DPE-2352 Restart mysql exporter upon monitoring password change (#285)

* Restart mysql exporter upon monitoring password change

* Add restart_mysql_exporter as an abstract method on MySQLBase

lib/charms/mysql/v0/mysql.py

@@ -88,6 +88,7 @@ def wait_until_mysql_connection(self) -> None:
     BACKUPS_USERNAME,
     CLUSTER_ADMIN_PASSWORD_KEY,
     CLUSTER_ADMIN_USERNAME,
+    COS_AGENT_RELATION_NAME,
     MONITORING_PASSWORD_KEY,
     MONITORING_USERNAME,
     PASSWORD_LENGTH,
@@ -110,7 +111,7 @@ def wait_until_mysql_connection(self) -> None:
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 38
+LIBPATCH = 39
 
 UNIT_TEARDOWN_LOCKNAME = "unit-teardown"
 UNIT_ADD_LOCKNAME = "unit-add"
@@ -404,6 +405,12 @@ def _on_set_password(self, event: ActionEvent) -> None:
 
         self.set_secret("app", secret_key, new_password)
 
+        if (
+            username == MONITORING_USERNAME
+            and len(self.model.relations.get(COS_AGENT_RELATION_NAME, [])) > 0
+        ):
+            self._mysql.restart_mysql_exporter()
+
     def _get_cluster_status(self, event: ActionEvent) -> None:
         """Action used  to retrieve the cluster status."""
         if status := self._mysql.get_cluster_status():
@@ -2295,6 +2302,11 @@ def start_mysqld(self) -> None:
         """Starts the mysqld process."""
         raise NotImplementedError
 
+    @abstractmethod
+    def restart_mysql_exporter(self) -> None:
+        """Restart the mysqld exporter."""
+        raise NotImplementedError
+
     @abstractmethod
     def wait_until_mysql_connection(self) -> None:
         """Wait until a connection to MySQL has been obtained.

src/mysql_vm_helpers.py

@@ -566,6 +566,11 @@ def stop_mysql_exporter(self) -> None:
             logger.exception("An exception occurred when stopping mysqld-exporter")
             raise MySQLExporterConnectError("Error stopping mysqld-exporter")
 
+    def restart_mysql_exporter(self) -> None:
+        """Restart the mysqld exporter."""
+        self._stop_mysql_exporter()
+        self._connect_mysql_exporter()
+
     def _run_mysqlsh_script(self, script: str, timeout=None) -> str:
         """Execute a MySQL shell script.