Enable feature flags post-upgrade

Stable feature flags must be enabled before upgrades to ensure
the service can still start. These additional tasks check for
any disabled feature flags and enable them. This is done
immediately after upgrades so that systems can run with them
enabled striaght away.

Closes-Bug: #2038818
Change-Id: I5211a30899f544a9f7e609e85551a92b245d25bf

releasenotes/notes/feature-flags-9faf32a3d49af4fc.yaml

@@ -0,0 +1,6 @@
+---
+upgrade:
+  - |
+    Support is added to enable all stable RabbitMQ feature flags by default.
+    This happens automatically post upgrade, and avoids compatibility issues
+    which could occur when installing a new version of RabbitMQ.

tasks/main.yml

@@ -81,3 +81,7 @@
 
 - name: Flush handlers
   meta: flush_handlers
+
+- name: Importing rabbitmq_feature_flags tasks
+  import_tasks: rabbitmq_feature_flags.yml
+  when: _rabbitmq_is_last_play_host

tasks/rabbitmq_feature_flags.yml

@@ -0,0 +1,45 @@
+---
+# Copyright 2024, BBC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+- name: "Gather cluster status"
+  command: "rabbitmqctl cluster_status --formatter json"
+  register: _cluster_status
+  changed_when: False
+  tags:
+    - rabbitmq-upgrade
+
+- name: "Only enable feature flags if all cluster members are up and stable"
+  block:
+    - name: "Check for disabled RabbitMQ feature flags"
+      shell: "rabbitmqctl list_feature_flags | grep disabled"
+      args:
+        executable: /bin/bash
+      register: _feature_flags
+      changed_when: False
+      failed_when: False
+
+    # NOTE: changed_when required despite the above check because 'unstable'
+    # feature flags will remain disabled each time this runs
+    - name: "Enable all RabbitMQ feature flags"
+      command: "rabbitmqctl enable_feature_flag all"
+      changed_when: False
+      when:
+        - (_feature_flags.stdout_lines | length) > 0
+  when:
+    - ((_cluster_status.stdout | from_json)['running_nodes'] | length) == (groups[rabbitmq_host_group] | length)
+    - ((_cluster_status.stdout | from_json)['alarms'] | length) == 0
+    - ((_cluster_status.stdout | from_json)['partitions'] | length) == 0
+  tags:
+    - rabbitmq-upgrade

vars/main.yml

@@ -0,0 +1,19 @@
+---
+# Copyright 2024, BBC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+_rabbitmq_is_last_play_host: >-
+  {{
+    (inventory_hostname == (groups[rabbitmq_host_group] | intersect(ansible_play_hosts)) | last) | bool
+  }}