[MISC] Improve k8s canonical DNS lookup (backport)

kubernetes/src/charm.py

@@ -15,7 +15,6 @@
 
 import logging
 import random
-from socket import getfqdn
 from time import sleep
 
 import ops
@@ -100,7 +99,7 @@
 from relations.mysql_provider import MySQLProvider
 from rotate_mysql_logs import RotateMySQLLogs, RotateMySQLLogsCharmEvents
 from upgrade import MySQLK8sUpgrade, get_mysql_k8s_dependencies_model
-from utils import compare_dictionaries, dotappend, generate_random_password
+from utils import compare_dictionaries, dotappend, generate_random_password, get_k8s_fqdn
 
 logger = logging.getLogger(__name__)
 
@@ -331,7 +330,7 @@ def get_unit_address(self, unit: Unit, relation_name: str = PEER) -> str:
         Translate juju unit name to resolvable hostname.
         """
         unit_hostname = self.get_unit_hostname(unit.name)
-        unit_dns_domain = getfqdn(self.get_unit_hostname(unit.name))
+        unit_dns_domain = get_k8s_fqdn(self.get_unit_hostname(unit.name))
 
         # When fully propagated, DNS domain name should contain unit hostname.
         # For example:
@@ -1063,7 +1062,7 @@ def _on_database_storage_detaching(self, _) -> None:
             logger.info("Switching primary to unit 0")
             try:
                 self._mysql.set_cluster_primary(
-                    new_primary_address=getfqdn(self.get_unit_hostname(f"{self.app.name}/0"))
+                    new_primary_address=get_k8s_fqdn(self.get_unit_hostname(f"{self.app.name}/0"))
                 )
             except MySQLSetClusterPrimaryError:
                 logger.warning("Failed to switch primary to unit 0")

kubernetes/src/relations/mysql_provider.py

@@ -4,7 +4,6 @@
 """Library containing the implementation of the standard relation."""
 
 import logging
-import socket
 import typing
 
 from charms.data_platform_libs.v0.data_interfaces import DatabaseProvides, DatabaseRequestedEvent
@@ -23,7 +22,7 @@
 
 from constants import CONTAINER_NAME, CONTAINER_RESTARTS, DB_RELATION_NAME, DEFAULT_PASSWORD_LENGTH
 from k8s_helpers import KubernetesClientError
-from utils import dotappend, generate_random_password
+from utils import dotappend, generate_random_password, get_k8s_fqdn
 
 logger = logging.getLogger(__name__)
 
@@ -145,8 +144,8 @@ def _on_database_requested(self, event: DatabaseRequestedEvent) -> None:
             # create k8s services for endpoints
             self.charm.k8s_helpers.create_endpoint_services(["primary", "replicas"])
 
-            primary_endpoint = dotappend(socket.getfqdn(f"{self.charm.app.name}-primary"))
-            replicas_endpoint = dotappend(socket.getfqdn(f"{self.charm.app.name}-replicas"))
+            primary_endpoint = dotappend(get_k8s_fqdn(f"{self.charm.app.name}-primary"))
+            replicas_endpoint = dotappend(get_k8s_fqdn(f"{self.charm.app.name}-replicas"))
 
             # wait for endpoints to be ready
             self.charm.k8s_helpers.wait_service_ready((primary_endpoint, 3306))

kubernetes/src/upgrade.py

@@ -5,7 +5,6 @@
 
 import json
 import logging
-from socket import getfqdn
 from typing import TYPE_CHECKING, override
 
 from charms.data_platform_libs.v0.upgrade import (
@@ -33,6 +32,7 @@
 
 import k8s_helpers
 from constants import CONTAINER_NAME, MYSQLD_SERVICE
+from utils import get_k8s_fqdn
 
 if TYPE_CHECKING:
     from charm import MySQLOperatorCharm
@@ -156,7 +156,7 @@ def _pre_upgrade_prepare(self) -> None:
         """
         if self.charm._mysql.get_primary_label() != f"{self.charm.app.name}-0":
             # set the primary to the first unit for switchover mitigation
-            new_primary = getfqdn(self.charm.get_unit_hostname(f"{self.charm.app.name}/0"))
+            new_primary = get_k8s_fqdn(self.charm.get_unit_hostname(f"{self.charm.app.name}/0"))
             self.charm._mysql.set_cluster_primary(new_primary)
 
         # set slow shutdown on all instances

kubernetes/src/utils.py

@@ -5,6 +5,7 @@
 
 import re
 import secrets
+import socket
 import string
 
 
@@ -91,3 +92,23 @@ def dotappend(string: str) -> str:
     if not string.endswith("."):
         string += "."
     return string
+
+
+def get_k8s_fqdn(name: str) -> str:
+    """Resolve the canonical FQDN for a Kubernetes service or pod name."""
+    try:
+        info = socket.getaddrinfo(
+            name,
+            None,
+            family=socket.AF_UNSPEC,
+            flags=socket.AI_CANONNAME,
+            type=socket.SOCK_STREAM,
+        )
+    except socket.gaierror as e:
+        raise RuntimeError(f"Failed to resolve canonical name for {name}") from e
+
+    for entry in info:
+        if canonname := entry[3]:
+            return canonname
+
+    raise RuntimeError(f"Could not determine canonical name for {name}")

kubernetes/tests/unit/test_charm.py

@@ -315,6 +315,17 @@ def test_on_config_changed(self):
             self.charm.peers.data[self.charm.app]["cluster-name"], "not_valid_cluster_name"
         )
 
+    @patch(
+        "charm.get_k8s_fqdn",
+        return_value="mysql-k8s-0.mysql-k8s-endpoints.default.svc.cluster.local",
+    )
+    def test_get_unit_address(self, mock_get_k8s_fqdn):
+        self.assertEqual(
+            self.charm.get_unit_address(self.charm.unit),
+            "mysql-k8s-0.mysql-k8s-endpoints.default.svc.cluster.local.",
+        )
+        mock_get_k8s_fqdn.assert_called_once_with("mysql-k8s-0.mysql-k8s-endpoints")
+
     @patch("charm.MySQLOperatorCharm.get_unit_address", return_value="mysql-k8s.somedomain")
     @patch("mysql_k8s_helpers.MySQL.is_data_dir_initialised", return_value=False)
     def test_mysql_property(self, _, mock_get_unit_address):

kubernetes/tests/unit/test_database.py

@@ -67,8 +67,10 @@ def tearDown(self) -> None:
     @patch(
         "relations.mysql_provider.generate_random_password", return_value="super_secure_password"
     )
+    @patch("relations.mysql_provider.get_k8s_fqdn")
     def test_database_requested(
         self,
+        mock_get_k8s_fqdn,
         _generate_random_password,
         _create_scoped_user,
         _create_database,
@@ -80,6 +82,8 @@ def test_database_requested(
         _cluster_metadata_exists,
         _get_unit_address,
     ):
+        mock_get_k8s_fqdn.side_effect = ["mysql-k8s-primary", "mysql-k8s-replicas"]
+
         # run start-up events to enable usage of the helper class
         self.harness.set_leader(True)
         self.harness.container_pebble_ready("mysql")
@@ -124,3 +128,4 @@ def test_database_requested(
         _create_endpoint_services.assert_called_once()
         _update_endpoints.assert_called()
         _wait_service_ready.assert_called_once()
+        self.assertEqual(mock_get_k8s_fqdn.call_count, 2)

kubernetes/tests/unit/test_upgrade.py

@@ -133,10 +133,14 @@ def test_log_rollback(self, mock_logging):
     @patch("mysql_k8s_helpers.MySQL.set_dynamic_variable")
     @patch("mysql_k8s_helpers.MySQL.get_primary_label", return_value="mysql-k8s-1")
     @patch("mysql_k8s_helpers.MySQL.set_cluster_primary")
+    @patch(
+        "upgrade.get_k8s_fqdn", return_value="mysql-k8s-0.mysql-k8s-endpoints.svc.cluster.local"
+    )
     @patch("k8s_helpers.KubernetesHelpers.set_rolling_update_partition")
     def test_pre_upgrade_prepare(
         self,
         mock_set_rolling_update_partition,
+        mock_get_k8s_fqdn,
         mock_set_cluster_primary,
         mock_get_primary_label,
         mock_set_dynamic_variable,
@@ -148,7 +152,10 @@ def test_pre_upgrade_prepare(
 
         self.charm.upgrade._pre_upgrade_prepare()
 
-        mock_set_cluster_primary.assert_called_once()
+        mock_set_cluster_primary.assert_called_once_with(
+            "mysql-k8s-0.mysql-k8s-endpoints.svc.cluster.local"
+        )
+        mock_get_k8s_fqdn.assert_called_once_with("mysql-k8s-0.mysql-k8s-endpoints")
         mock_get_primary_label.assert_called_once()
         mock_set_rolling_update_partition.assert_called_once()
         assert mock_set_dynamic_variable.call_count == 2

kubernetes/tests/unit/test_utils.py

@@ -1,9 +1,11 @@
 # Copyright 2023 Canonical Ltd.
 # See LICENSE file for licensing details.
 
+import socket
 import unittest
+from unittest.mock import patch
 
-from utils import any_memory_to_bytes, generate_random_password, split_mem
+from utils import any_memory_to_bytes, generate_random_password, get_k8s_fqdn, split_mem
 
 
 class TestUtils(unittest.TestCase):
@@ -21,3 +23,81 @@ def test_any_memory_to_bytes(self):
         self.assertEqual(any_memory_to_bytes("1Gi"), 1073741824)
         self.assertEqual(any_memory_to_bytes("1G"), 10**9)
         self.assertEqual(any_memory_to_bytes("1024"), 1024)
+
+    @patch("utils.socket.getaddrinfo")
+    def test_get_k8s_fqdn(self, mock_getaddrinfo):
+        mock_getaddrinfo.return_value = [
+            (
+                None,
+                None,
+                None,
+                "",
+                None,
+            ),
+            (
+                None,
+                None,
+                None,
+                "mysql-2.mysql-endpoints.default.svc.cluster.local.",
+                None,
+            ),
+        ]
+
+        self.assertEqual(
+            get_k8s_fqdn("mysql-2.mysql-endpoints"),
+            "mysql-2.mysql-endpoints.default.svc.cluster.local.",
+        )
+        mock_getaddrinfo.assert_called_once_with(
+            "mysql-2.mysql-endpoints",
+            None,
+            family=socket.AF_UNSPEC,
+            flags=socket.AI_CANONNAME,
+            type=socket.SOCK_STREAM,
+        )
+
+    @patch("utils.socket.getaddrinfo", side_effect=socket.gaierror)
+    def test_get_k8s_fqdn_resolution_error(self, mock_getaddrinfo):
+        with self.assertRaisesRegex(
+            RuntimeError, "Failed to resolve canonical name for mysql-2.mysql-endpoints"
+        ):
+            get_k8s_fqdn("mysql-2.mysql-endpoints")
+
+        mock_getaddrinfo.assert_called_once_with(
+            "mysql-2.mysql-endpoints",
+            None,
+            family=socket.AF_UNSPEC,
+            flags=socket.AI_CANONNAME,
+            type=socket.SOCK_STREAM,
+        )
+
+    @patch("utils.socket.getaddrinfo")
+    def test_get_k8s_fqdn_without_canonical_name(self, mock_getaddrinfo):
+        mock_getaddrinfo.return_value = [
+            (
+                None,
+                None,
+                None,
+                "",
+                None,
+            ),
+            (
+                None,
+                None,
+                None,
+                "",
+                None,
+            ),
+        ]
+
+        with self.assertRaisesRegex(
+            RuntimeError, "Could not determine canonical name for mysql-2.mysql-endpoints"
+        ):
+            get_k8s_fqdn("mysql-2.mysql-endpoints")
+
+        mock_getaddrinfo.assert_called_once_with(
+            "mysql-2.mysql-endpoints",
+            None,
+            family=socket.AF_UNSPEC,
+            flags=socket.AI_CANONNAME,
+            type=socket.SOCK_STREAM,
+        )