refactor Cloud SQL SQL Server samples

* use environment varialbe for proxy connection hostname over hardcoding it
* make all environment variables required
* include instructions in README for running locally on Windows
* make code structure consistent with PostgreSQL and MySQL samples

Author: Saketram Durbha

cloud-sql/sql-server/sqlalchemy/README.md

@@ -31,29 +31,48 @@
 [instructions](https://cloud.google.com/sql/docs/postgres/connect-external-app#4_if_required_by_your_authentication_method_create_a_service_account).
 Download a JSON key to use to authenticate your connection. 
 
-1. Use the information noted in the previous steps:
+## Running locally
+To run this application locally, download and install the `cloud_sql_proxy` by
+following the instructions [here](https://cloud.google.com/sql/docs/mysql/sql-proxy#install). 
+
+### Linux / MacOS
+Use these terminal commands to initialize environment variables:
 ```bash
 export GOOGLE_APPLICATION_CREDENTIALS=/path/to/service/account/key.json
 export CLOUD_SQL_CONNECTION_NAME='<MY-PROJECT>:<INSTANCE-REGION>:<INSTANCE-NAME>'
 export DB_USER='my-db-user'
 export DB_PASS='my-db-pass'
 export DB_NAME='my_db'
+export DB_HOST='127.0.0.1:1433'
 ```
 Note: Saving credentials in environment variables is convenient, but not secure - consider a more
 secure solution such as [Cloud KMS](https://cloud.google.com/kms/) to help keep secrets safe.
 
-## Running locally
+Then, use the following command to start the proxy in the background using TCP:
+```bash
+./cloud_sql_proxy -instances=${CLOUD_SQL_CONNECTION_NAME}=tcp:1433 sqlserver -u ${DB_USER} --host 127.0.0.1 &
+```
 
-To run this application locally, download and install the `cloud_sql_proxy` by
-following the instructions [here](https://cloud.google.com/sql/docs/mysql/sql-proxy#install). 
+### Windows / PowerShell
+Use these PowerShell commands to initialize environment variables:
+```powershell
+$env:GOOGLE_APPLICATION_CREDENTIALS="<CREDENTIALS_JSON_FILE>"
+$env:CLOUD_SQL_CONNECTION_NAME="<MY-PROJECT>:<INSTANCE-REGION>:<INSTANCE-NAME>"
+$env:DB_USER="my-db-user"
+$env:DB_PASS="my-db-pass"
+$env:DB_NAME="my_db"
+$env:DB_HOST="127.0.0.1:1433"
+```
+Note: Saving credentials in environment variables is convenient, but not secure - consider a more
+secure solution such as [Cloud KMS](https://cloud.google.com/kms/) to help keep secrets safe.
 
-Then, use the following command to start the proxy in the
-background using TCP:
-```bash
-./cloud_sql_proxy -instances=${CLOUD_SQL_CONNECTION_NAME}=tcp:1433 sqlserver -u ${DB_USER} --host 127.0.0.1
+Then use this command to launch the proxy in a separate PowerShell session:
+```powershell
+Start-Process -filepath "C:\<path to proxy exe>" -ArgumentList "-instances=<MY-PROJECT>:<INSTANCE-REGION>:<INSTANCE-NAME>=tcp:1433 -credential_file=<CREDENTIALS_JSON_FILE>"
 ```
 
-Next, setup install the requirements into a virtual enviroment:
+### Testing the application
+Next, setup a virtual environment and install the application's requirements:
 ```bash
 virtualenv --python python3 env
 source env/bin/activate

cloud-sql/sql-server/sqlalchemy/app.yaml

@@ -21,8 +21,7 @@ env_variables:
   DB_USER: <your-username>
   DB_PASS: <your-password>
   DB_NAME: <your-db-name>
-  # Whether the app is deployed or running locally
-  DEPLOYED: true
+  DB_HOST: 172.17.0.1:<PORT>
 
 beta_settings:
-  cloud_sql_instances: <project-name>:<region-name>:<instance-name>=tcp:1433
+  cloud_sql_instances: <project-name>:<region-name>:<instance-name>=tcp:<PORT>

cloud-sql/sql-server/sqlalchemy/main.py

@@ -29,60 +29,68 @@
 
 logger = logging.getLogger()
 
-# [START cloud_sql_server_sqlalchemy_create]
-# Remember - storing secrets in plaintext is potentially unsafe. Consider using
-# something like https://cloud.google.com/kms/ to help keep secrets secret.
-db_user = os.environ.get("DB_USER")
-db_pass = os.environ.get("DB_PASS")
-db_name = os.environ.get("DB_NAME")
-
-# When deployed to GAE Flex for TCP, use "172.17.0.1" to connect
-host = "172.17.0.1" if os.environ.get("DEPLOYED") else "127.0.0.1"
-
-# The SQLAlchemy engine will help manage interactions, including automatically
-# managing a pool of connections to your database
-db = sqlalchemy.create_engine(
-    # Equivalent URL:
-    # mssql+pyodbc://<db_user>:<db_pass>@/<host>:<port>/<db_name>?driver=ODBC+Driver+17+for+SQL+Server
-    sqlalchemy.engine.url.URL(
-        "mssql+pyodbc",
-        username=db_user,
-        password=db_pass,
-        database=db_name,
-        host=host,
-        port=1433,
-        query={"driver": "ODBC Driver 17 for SQL Server"},
-    ),
-    # ... Specify additional properties here.
-    # [START_EXCLUDE]
-    # [START cloud_sql_server_sqlalchemy_limit]
-    # Pool size is the maximum number of permanent connections to keep.
-    pool_size=5,
-    # Temporarily exceeds the set pool_size if no connections are available.
-    max_overflow=2,
-    # The total number of concurrent connections for your application will be
-    # a total of pool_size and max_overflow.
-    # [END cloud_sql_server_sqlalchemy_limit]
-    # [START cloud_sql_server_sqlalchemy_backoff]
-    # SQLAlchemy automatically uses delays between failed connection attempts,
-    # but provides no arguments for configuration.
-    # [END cloud_sql_server_sqlalchemy_backoff]
-    # [START cloud_sql_server_sqlalchemy_timeout]
-    # 'pool_timeout' is the maximum number of seconds to wait when retrieving a
-    # new connection from the pool. After the specified amount of time, an
-    # exception will be thrown.
-    pool_timeout=30,  # 30 seconds
-    # [END cloud_sql_server_sqlalchemy_timeout]
-    # [START cloud_sql_server_sqlalchemy_lifetime]
-    # 'pool_recycle' is the maximum number of seconds a connection can persist.
-    # Connections that live longer than the specified amount of time will be
-    # reestablished
-    pool_recycle=1800,  # 30 minutes
-    # [END cloud_sql_server_sqlalchemy_lifetime]
-    echo=True  # debug
-    # [END_EXCLUDE]
-)
-# [END cloud_sql_server_sqlalchemy_create]
+
+def init_tcp_connection_engine():
+    # [START cloud_sql_server_sqlalchemy_create_tcp]
+    # Remember - storing secrets in plaintext is potentially unsafe. Consider using
+    # something like https://cloud.google.com/kms/ to help keep secrets secret.
+    db_user = os.environ["DB_USER"]
+    db_pass = os.environ["DB_PASS"]
+    db_name = os.environ["DB_NAME"]
+
+    # Extract host and port from environment variable DB_HOST
+    host_args = os.environ["DB_HOST"].split(":")
+    host, port = host_args[0], int(host_args[1])
+
+    # The SQLAlchemy engine will help manage interactions, including automatically
+    # managing a pool of connections to your database
+    pool = sqlalchemy.create_engine(
+        # Equivalent URL:
+        # mssql+pyodbc://<db_user>:<db_pass>@/<host>:<port>/<db_name>?driver=ODBC+Driver+17+for+SQL+Server
+        sqlalchemy.engine.url.URL(
+            "mssql+pyodbc",
+            username=db_user,
+            password=db_pass,
+            database=db_name,
+            host=host,
+            port=port,
+            query={"driver": "ODBC Driver 17 for SQL Server"},
+        ),
+        # ... Specify additional properties here.
+        # [START_EXCLUDE]
+        # [START cloud_sql_server_sqlalchemy_limit]
+        # Pool size is the maximum number of permanent connections to keep.
+        pool_size=5,
+        # Temporarily exceeds the set pool_size if no connections are available.
+        max_overflow=2,
+        # The total number of concurrent connections for your application will be
+        # a total of pool_size and max_overflow.
+        # [END cloud_sql_server_sqlalchemy_limit]
+        # [START cloud_sql_server_sqlalchemy_backoff]
+        # SQLAlchemy automatically uses delays between failed connection attempts,
+        # but provides no arguments for configuration.
+        # [END cloud_sql_server_sqlalchemy_backoff]
+        # [START cloud_sql_server_sqlalchemy_timeout]
+        # 'pool_timeout' is the maximum number of seconds to wait when retrieving a
+        # new connection from the pool. After the specified amount of time, an
+        # exception will be thrown.
+        pool_timeout=30,  # 30 seconds
+        # [END cloud_sql_server_sqlalchemy_timeout]
+        # [START cloud_sql_server_sqlalchemy_lifetime]
+        # 'pool_recycle' is the maximum number of seconds a connection can persist.
+        # Connections that live longer than the specified amount of time will be
+        # reestablished
+        pool_recycle=1800,  # 30 minutes
+        # [END cloud_sql_server_sqlalchemy_lifetime]
+        echo=True  # debug
+        # [END_EXCLUDE]
+    )
+    # [END cloud_sql_server_sqlalchemy_create_tcp]
+
+    return pool
+
+
+db = init_tcp_connection_engine()
 
 
 @app.before_first_request