | int < 1"
   listen: "Restart nova services"
+
+- meta: noop
+  listen: Manage LB
+  when: false

tasks/consoles/nova_console_novnc_ssl.yml

@@ -39,6 +39,8 @@
   with_items:
     - { content: "{{ nova_console_user_ssl_combined.stdout ~ '\n' }}", dest: "{{ nova_console_ssl_cert }}", mode: "0644" }
     - { src: "{{ nova_console_user_ssl_key }}", dest: "{{ nova_console_ssl_key }}", mode: "0640" }
-  notify: Restart nova services
+  notify:
+    - Manage LB
+    - Restart nova services
   tags:
     - nova-config

tasks/nova_init_systemd.yml

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

tasks/nova_install.yml

@@ -118,7 +118,9 @@
     copy: "no"
   when:
     - nova_get_venv | changed
-  notify: Restart nova services
+  notify:
+    - Manage LB
+    - Restart nova services
   tags:
     - nova-pip-packages
 
@@ -138,7 +140,9 @@
   delay: 2
   when:
     - nova_get_venv | failed or nova_get_venv | skipped
-  notify: Restart nova services
+  notify:
+    - Manage LB
+    - Restart nova services
   tags:
     - nova-pip-packages
 

tasks/nova_post_install.yml

@@ -51,7 +51,9 @@
       dest: "/etc/nova/policy.json-{{ nova_venv_tag }}"
       config_overrides: "{{ nova_policy_overrides }}"
       config_type: "json"
-  notify: Restart nova services
+  notify:
+    - Manage LB
+    - Restart nova services
   tags:
     - nova-config
     - nova-post-install
@@ -64,7 +66,9 @@
     group: "root"
   with_fileglob:
     - rootwrap.d/*
-  notify: Restart nova services
+  notify:
+    - Manage LB
+    - Restart nova services
   tags:
     - nova-config
     - nova-post-install

tasks/nova_uwsgi.yml

@@ -30,6 +30,7 @@
   with_items: "{{ filtered_nova_services }}"
   when: item.wsgi_app | default(False)
   notify:
+    - Manage LB
     - Restart nova services
 
 # Cleanup and restart nginx configuration