Django tutorial for App Engine is broken

[jackwotherspoon]

The section in the following App Engine quickstart references a variable in the code USE_CLOUD_SQL_AUTH_PROXY that only works locally and not when deploying to App Engine.

# Use django-environ to parse the connection string
DATABASES = {"default": env.db()}

# If the flag as been set, configure to use proxy
if os.getenv("USE_CLOUD_SQL_AUTH_PROXY", None):
    DATABASES["default"]["HOST"] = "127.0.0.1"
    DATABASES["default"]["PORT"] = 5432

The flag sets the host and port of the database connection to expect a local TCP connection. This works for the local deployment of the app as the quickstart prompts the user to run the Cloud SQL Auth Proxy locally configured with TCP.

However, if this flag is set when deploying the code to App Engine it breaks the sample. App Engine is automatically configured with the Cloud SQL Auth Proxy but the Proxy in a serverless environment is configured to use Unix sockets not a TCP connection.

The .env file used in the quickstart sets the database connection to use the proper Unix socket configuration (/cloudsql/PROJECT_ID:REGION:INSTANCE_NAME) in a previous step.

echo DATABASE_URL=postgres://DATABASE_USERNAME:DATABASE_PASSWORD@//cloudsql/PROJECT_ID:REGION:INSTANCE_NAME/DATABASE_NAME > .env

However, the use of the USE_CLOUD_SQL_AUTH_PROXY flag overrides this proper value and breaks the sample.

Noted by a SO user: https://stackoverflow.com/questions/77164817/django-app-on-google-app-engine-not-connecting-to-google-cloud-sql/77172777

[glasnt]

if this flag is set when deploying the code to App Engine it breaks the sample.

Correct. The USE_CLOUD_SQL_AUTH_PROXY flag would break in prod, but it should never be set in prod.

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Per the proxy docs, setting up the proxy to ./cloud-sql-proxy INSTANCE_CONNECTION_NAME yields Listening on 127.0.0.1:5432 for INSTANCE_CONNECTION_NAME.

The helper package in this deployment, django-environ, allows you to use a .env file to load environment variables. This is useful when there are many variables that need to be loaded. The env.db() helper method also allows you to set a database connection string (DATABASE_URL), rather than separate configurations for username, password, host, etc., splitting them up and setting them in the DATABASE[default] setting.

Therefore, when using the local proxy, the hostname changes. In this sample, the USE_CLOUD_SQL_AUTH_PROXY flag is used to help make those changes to the DATABASE, specifically changing the HOST and PORT.

Setting USE_CLOUD_SQL_AUTH_PROXY as an environment variable in the local terminal shouldn't affect App Engine. The only way I can see this might have happened is if USE_CLOUD_SQL_AUTH_PROXY ended up in the .env, and was therefore in play in production.

Unless I'm otherwise misunderstanding the problem, this sample works as intended.

[jackwotherspoon]

@glasnt I find the naming of USE_CLOUD_SQL_AUTH_PROXY variable quite confusing and it seems users are also finding it confusing.

If I was reading this section of the docs, it does not explicitly mention that the var should only be set for using the Proxy with a local TCP connection.

The section says "If you set the USE_CLOUD_SQL_AUTH_PROXY, the DATABASES setting is changed to infer use of the Cloud SQL Auth Proxy." which is not 100% accurate (setting the env var to False infers a Unix socket connection with the Cloud SQL Auth Proxy by default). If I am a new user reading this and wanting to use the Cloud SQL Auth Proxy with App Engine I would assume I need to set the env var to True.

I wonder if we can maybe make this env var more clear for users. Really the env var is for toggling between Unix vs TCP connection type for the Cloud SQL Auth Proxy.

[glasnt]

After discussion with @jackwotherspoon, I'll update the Understanding the Code - Database connection description to better reflect what this setting is doing in local setups.