CODEWITHSUNDEEP
pythongoogle-app-enginetestingdevelopment-environment
0x24a537r9
0x24a537r9

Reputation: 990

Python App Engine debug/dev mode

I'm working on an App Engine project (Python) where we'd like to make certain changes to the app's behavior when debugging/developing (most often locally). For example, when debugging, we'd like to disable our rate-limiting decorators, turn on the debug param in the WSGIApplication, maybe add some asserts.

As far as I can tell, App Engine doesn't naturally have any concept of a global dev-mode or debug-mode, so I'm wondering how best to implement such a mode. The options I've been able to come up with so far:

  1. Use google.appengine.api.app_identity.get_default_version_hostname() to get the hostname and check if it begins with localhost. This seems... unreliable, and doesn't allow for using the debug mode in a deployed app instance.

  2. Use os.environ.get('APPLICATION_ID') to get the application id, which according to this page is automatically prepended with dev~ by the development server. Worryingly, the very source of this information is in a box warning:

    Do not get the App ID from the environment variable. The development server simulates the production App Engine service. One way in which it does this is to prepend a string (dev~) to the APPLICATION_ID environment variable, which is similar to the string prepended in production for applications using the High Replication Datastore. You can modify this behavior with the --default_partition flag, choosing a value of "" to match the master-slave option in production. Google recommends always getting the application ID using get_application_id, as described above.

    Not sure if this is an acceptable use of the environment variable. Either way it's probably equally hacky, and suffers the same problem of only working with a locally running instance.

  3. Use a custom app-id for development (locally and deployed), use the -A flag in dev_appserver.py, and use google.appengine.api.app_identity.get_application_id() in the code. I don't like this for a number of reasons (namely having to have two separate app engine projects).

  4. Use a dev app engine version for development and detect with os.environ.get('CURRENT_VERSION_ID').split('.')[0] in code. When deployed this is easy, but I'm not sure how to make dev_appserver.py use a custom version without modifying app.yaml. I suppose I could sed app.yaml to a temp file in /tmp/ with the version replaced and the relative paths resolved (or just create a persistent dev-app.yaml), then pass that into dev_appserver.py. But that seems also kinda dirty and prone to error/sync issues.

Am I missing any other approaches? Any considerations I failed to acknowledge? Any other advice?

Upvotes: 4

Views: 1396

Answers (1)

Jesse
Jesse

Reputation: 8393

In regards to "detecting" localhost development we use the following in our applications settings / config file.

IS_DEV_APPSERVER = 'development' in os.environ.get('SERVER_SOFTWARE', '').lower()

That used in conjunction with the debug flag should do the trick for you.

Upvotes: 3

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