hostname mapping support

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 = 34
+LIBPATCH = 35
 
 PYDEPS = ["ops>=2.0.0"]
 
@@ -2277,7 +2277,7 @@ def __init__(
 
 
 ################################################################################
-# Cross-charm Relatoins Data Handling and Evenets
+# Cross-charm Relations Data Handling and Events
 ################################################################################
 
 # Generic events
@@ -2300,7 +2300,7 @@ class RelationEventWithSecret(RelationEvent):
 
     @property
     def _secrets(self) -> dict:
-        """Caching secrets to avoid fetching them each time a field is referrd.
+        """Caching secrets to avoid fetching them each time a field is referred.
 
         DON'T USE the encapsulated helper variable outside of this function
         """
@@ -2309,7 +2309,7 @@ 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):
@@ -2498,6 +2498,17 @@ def version(self) -> Optional[str]:
 
         return self.relation.data[self.relation.app].get("version")
 
+    @property
+    def hostname_mapping(self) -> Optional[str]:
+        """Returns the hostname mapping.
+
+        A list that maps the hostnames to IP address.
+        """
+        if not self.relation.app:
+            return None
+
+        return self.relation.data[self.relation.app].get("hostname-mapping")
+
 
 class DatabaseCreatedEvent(AuthenticationEvent, DatabaseRequiresEvent):
     """Event emitted when a new database is created for use on this relation."""
@@ -2602,6 +2613,15 @@ def set_version(self, relation_id: int, version: str) -> None:
         """
         self.update_relation_data(relation_id, {"version": version})
 
+    def set_hostname_mapping(self, relation_id: int, hostname_mapping: list[dict]) -> None:
+        """Set hostname mapping.
+
+        Args:
+            relation_id: the identifier for a particular relation.
+            hostname_mapping: list of hostname mapping.
+        """
+        self.update_relation_data(relation_id, {"hostname-mapping": json.dumps(hostname_mapping)})
+
 
 class DatabaseProviderEventHandlers(EventHandlers):
     """Provider-side of the database relation handlers."""
@@ -3016,7 +3036,7 @@ class KafkaRequiresEvents(CharmEvents):
 # Kafka Provides and Requires
 
 
-class KafkaProvidesData(ProviderData):
+class KafkaProviderData(ProviderData):
     """Provider-side of the Kafka relation."""
 
     def __init__(self, model: Model, relation_name: str) -> None:
@@ -3059,12 +3079,12 @@ def set_zookeeper_uris(self, relation_id: int, zookeeper_uris: str) -> None:
         self.update_relation_data(relation_id, {"zookeeper-uris": zookeeper_uris})
 
 
-class KafkaProvidesEventHandlers(EventHandlers):
+class KafkaProviderEventHandlers(EventHandlers):
     """Provider-side of the Kafka relation."""
 
     on = KafkaProvidesEvents()  # pyright: ignore [reportAssignmentType]
 
-    def __init__(self, charm: CharmBase, relation_data: KafkaProvidesData) -> None:
+    def __init__(self, charm: CharmBase, relation_data: KafkaProviderData) -> None:
         super().__init__(charm, relation_data)
         # Just to keep lint quiet, can't resolve inheritance. The same happened in super().__init__() above
         self.relation_data = relation_data
@@ -3086,15 +3106,15 @@ def _on_relation_changed_event(self, event: RelationChangedEvent) -> None:
             )
 
 
-class KafkaProvides(KafkaProvidesData, KafkaProvidesEventHandlers):
+class KafkaProvides(KafkaProviderData, KafkaProviderEventHandlers):
     """Provider-side of the Kafka relation."""
 
     def __init__(self, charm: CharmBase, relation_name: str) -> None:
-        KafkaProvidesData.__init__(self, charm.model, relation_name)
-        KafkaProvidesEventHandlers.__init__(self, charm, self)
+        KafkaProviderData.__init__(self, charm.model, relation_name)
+        KafkaProviderEventHandlers.__init__(self, charm, self)
 
 
-class KafkaRequiresData(RequirerData):
+class KafkaRequirerData(RequirerData):
     """Requirer-side of the Kafka relation."""
 
     def __init__(
@@ -3124,12 +3144,12 @@ def topic(self, value):
         self._topic = value
 
 
-class KafkaRequiresEventHandlers(RequirerEventHandlers):
+class KafkaRequirerEventHandlers(RequirerEventHandlers):
     """Requires-side of the Kafka relation."""
 
     on = KafkaRequiresEvents()  # pyright: ignore [reportAssignmentType]
 
-    def __init__(self, charm: CharmBase, relation_data: KafkaRequiresData) -> None:
+    def __init__(self, charm: CharmBase, relation_data: KafkaRequirerData) -> None:
         super().__init__(charm, relation_data)
         # Just to keep lint quiet, can't resolve inheritance. The same happened in super().__init__() above
         self.relation_data = relation_data
@@ -3188,7 +3208,7 @@ def _on_relation_changed_event(self, event: RelationChangedEvent) -> None:
             return
 
 
-class KafkaRequires(KafkaRequiresData, KafkaRequiresEventHandlers):
+class KafkaRequires(KafkaRequirerData, KafkaRequirerEventHandlers):
     """Provider-side of the Kafka relation."""
 
     def __init__(
@@ -3200,7 +3220,7 @@ def __init__(
         consumer_group_prefix: Optional[str] = None,
         additional_secret_fields: Optional[List[str]] = [],
     ) -> None:
-        KafkaRequiresData.__init__(
+        KafkaRequirerData.__init__(
             self,
             charm.model,
             relation_name,
@@ -3209,7 +3229,7 @@ def __init__(
             consumer_group_prefix,
             additional_secret_fields,
         )
-        KafkaRequiresEventHandlers.__init__(self, charm, self)
+        KafkaRequirerEventHandlers.__init__(self, charm, self)
 
 
 # Opensearch related events

pyproject.toml

@@ -16,6 +16,7 @@ tenacity = "^8.2.3"
 poetry-core = "^1.7.0"
 jinja2 = "^3.1.2"
 requests = "^2.31.0"
+python-hosts = "*"
 
 [tool.poetry.group.charm-libs.dependencies]
 # data_platform_libs/v0/data_interfaces.py

src/abstract_charm.py

@@ -109,6 +109,11 @@ def _exposed_read_write_endpoint(self) -> str:
     def _exposed_read_only_endpoint(self) -> str:
         """The exposed read-only endpoint"""
 
+    @property
+    @abc.abstractmethod
+    def _hostname_mapping(self):
+        """Machine hostname mapping"""
+
     @abc.abstractmethod
     def is_externally_accessible(self, *, event) -> typing.Optional[bool]:
         """Whether endpoints should be externally accessible.
@@ -327,6 +332,9 @@ def reconcile(self, event=None) -> None:  # noqa: C901
                 ):
                     self._reconcile_ports(event=event)
 
+                    if connection_info := self._database_requires.get_connection_info(event=event):
+                        self._hostname_mapping.update_etc_hosts(connection_info)
+
             # Empty waiting status means we're waiting for database requires relation before
             # starting workload
             if not workload_.status or workload_.status == ops.WaitingStatus():

src/machine_charm.py

@@ -14,6 +14,7 @@
 import tenacity
 
 import abstract_charm
+import machine_hostname_mapping
 import machine_logrotate
 import machine_upgrade
 import machine_workload
@@ -85,6 +86,10 @@ def _exposed_read_write_endpoint(self) -> str:
     def _exposed_read_only_endpoint(self) -> str:
         return f"{self.host_address}:{self._READ_ONLY_PORT}"
 
+    @property
+    def _hostname_mapping(self) -> machine_hostname_mapping.MachineHostnameMapping:
+        return machine_hostname_mapping.MachineHostnameMapping()
+
     def is_externally_accessible(self, *, event) -> typing.Optional[bool]:
         return self._database_provides.external_connectivity(event)
 

src/machine_hostname_mapping.py

@@ -0,0 +1,41 @@
+# Copyright 2024 Canonical Ltd.
+# See LICENSE file for licensing details.
+
+"""hostname mapping configuration"""
+
+import logging
+
+from python_hosts import Hosts, HostsEntry
+
+from relations.database_requires import CompleteConnectionInformation
+
+logger = logging.getLogger(__name__)
+
+COMMENT = "Managed by mysql-router charm"
+
+
+class MachineHostnameMapping:
+    """Machine hostname mapping configuration"""
+
+    def __init__(self) -> None:
+        self._hosts = Hosts()
+
+    def update_etc_hosts(self, connection_info: CompleteConnectionInformation) -> None:
+        """Add a host to the hosts file.
+
+        Args:
+            connection_info: The relation CompleteConnectionInformation
+        """
+        if connection_info.hostname_mapping is None:
+            logger.debug("No hostname mapping to update")
+            return
+
+        logger.debug("Updating /etc/hosts")
+        host_entries = [
+            HostsEntry(entry_type="ipv4", comment=COMMENT, **entry)
+            for entry in connection_info.hostname_mapping
+        ]
+
+        self._hosts.remove_all_matching(comment=COMMENT)
+        self._hosts.add(host_entries, force=True, allow_address_duplication=True, merge_names=True)
+        self._hosts.write()

src/relations/database_requires.py

@@ -3,6 +3,7 @@
 
 """Relation to MySQL charm"""
 
+import json
 import logging
 import typing
 
@@ -87,6 +88,7 @@ def __init__(self, *, interface: data_interfaces.DatabaseRequires, event) -> Non
         self.port = endpoint.split(":")[1]
         self.username = databag["username"]
         self.password = databag["password"]
+        self.hostname_mapping = json.loads(databag["hostname-mapping"])
 
     @property
     def redacted(self):