rds_param_group: WARN on updating DBParameterGroupFamily (engine)

changelogs/fragments/1169-rds_param_group-fail-on-updating-engine.yml

@@ -0,0 +1,2 @@
+bugfixes:
+- rds_param_group - added a check to fail the task while modifying/updating rds_param_group if trying to change DB parameter group family. (https://github.com/ansible-collections/amazon.aws/pull/1169).

plugins/modules/rds_param_group.py

@@ -35,6 +35,8 @@
       - The type of database for this group.
       - Please use following command to get list of all supported db engines and their respective versions.
       - '# aws rds describe-db-engine-versions --query "DBEngineVersions[].DBParameterGroupFamily"'
+      - The DB parameter group family is immutable and can't be changed when updating a DB parameter group.
+        See U(https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-rds-dbparametergroup.html)
       - Required for I(state=present).
     type: str
   immediate:
@@ -266,6 +268,11 @@ def ensure_present(module, connection):
                 module.fail_json_aws(e, msg="Couldn't create parameter group")
     else:
         group = response['DBParameterGroups'][0]
+        db_parameter_group_family = group['DBParameterGroupFamily']
+
+        if module.params.get('engine') != db_parameter_group_family:
+            module.warn("The DB parameter group family (engine) can't be changed when updating a DB parameter group.")
+
         if tags:
             changed = update_tags(module, connection, group, tags)
 

tests/integration/targets/rds_param_group/defaults/main.yml

@@ -2,6 +2,7 @@ rds_param_group:
   name: '{{ resource_prefix}}rds-param-group'
   description: Test group for rds_param_group Ansible module
   engine: postgres9.6
+  engine_to_modify_to: postgres10
 
 rds_long_param_list:
   application_name: Test

tests/integration/targets/rds_param_group/tasks/main.yml

@@ -123,6 +123,27 @@
       - result.tags["Test"] == '123'
 
     # ============================================================
+
+  - name: test modifying rds parameter group engine/family (warning displayed)
+    rds_param_group:
+      name: '{{ rds_param_group.name }}'
+      engine: '{{ rds_param_group.engine_to_modify_to }}'
+      description: '{{ rds_param_group.description }}'
+      state: present
+      tags:
+        Environment: test
+        Test: 123
+    register: result
+
+  - name: verify that modifying rds param group engine/family displays warning
+    assert:
+      that:
+      - not result.changed
+      - not result.failed
+      - result.warnings is defined
+      - result.warnings | length > 0
+
+    # ============================================================
   - name: test tagging existing group - CHECK_MODE
     rds_param_group:
       name: '{{ rds_param_group.name }}'