Fix Designate not to use etcd coordination backend

etcd via tooz does not support group membership required by
Designate coordination.
The best k-a can do is not to configure etcd in Designate.

Change-Id: I2f64f928e730355142ac369d8868cf9f65ca357e
Closes-bug: #1872205
Related-bug: #1840070

ansible/group_vars/all.yml

@@ -880,8 +880,8 @@ designate_backend: "bind9"
 designate_ns_record: "sample.openstack.org"
 designate_backend_external: "no"
 designate_backend_external_bind9_nameservers: ""
-# Valid options are [ '', redis, etcd ]
-designate_coordination_backend: "{{ 'redis' if enable_redis|bool else 'etcd' if enable_etcd|bool else '' }}"
+# Valid options are [ '', redis ]
+designate_coordination_backend: "{{ 'redis' if enable_redis|bool else '' }}"
 
 #######################
 # Neutron options

ansible/roles/designate/templates/designate.conf.j2

@@ -103,10 +103,8 @@ policy_file = {{ designate_policy_file }}
 [coordination]
 {% if designate_coordination_backend == 'redis' %}
 backend_url = {{ redis_connection_string }}
-{% elif designate_coordination_backend == 'etcd' %}
-# NOTE(yoctozepto): etcd-compatible tooz drivers do not support multiple endpoints here (verified in Stein, Train)
-# NOTE(yoctozepto): we must use etcd3gw (aka etcd3+http) due to issues with alternative (etcd3) and eventlet (as used by designate)
-# see https://bugs.launchpad.net/kolla-ansible/+bug/1854932
-# and https://review.opendev.org/466098 for details
-backend_url = etcd3+http://{{ 'api' | kolla_address(groups['etcd'][0]) | put_address_in_context('url') }}:{{ etcd_client_port }}
 {% endif %}
+{#
+  NOTE(yoctozepto): etcd is not supported due to lack of group membership
+                    support via tooz, see https://launchpad.net/bugs/1872205
+#}

doc/source/reference/networking/designate-guide.rst

@@ -39,10 +39,11 @@ Configure Designate options in ``/etc/kolla/globals.yml``
 
 .. important::
 
-   If multiple nodes are assigned to be Designate workers then you must
-   enable a supported coordination backend, currently either 'redis' or
-   'etcd'. The backend choice can be overridden by the
-   ``designate_coordination_backend`` variable.
+   If multiple nodes are assigned to be Designate workers, then you must
+   enable a supported coordination backend, currently only ``redis``
+   is supported. The backend choice can be overridden via the
+   ``designate_coordination_backend`` variable. It defaults to ``redis``
+   when ``redis`` is enabled (``enable_redis`` is set to ``yes``).
 
 The following additional variables are required depending on which backend you
 intend to use:

etc/kolla/globals.yml

@@ -499,8 +499,8 @@
 # Valid options are [ bind9 ]
 #designate_backend: "bind9"
 #designate_ns_record: "sample.openstack.org"
-# Valid options are [ '', redis, etcd ]
-#designate_coordination_backend: "{{ 'redis' if enable_redis|bool else 'etcd' if enable_etcd|bool else '' }}"
+# Valid options are [ '', redis ]
+#designate_coordination_backend: "{{ 'redis' if enable_redis|bool else '' }}"
 
 ########################
 # Nova - Compute Options

releasenotes/notes/bug-1872205-2eb7e57e0a334fb7.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fixes ``designate-worker`` not to use ``etcd`` as its coordination backend
+    because it is not supported by Designate (no group membership support
+    available via tooz).
+    `LP#1872205 <https://launchpad.net/bugs/1872205>`__