feat: add support for DNS names with Connector (#1204)

The Connector may be configured to use a DNS name to look up the instance
name instead of configuring the connector with the instance connection name directly.

Add a DNS TXT record for the Cloud SQL instance to a private DNS server
or a private Google Cloud DNS Zone used by your application. For example:

Record type: TXT
Name: prod-db.mycompany.example.com – This is the domain name used by the application
Value: my-project:my-region:my-instance – This is the instance connection name

Configure the Connector to use a DNS name via setting resolver=DnsResolver

Author: jackwotherspoon

README.md

@@ -365,6 +365,69 @@ conn = connector.connect(
 )
 ```
 
+### Using DNS domain names to identify instances
+
+The connector can be configured to use DNS to look up an instance. This would
+allow you to configure your application to connect to a database instance, and
+centrally configure which instance in your DNS zone.
+
+#### Configure your DNS Records
+
+Add a DNS TXT record for the Cloud SQL instance to a **private** DNS server
+or a private Google Cloud DNS Zone used by your application.
+
+> [!NOTE]
+>
+> You are strongly discouraged from adding DNS records for your
+> Cloud SQL instances to a public DNS server. This would allow anyone on the
+> internet to discover the Cloud SQL instance name.
+
+For example: suppose you wanted to use the domain name
+`prod-db.mycompany.example.com` to connect to your database instance
+`my-project:region:my-instance`. You would create the following DNS record:
+
+* Record type: `TXT`
+* Name: `prod-db.mycompany.example.com` – This is the domain name used by the application
+* Value: `my-project:my-region:my-instance` – This is the Cloud SQL instance connection name
+
+#### Configure the connector
+
+Configure the connector to resolve DNS names by initializing it with
+`resolver=DnsResolver` and replacing the instance connection name with the DNS
+name in `connector.connect`:
+
+```python
+from google.cloud.sql.connector import Connector, DnsResolver
+import pymysql
+import sqlalchemy
+
+# helper function to return SQLAlchemy connection pool
+def init_connection_pool(connector: Connector) -> sqlalchemy.engine.Engine:
+    # function used to generate database connection
+    def getconn() -> pymysql.connections.Connection:
+        conn = connector.connect(
+            "prod-db.mycompany.example.com",  # using DNS name
+            "pymysql",
+            user="my-user",
+            password="my-password",
+            db="my-db-name"
+        )
+        return conn
+
+    # create connection pool
+    pool = sqlalchemy.create_engine(
+        "mysql+pymysql://",
+        creator=getconn,
+    )
+    return pool
+
+# initialize Cloud SQL Python Connector with `resolver=DnsResolver`
+with Connector(resolver=DnsResolver) as connector:
+    # initialize connection pool
+    pool = init_connection_pool(connector)
+    # ... use SQLAlchemy engine normally
+```
+
 ### Using the Python Connector with Python Web Frameworks
 
 The Python Connector can be used alongside popular Python web frameworks such

google/cloud/sql/connector/__init__.py

@@ -18,12 +18,16 @@
 from google.cloud.sql.connector.connector import create_async_connector
 from google.cloud.sql.connector.enums import IPTypes
 from google.cloud.sql.connector.enums import RefreshStrategy
+from google.cloud.sql.connector.resolver import DefaultResolver
+from google.cloud.sql.connector.resolver import DnsResolver
 from google.cloud.sql.connector.version import __version__
 
 __all__ = [
     "__version__",
     "create_async_connector",
     "Connector",
+    "DefaultResolver",
+    "DnsResolver",
     "IPTypes",
     "RefreshStrategy",
 ]

google/cloud/sql/connector/connector.py

@@ -37,6 +37,8 @@
 import google.cloud.sql.connector.pg8000 as pg8000
 import google.cloud.sql.connector.pymysql as pymysql
 import google.cloud.sql.connector.pytds as pytds
+from google.cloud.sql.connector.resolver import DefaultResolver
+from google.cloud.sql.connector.resolver import DnsResolver
 from google.cloud.sql.connector.utils import format_database_user
 from google.cloud.sql.connector.utils import generate_keys
 
@@ -63,6 +65,7 @@ def __init__(
         user_agent: Optional[str] = None,
         universe_domain: Optional[str] = None,
         refresh_strategy: str | RefreshStrategy = RefreshStrategy.BACKGROUND,
+        resolver: Type[DefaultResolver] | Type[DnsResolver] = DefaultResolver,
     ) -> None:
         """Initializes a Connector instance.
 
@@ -104,6 +107,13 @@ def __init__(
                 of the following: RefreshStrategy.LAZY ("LAZY") or
                 RefreshStrategy.BACKGROUND ("BACKGROUND").
                 Default: RefreshStrategy.BACKGROUND
+
+            resolver (DefaultResolver | DnsResolver): The class name of the
+                resolver to use for resolving the Cloud SQL instance connection
+                name. To resolve a DNS record to an instance connection name, use
+                DnsResolver.
+                Default: DefaultResolver
+
         """
         # if refresh_strategy is str, convert to RefreshStrategy enum
         if isinstance(refresh_strategy, str):
@@ -157,6 +167,7 @@ def __init__(
         self._enable_iam_auth = enable_iam_auth
         self._quota_project = quota_project
         self._user_agent = user_agent
+        self._resolver = resolver()
         # if ip_type is str, convert to IPTypes enum
         if isinstance(ip_type, str):
             ip_type = IPTypes._from_str(ip_type)
@@ -269,13 +280,14 @@ async def connect_async(
         if (instance_connection_string, enable_iam_auth) in self._cache:
             cache = self._cache[(instance_connection_string, enable_iam_auth)]
         else:
+            conn_name = await self._resolver.resolve(instance_connection_string)
             if self._refresh_strategy == RefreshStrategy.LAZY:
                 logger.debug(
                     f"['{instance_connection_string}']: Refresh strategy is set"
                     " to lazy refresh"
                 )
                 cache = LazyRefreshCache(
-                    instance_connection_string,
+                    conn_name,
                     self._client,
                     self._keys,
                     enable_iam_auth,
@@ -286,7 +298,7 @@ async def connect_async(
                     " to backgound refresh"
                 )
                 cache = RefreshAheadCache(
-                    instance_connection_string,
+                    conn_name,
                     self._client,
                     self._keys,
                     enable_iam_auth,

google/cloud/sql/connector/exceptions.py

@@ -70,3 +70,10 @@ class IncompatibleDriverError(Exception):
     Exception to be raised when the database driver given is for the wrong
     database engine. (i.e. asyncpg for a MySQL database)
     """
+
+
+class DnsResolutionError(Exception):
+    """
+    Exception to be raised when an instance connection name can not be resolved
+    from a DNS record.
+    """

google/cloud/sql/connector/instance.py

@@ -24,7 +24,7 @@
 
 from google.cloud.sql.connector.client import CloudSQLClient
 from google.cloud.sql.connector.connection_info import ConnectionInfo
-from google.cloud.sql.connector.connection_name import _parse_instance_connection_name
+from google.cloud.sql.connector.connection_name import ConnectionName
 from google.cloud.sql.connector.exceptions import RefreshNotValidError
 from google.cloud.sql.connector.rate_limiter import AsyncRateLimiter
 from google.cloud.sql.connector.refresh_utils import _is_valid
@@ -45,25 +45,23 @@ class RefreshAheadCache:
 
     def __init__(
         self,
-        instance_connection_string: str,
+        conn_name: ConnectionName,
         client: CloudSQLClient,
         keys: asyncio.Future,
         enable_iam_auth: bool = False,
     ) -> None:
         """Initializes a RefreshAheadCache instance.
 
         Args:
-            instance_connection_string (str): The Cloud SQL Instance's
-                connection string (also known as an instance connection name).
+            conn_name (ConnectionName): The Cloud SQL instance's
+                connection name.
             client (CloudSQLClient): The Cloud SQL Client instance.
             keys (asyncio.Future): A future to the client's public-private key
                 pair.
             enable_iam_auth (bool): Enables automatic IAM database authentication
                 (Postgres and MySQL) as the default authentication method for all
                 connections.
         """
-        # validate and parse instance connection name
-        conn_name = _parse_instance_connection_name(instance_connection_string)
         self._project, self._region, self._instance = (
             conn_name.project,
             conn_name.region,

google/cloud/sql/connector/lazy.py

@@ -21,7 +21,7 @@
 
 from google.cloud.sql.connector.client import CloudSQLClient
 from google.cloud.sql.connector.connection_info import ConnectionInfo
-from google.cloud.sql.connector.connection_name import _parse_instance_connection_name
+from google.cloud.sql.connector.connection_name import ConnectionName
 from google.cloud.sql.connector.refresh_utils import _refresh_buffer
 
 logger = logging.getLogger(name=__name__)
@@ -38,25 +38,23 @@ class LazyRefreshCache:
 
     def __init__(
         self,
-        instance_connection_string: str,
+        conn_name: ConnectionName,
         client: CloudSQLClient,
         keys: asyncio.Future,
         enable_iam_auth: bool = False,
     ) -> None:
         """Initializes a LazyRefreshCache instance.
 
         Args:
-            instance_connection_string (str): The Cloud SQL Instance's
-                connection string (also known as an instance connection name).
+            conn_name (ConnectionName): The Cloud SQL instance's
+                connection name.
             client (CloudSQLClient): The Cloud SQL Client instance.
             keys (asyncio.Future): A future to the client's public-private key
                 pair.
             enable_iam_auth (bool): Enables automatic IAM database authentication
                 (Postgres and MySQL) as the default authentication method for all
                 connections.
         """
-        # validate and parse instance connection name
-        conn_name = _parse_instance_connection_name(instance_connection_string)
         self._project, self._region, self._instance = (
             conn_name.project,
             conn_name.region,

google/cloud/sql/connector/resolver.py

@@ -0,0 +1,67 @@
+# Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import dns.asyncresolver
+
+from google.cloud.sql.connector.connection_name import _parse_instance_connection_name
+from google.cloud.sql.connector.connection_name import ConnectionName
+from google.cloud.sql.connector.exceptions import DnsResolutionError
+
+
+class DefaultResolver:
+    """DefaultResolver simply validates and parses instance connection name."""
+
+    async def resolve(self, connection_name: str) -> ConnectionName:
+        return _parse_instance_connection_name(connection_name)
+
+
+class DnsResolver(dns.asyncresolver.Resolver):
+    """
+    DnsResolver resolves domain names into instance connection names using
+    TXT records in DNS.
+    """
+
+    async def resolve(self, dns: str) -> ConnectionName:  # type: ignore
+        try:
+            conn_name = _parse_instance_connection_name(dns)
+        except ValueError:
+            # The connection name was not project:region:instance format.
+            # Attempt to query a TXT record to get connection name.
+            conn_name = await self.query_dns(dns)
+        return conn_name
+
+    async def query_dns(self, dns: str) -> ConnectionName:
+        try:
+            # Attempt to query the TXT records.
+            records = await super().resolve(dns, "TXT", raise_on_no_answer=True)
+            # Sort the TXT record values alphabetically, strip quotes as record
+            # values can be returned as raw strings
+            rdata = [record.to_text().strip('"') for record in records]
+            rdata.sort()
+            # Attempt to parse records, returning the first valid record.
+            for record in rdata:
+                try:
+                    conn_name = _parse_instance_connection_name(record)
+                    return conn_name
+                except Exception:
+                    continue
+            # If all records failed to parse, throw error
+            raise DnsResolutionError(
+                f"Unable to parse TXT record for `{dns}` -> `{rdata[0]}`"
+            )
+        # Don't override above DnsResolutionError
+        except DnsResolutionError:
+            raise
+        except Exception as e:
+            raise DnsResolutionError(f"Unable to resolve TXT record for `{dns}`") from e

requirements.txt

@@ -1,5 +1,6 @@
 aiofiles==24.1.0
 aiohttp==3.11.9
 cryptography==44.0.0
+dnspython==2.7.0
 Requests==2.32.3
 google-auth==2.36.0

setup.py

@@ -28,6 +28,7 @@
     "aiofiles",
     "aiohttp",
     "cryptography>=42.0.0",
+    "dnspython>=2.0.0",
     "Requests",
     "google-auth>=2.28.0",
 ]

tests/conftest.py

@@ -26,6 +26,7 @@
 from unit.mocks import FakeCSQLInstance  # type: ignore
 
 from google.cloud.sql.connector.client import CloudSQLClient
+from google.cloud.sql.connector.connection_name import ConnectionName
 from google.cloud.sql.connector.instance import RefreshAheadCache
 from google.cloud.sql.connector.utils import generate_keys
 
@@ -144,7 +145,7 @@ async def fake_client(
 async def cache(fake_client: CloudSQLClient) -> AsyncGenerator[RefreshAheadCache, None]:
     keys = asyncio.create_task(generate_keys())
     cache = RefreshAheadCache(
-        "test-project:test-region:test-instance",
+        ConnectionName("test-project", "test-region", "test-instance"),
         client=fake_client,
         keys=keys,
     )