[DPE-3927] Collect readonly dbs (#228)

* Collect read only databases

* Fixes

* Fail the action if not run against the leader

* Only collect if backend is up

* Backoff action

* Update libs

lib/charms/data_platform_libs/v0/data_interfaces.py

@@ -331,7 +331,7 @@ def _on_topic_requested(self, event: TopicRequestedEvent):
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 35
+LIBPATCH = 37
 
 PYDEPS = ["ops>=2.0.0"]
 
@@ -642,22 +642,26 @@ def _move_to_new_label_if_needed(self):
             return
 
         # Create a new secret with the new label
-        old_meta = self._secret_meta
         content = self._secret_meta.get_content()
+        self._secret_uri = None
 
         # I wish we could just check if we are the owners of the secret...
         try:
             self._secret_meta = self.add_secret(content, label=self.label)
         except ModelError as err:
             if "this unit is not the leader" not in str(err):
                 raise
-        old_meta.remove_all_revisions()
+        self.current_label = None
 
     def set_content(self, content: Dict[str, str]) -> None:
         """Setting cached secret content."""
         if not self.meta:
             return
 
+        # DPE-4182: do not create new revision if the content stay the same
+        if content == self.get_content():
+            return
+
         if content:
             self._move_to_new_label_if_needed()
             self.meta.set_content(content)
@@ -1586,7 +1590,7 @@ def _register_secret_to_relation(
         """
         label = self._generate_secret_label(relation_name, relation_id, group)
 
-        # Fetchin the Secret's meta information ensuring that it's locally getting registered with
+        # Fetching the Secret's meta information ensuring that it's locally getting registered with
         CachedSecret(self._model, self.component, label, secret_id).meta
 
     def _register_secrets_to_relation(self, relation: Relation, params_name_list: List[str]):
@@ -2309,7 +2313,7 @@ def _secrets(self) -> dict:
         return self._cached_secrets
 
     def _get_secret(self, group) -> Optional[Dict[str, str]]:
-        """Retrieveing secrets."""
+        """Retrieving secrets."""
         if not self.app:
             return
         if not self._secrets.get(group):

lib/charms/operator_libs_linux/v2/snap.py

@@ -83,7 +83,7 @@
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 5
+LIBPATCH = 7
 
 
 # Regex to locate 7-bit C1 ANSI sequences
@@ -319,7 +319,10 @@ def get(self, key: Optional[str], *, typed: bool = False) -> Any:
                 Default is to return a string.
         """
         if typed:
-            config = json.loads(self._snap("get", ["-d", key]))
+            args = ["-d"]
+            if key:
+                args.append(key)
+            config = json.loads(self._snap("get", args))
             if key:
                 return config.get(key)
             return config
@@ -584,13 +587,16 @@ def ensure(
                     "Installing snap %s, revision %s, tracking %s", self._name, revision, channel
                 )
                 self._install(channel, cohort, revision)
-            else:
+                logger.info("The snap installation completed successfully")
+            elif revision is None or revision != self._revision:
                 # The snap is installed, but we are changing it (e.g., switching channels).
                 logger.info(
                     "Refreshing snap %s, revision %s, tracking %s", self._name, revision, channel
                 )
                 self._refresh(channel=channel, cohort=cohort, revision=revision, devmode=devmode)
-            logger.info("The snap installation completed successfully")
+                logger.info("The snap refresh completed successfully")
+            else:
+                logger.info("Refresh of snap %s was unnecessary", self._name)
 
         self._update_snap_apps()
         self._state = state

src/charm.py

@@ -15,6 +15,7 @@
 from configparser import ConfigParser
 from typing import Dict, List, Literal, Optional, Union, get_args
 
+import psycopg2
 from charms.data_platform_libs.v0.data_interfaces import DataPeerData, DataPeerUnitData
 from charms.grafana_agent.v0.cos_agent import COSAgentProvider
 from charms.operator_libs_linux.v1 import systemd
@@ -402,6 +403,44 @@ def _on_start(self, _) -> None:
     def _on_leader_elected(self, _):
         self.peers.update_leader()
 
+    def _get_readonly_dbs(self, databases: Dict) -> Dict[str, str]:
+        readonly_dbs = {}
+        if self.backend.relation and "*" in databases:
+            read_only_endpoints = self.backend.get_read_only_endpoints()
+            r_hosts = ",".join([r_host.split(":")[0] for r_host in read_only_endpoints])
+            if r_hosts:
+                for r_host in read_only_endpoints:
+                    r_port = r_host.split(":")[1]
+                    break
+
+                backend_databases = json.loads(self.peers.app_databag.get("readonly_dbs", "[]"))
+                for name in backend_databases:
+                    readonly_dbs[f"{name}_readonly"] = {
+                        "host": r_hosts,
+                        "dbname": name,
+                        "port": r_port,
+                        "auth_dbname": databases["*"]["auth_dbname"],
+                        "auth_user": self.backend.auth_user,
+                    }
+        return readonly_dbs
+
+    def _collect_readonly_dbs(self) -> None:
+        if self.unit.is_leader() and self.backend.postgres:
+            existing_dbs = [db["name"] for db in self.get_relation_databases().values()]
+            existing_dbs += ["postgres", "pgbouncer"]
+            try:
+                with self.backend.postgres._connect_to_database(
+                    PGB
+                ) as conn, conn.cursor() as cursor:
+                    cursor.execute("SELECT datname FROM pg_database WHERE datistemplate = false;")
+                    results = cursor.fetchall()
+                conn.close()
+            except psycopg2.Error:
+                logger.warning("PostgreSQL connection failed")
+            readonly_dbs = [db[0] for db in results if db and db[0] not in existing_dbs]
+            readonly_dbs.sort()
+            self.peers.app_databag["readonly_dbs"] = json.dumps(readonly_dbs)
+
     def _on_update_status(self, _) -> None:
         """Update Status hook.
 
@@ -411,6 +450,7 @@ def _on_update_status(self, _) -> None:
         self.update_status()
 
         self.peers.update_leader()
+        self._collect_readonly_dbs()
 
     def update_status(self):
         """Health check to update pgbouncer status based on charm state."""
@@ -645,6 +685,7 @@ def render_pgb_config(self, reload_pgbouncer=False):
         with open("templates/pgb_config.j2", "r") as file:
             template = Template(file.read())
             databases = self._get_relation_config()
+            readonly_dbs = self._get_readonly_dbs(databases)
             enable_tls = all(self.tls.get_tls_files()) and self._is_exposed
             if self._is_exposed:
                 addr = "*"
@@ -657,6 +698,7 @@ def render_pgb_config(self, reload_pgbouncer=False):
                     f"{app_conf_dir}/{INSTANCE_DIR}{service_id}/pgbouncer.ini",
                     template.render(
                         databases=databases,
+                        readonly_databases=readonly_dbs,
                         peer_id=service_id,
                         base_socket_dir=f"{app_temp_dir}/{INSTANCE_DIR}",
                         peers=self.service_ids,

templates/pgb_config.j2

@@ -2,6 +2,9 @@
 {% for name, database in databases.items() -%}
 {{ name }} = host={{ database.host }} {% if database.dbname %}dbname={{ database.dbname }}{% else %}auth_dbname={{ database.auth_dbname }}{% endif %} port={{ database.port }} auth_user={{ database.auth_user }}
 {% endfor %}
+{% for name, database in readonly_databases.items() -%}
+{{ name }} = host={{ database.host }} dbname={{ database.dbname }} auth_dbname={{ database.auth_dbname }} port={{ database.port }} auth_user={{ database.auth_user }}
+{% endfor %}
 
 [peers]
 {% for peer in peers -%}

tests/unit/test_charm.py

@@ -374,6 +374,7 @@ def test_render_pgb_config(
         for i in range(self.charm._cores):
             expected_content = template.render(
                 databases=expected_databases,
+                readonly_databases={},
                 peer_id=i,
                 peers=range(self.charm._cores),
                 base_socket_dir="/tmp/pgbouncer/instance_",
@@ -420,6 +421,7 @@ def test_render_pgb_config(
         for i in range(self.charm._cores):
             expected_content = template.render(
                 databases=expected_databases,
+                readonly_databases={},
                 peer_id=i,
                 peers=range(self.charm._cores),
                 base_socket_dir="/tmp/pgbouncer/instance_",