docs: Add sample Cloud Run example application

samples/cloudrun/README.md

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+# Connecting Cloud Run to Cloud SQL with the Python Connector
+
+This guide provides a comprehensive walkthrough of how to connect a Cloud Run service to a Cloud SQL instance using the Cloud SQL Python Connector. It covers connecting to instances with both public and private IP addresses and demonstrates how to handle database credentials securely.
+
+## Develop a Python Application
+
+The following Python applications demonstrate how to connect to a Cloud SQL instance using the Cloud SQL Python Connector.
+
+### `mysql/main.py` and `postgres/main.py`
+
+These files contain the core application logic for connecting to a Cloud SQL for MySQL or PostgreSQL instance. They provide two separate authentication methods, each exposed at a different route:
+- `/`: Password-based authentication
+- `/iam`: IAM-based authentication
+
+
+### `sqlserver/main.py`
+
+This file contains the core application logic for connecting to a Cloud SQL for SQL Server instance. It uses the `cloud-sql-python-connector` to create a SQLAlchemy connection pool with password-based authentication at the `/` route.
+
+> [!NOTE]
+>
+> Cloud SQL for SQL Server does not support IAM database authentication.
+
+
+> [!NOTE]
+> **Lazy Refresh**
+>
+> The sample code in all three `main.py` files initializes the `Connector` with `refresh_strategy=lazy`. This is a recommended approach to avoid connection errors and optimize cost by preventing background processes from running when the CPU is throttled.
+
+## Global Variables and Lazy Instantiation
+
+In a Cloud Run service, global variables are initialized when the container instance starts up. The application instance then handles subsequent requests until the container is spun down.
+
+The `Connector` and SQLAlchemy `Engine` objects are defined as global variables (initially set to `None`) and are lazily instantiated (created only when needed) inside the request handlers.
+
+This approach offers several benefits:
+
+1.  **Faster Startup:** By deferring initialization until the first request, the Cloud Run service can start listening for requests almost immediately, reducing cold start latency.
+2.  **Resource Efficiency:** Expensive operations, like establishing background connections or fetching secrets, are only performed when actually required.
+3.  **Connection Reuse:** Once initialized, the global `Connector` and `Engine` instances are reused for all subsequent requests to that container instance. This prevents the overhead of creating new connections for every request and avoids hitting connection limits.
+
+## IAM Authentication Prerequisites
+
+
+For IAM authentication to work, you must ensure two things:
+
+1.  **The Cloud Run service's service account has the `Cloud SQL Client` role.** You can grant this role with the following command:
+    ```bash
+    gcloud projects add-iam-policy-binding PROJECT_ID \
+        --member="serviceAccount:SERVICE_ACCOUNT_EMAIL" \
+        --role="roles/cloudsql.client"
+    ```
+    Replace `PROJECT_ID` with your Google Cloud project ID and `SERVICE_ACCOUNT_EMAIL` with the email of the service account your Cloud Run service is using.
+
+2.  **The service account is added as a database user to your Cloud SQL instance.** You can do this with the following command:
+    ```bash
+    gcloud sql users create SERVICE_ACCOUNT_EMAIL \
+        --instance=INSTANCE_NAME \
+        --type=cloud_iam_user
+    ```
+    Replace `SERVICE_ACCOUNT_EMAIL` with the same service account email and `INSTANCE_NAME` with your Cloud SQL instance name.
+
+For Password-based authentication to work:
+
+1.  **The Cloud Run service's service account has the `Secret Accessor` role.** You can grant this role with the following command:
+    ```bash
+    gcloud projects add-iam-policy-binding PROJECT_ID \
+        --member="serviceAccount:SERVICE_ACCOUNT_EMAIL" \
+        --role="roles/secretmanager.secretAccessor"
+    ```
+    Replace `PROJECT_ID` with your Google Cloud project ID and `SERVICE_ACCOUNT_EMAIL` with the email of the service account your Cloud Run service is using.
+
+## Deploy the Application to Cloud Run
+
+Follow these steps to deploy the application to Cloud Run.
+
+### Build and Push the Docker Image
+
+1.  **Enable the Artifact Registry API:**
+
+    ```bash
+    gcloud services enable artifactregistry.googleapis.com
+    ```
+
+2.  **Create an Artifact Registry repository:**
+
+    ```bash
+    gcloud artifacts repositories create REPO_NAME \
+      --repository-format=docker \
+      --location=REGION
+    ```
+
+3.  **Configure Docker to authenticate with Artifact Registry:**
+
+    ```bash
+    gcloud auth configure-docker REGION-docker.pkg.dev
+    ```
+
+4.  **Build the Docker image (replace `mysql` with `postgres` or `sqlserver` as needed):**
+
+    ```bash
+    docker build -t REGION-docker.pkg.dev/PROJECT_ID/REPO_NAME/IMAGE_NAME mysql
+    ```
+
+5.  **Push the Docker image to Artifact Registry:**
+
+    ```bash
+    docker push REGION-docker.pkg.dev/PROJECT_ID/REPO_NAME/IMAGE_NAME
+    ```
+
+### Deploy to Cloud Run
+
+Deploy the container image to Cloud Run using the `gcloud run deploy` command.
+
+
+**Sample Values:**
+*   `SERVICE_NAME`: `my-cloud-run-service`
+*   `REGION`: `us-central1`
+*   `PROJECT_ID`: `my-gcp-project-id`
+*   `REPO_NAME`: `my-artifact-repo`
+*   `IMAGE_NAME`: `my-app-image`
+*   `INSTANCE_CONNECTION_NAME`: `my-gcp-project-id:us-central1:my-instance-name`
+*   `DB_USER`: `my-db-user` (for password-based authentication)
+*   `DB_IAM_USER`: `[email protected]` (for IAM-based authentication)
+*   `DB_NAME`: `my-db-name`
+*   `DB_PASSWORD`: `my-user-pass-secret-name`
+*   `VPC_NETWORK`: `my-vpc-network`
+*   `SUBNET_NAME`: `my-vpc-subnet`
+
+
+**For MySQL and PostgreSQL (Public IP):**
+
+```bash
+gcloud run deploy SERVICE_NAME \
+  --image=REGION-docker.pkg.dev/PROJECT_ID/REPO_NAME/IMAGE_NAME \
+  --set-env-vars=DB_USER=DB_USER,DB_IAM_USER=DB_IAM_USER,DB_NAME=DB_NAME,DB_SECRET_NAME=DB_SECRET_NAME,INSTANCE_CONNECTION_NAME=INSTANCE_CONNECTION_NAME \
+  --region=REGION \
+  --update-secrets=DB_PASSWORD=DB_PASSWORD:latest 
+```
+
+**For MySQL and PostgreSQL (Private IP):**
+
+```bash
+gcloud run deploy SERVICE_NAME \
+  --image=REGION-docker.pkg.dev/PROJECT_ID/REPO_NAME/IMAGE_NAME \
+  --set-env-vars=DB_USER=DB_USER,DB_IAM_USER=DB_IAM_USER,DB_NAME=DB_NAME,DB_SECRET_NAME=DB_SECRET_NAME,INSTANCE_CONNECTION_NAME=INSTANCE_CONNECTION_NAME,IP_TYPE=PRIVATE \
+  --network=VPC_NETWORK \
+  --subnet=SUBNET_NAME \
+  --vpc-egress=private-ranges-only \
+  --region=REGION \
+  --update-secrets=DB_PASSWORD=DB_PASSWORD:latest 
+```
+
+**For SQL Server (Public IP):**
+
+```bash
+gcloud run deploy SERVICE_NAME \
+  --image=REGION-docker.pkg.dev/PROJECT_ID/REPO_NAME/IMAGE_NAME \
+  --set-env-vars=DB_USER=DB_USER,DB_NAME=DB_NAME,DB_SECRET_NAME=DB_SECRET_NAME,INSTANCE_CONNECTION_NAME=INSTANCE_CONNECTION_NAME \
+  --region=REGION \
+  --update-secrets=DB_PASSWORD=DB_PASSWORD:latest 
+```
+
+**For SQL Server (Private IP):**
+
+```bash
+gcloud run deploy SERVICE_NAME \
+  --image=REGION-docker.pkg.dev/PROJECT_ID/REPO_NAME/IMAGE_name \
+  --set-env-vars=DB_USER=DB_USER,DB_NAME=DB_NAME,DB_SECRET_NAME=DB_SECRET_NAME,INSTANCE_CONNECTION_NAME=INSTANCE_CONNECTION_NAME,IP_TYPE=PRIVATE \
+  --network=VPC_NETWORK \
+  --subnet=SUBNET_NAME \
+  --vpc-egress=private-ranges-only \
+  --region=REGION \
+  --update-secrets=DB_PASSWORD=DB_PASSWORD:latest 
+```
+
+> [!NOTE]
+> **`For PSC connections`**
+>
+> To connect to the Cloud SQL instance with PSC connection type, create a PSC endpoint, a DNS zone and DNS record for the instance in the same VPC network as the Cloud Run service and replace the `IP_TYPE` in the deploy command with `PSC`. To configure DNS records, refer to [Connect to an instance using Private Service Connect](https://docs.cloud.google.com/sql/docs/mysql/configure-private-service-connect) guide

samples/cloudrun/mysql/Dockerfile

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+# Use the official lightweight Python image.
+# https://hub.docker.com/_/python
+FROM python:3.12-slim
+
+# Allow statements and log messages to immediately appear in the Knative logs
+ENV PYTHONUNBUFFERED True
+
+# Copy local code to the container image.
+ENV APP_HOME /app
+WORKDIR $APP_HOME
+COPY . .
+
+# Install production dependencies.
+RUN pip install --no-cache-dir -r requirements.txt
+
+# Run the web service on container startup.
+# Use gunicorn for production deployments.
+CMD exec gunicorn --bind :$PORT --workers 1 --threads 8 --timeout 0 main:app

samples/cloudrun/mysql/main.py

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+"""
+Copyright 2025 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
+
+  https://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 os
+import sqlalchemy
+from flask import Flask
+from google.cloud.sql.connector import Connector, IPTypes
+
+# Initialize Flask app
+app = Flask(__name__)
+
+# Connector and SQLAlchemy engines are initialized as None to allow for lazy instantiation.
+#
+# The Connector object is a global variable to ensure that the same connector
+# instance is used across all requests. This prevents the unnecessary creation
+# of new Connector instances, which is inefficient and can lead to connection
+# limits being reached.
+#
+# Lazy instantiation (initializing the Connector and Engine only when needed)
+# allows the Cloud Run service to start up faster, as it avoids performing
+# initialization tasks (like fetching secrets or metadata) during startup.
+connector = None
+iam_engine = None
+password_engine = None
+
+
+# Function to create a database connection using IAM authentication
+def get_iam_connection() -> sqlalchemy.engine.base.Connection:
+    """Creates a database connection using IAM authentication."""
+    instance_connection_name = os.environ["INSTANCE_CONNECTION_NAME"]
+    db_user = os.environ["DB_IAM_USER"]  # IAM service account email
+    db_name = os.environ["DB_NAME"]
+    ip_type_str = os.environ.get("IP_TYPE", "PUBLIC")
+    ip_type = IPTypes[ip_type_str]
+
+    conn = connector.connect(
+        instance_connection_name,
+        "pymysql",
+        user=db_user,
+        db=db_name,
+        ip_type=ip_type,
+        enable_iam_auth=True,
+    )
+    return conn
+
+
+# Function to create a database connection using password-based authentication
+def get_password_connection() -> sqlalchemy.engine.base.Connection:
+    """Creates a database connection using password authentication."""
+    instance_connection_name = os.environ["INSTANCE_CONNECTION_NAME"]
+    db_user = os.environ["DB_USER"]  # Database username
+    db_name = os.environ["DB_NAME"]
+    db_password = os.environ["DB_PASSWORD"]
+    ip_type_str = os.environ.get("IP_TYPE", "PUBLIC")
+    ip_type = IPTypes[ip_type_str]    
+
+    conn = connector.connect(
+        instance_connection_name,
+        "pymysql",
+        user=db_user,
+        password=db_password,
+        db=db_name,
+        ip_type=ip_type,
+    )
+    return conn
+
+
+# This example uses two distinct SQLAlchemy engines to demonstrate two different
+# authentication methods (IAM and password-based) in the same application.
+#
+# In a typical production application, you would generally only need one
+# SQLAlchemy engine, configured for your preferred authentication method.
+# Both engines are defined globally to allow for connection pooling and
+# reuse across requests.
+
+
+def connect_with_password() -> sqlalchemy.engine.base.Connection:
+    """Initializes the connector and password engine if necessary, then returns a connection."""
+    global connector, password_engine
+
+    if connector is None:
+        connector = Connector(refresh_strategy="lazy")
+
+    if password_engine is None:
+        password_engine = sqlalchemy.create_engine(
+            "mysql+pymysql://",
+            creator=get_password_connection,
+        )
+
+    return password_engine.connect()
+
+
+def connect_with_iam() -> sqlalchemy.engine.base.Connection:
+    """Initializes the connector and IAM engine if necessary, then returns a connection."""
+    global connector, iam_engine
+
+    if connector is None:
+        connector = Connector(refresh_strategy="lazy")
+
+    if iam_engine is None:
+        iam_engine = sqlalchemy.create_engine(
+            "mysql+pymysql://",
+            creator=get_iam_connection,
+        )
+
+    return iam_engine.connect()
+
+
+@app.route("/")
+def password_auth_index():
+    try:
+        with connect_with_password() as conn:
+            result = conn.execute(sqlalchemy.text("SELECT 1")).fetchall()
+            return f"Database connection successful (password authentication), result: {result}"
+    except Exception as e:
+        return f"Error connecting to the database (password authentication)", 500
+
+
+@app.route("/iam")
+def iam_auth_index():
+    try:
+        with connect_with_iam() as conn:
+            result = conn.execute(sqlalchemy.text("SELECT 1")).fetchall()
+            return f"Database connection successful (IAM authentication), result: {result}"
+    except Exception as e:
+        return f"Error connecting to the database (IAM authentication)", 500
+
+if __name__ == "__main__":
+    app.run(host="0.0.0.0", port=int(os.environ.get("PORT", 8080)))

samples/cloudrun/mysql/requirements.txt

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+cloud-sql-python-connector[pymysql]
+sqlalchemy
+Flask
+gunicorn
+google-cloud-secret-manager

samples/cloudrun/postgres/Dockerfile

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+# Use the official lightweight Python image.
+# https://hub.docker.com/_/python
+FROM python:3.12-slim
+
+# Allow statements and log messages to immediately appear in the Knative logs
+ENV PYTHONUNBUFFERED True
+
+# Copy local code to the container image.
+ENV APP_HOME /app
+WORKDIR $APP_HOME
+COPY . .
+
+# Install production dependencies.
+RUN pip install --no-cache-dir -r requirements.txt
+
+# Run the web service on container startup.
+# Use gunicorn for production deployments.
+CMD exec gunicorn --bind :$PORT --workers 1 --threads 8 --timeout 0 main:app