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Migrating from App Engine Blobstore to Cloud Storage (Module 16)

Posted by Wesley Chun (@wescpy), Developer Advocate, Google Cloud

Serverless Migration Station video demonstrated how one can add use of the App Engine’s Blobstore service to a pattern Python 2 App Engine app, kicking off the primary of a 2-part sequence on migrating away from Blobstore. In at this time’s Module 16 video, we full this journey, arriving at Cloud Storage. Shifting away from proprietary App Engine providers like Blobstore makes apps extra moveable, giving them sufficient flexibility to:

Displaying App Engine customers how one can migrate to Cloud Storage

As described beforehand, a Blobstore for Python 2 dependency on webapp made the Module 15 content material extra simple to implement if it was nonetheless utilizing webapp2. To fully modernize this app right here in Module 16, the next migrations must be carried out:

  • Migrate from webapp2 (and webapp) to Flask
  • Migrate from App Engine NDB to Cloud NDB
  • Migrate from App Engine Blobstore to Cloud Storage
  • Migrate from Python 2 to Python (2 and) 3

Performing the migrations

Previous to modifying the applying code, quite a lot of configuration updates must be made. Updates making use of solely to Python 2 function a “Py2” designation whereas these migrating to Python 3 will see “Py3” annotations.

  1. Take away the built-in Jinja2 library from app.yaml—Jinja2 already comes with Flask, so take away use of the older built-in model which can probably battle with the up to date Flask model you are utilizing. (Py2)
  2. Use of Cloud consumer libraries (resembling these for Cloud NDB and Cloud Storage) require a pair of built-in libraries, grpcio and setuptools, so add these to app.yaml (Py2)
  3. Take away every little thing in app.yaml apart from a sound runtime (Py3)
  4. Add Cloud NDB and Cloud Storage consumer libraries to necessities.txt (Py2 & Py3)
  5. Create an supporting each built-in (these in app.yaml) and non built-in (these in necessities.txt) libraries used (Py2)

The Module 15 app already migrated away from webapp2‘s (Django) templating system to Jinja2. That is helpful when migrating to Flask as a result of Jinja2 is Flask’s default template system. Switching from App Engine NDB to Cloud NDB is pretty simple because the latter was designed to be principally appropriate with the unique. The one change seen on this pattern app is to maneuver Datastore calls into Python with blocks.

Probably the most vital adjustments happen when transferring the add and obtain handlers from webapp to Cloud Storage. The video and corresponding codelab go extra in-depth into the required adjustments, however in abstract, these are the updates required in the principle software:

  1. webapp2 is changed by Flask. As a substitute of utilizing the older built-in model of Jinja2, use the model that comes with Flask.
  2. App Engine Blobstore and NDB are changed by Cloud NDB and Cloud Storage, respectively.
  3. The webapp Blobstore handler performance is changed by a mixture of the io commonplace library module plus elements from Flask and Werkzeug. Moreover, the handler courses and strategies are changed by Flask capabilities.
  4. The principle handler class and corresponding GET and POST strategies are all changed by a single Flask operate.

The outcomes

With all of the adjustments applied, the unique Module 15 app nonetheless operates identically in Module 16, beginning with a type requesting a go to artifact adopted by probably the most recents visits web page:

The pattern app’s artifact immediate web page

The pattern app’s most up-to-date visits web page.

The one distinction is that 4 migrations have been accomplished the place the entire “infrastructure” is now taken care of by non-App Engine legacy providers. Moreover, the Module 16 app might be both a Python 2 or 3 app. So far as the end-user is worried, “nothing occurred.”

Migrating pattern app from App Engine Blobstore to Cloud Storage


Module 16 featured 4 completely different migrations, modernizing the Module 15 app from utilizing App Engine legacy providers like NDB and Blobstore to Cloud NDB and Cloud Storage, respectively. Whereas we advocate customers transfer to the most recent choices from Google Cloud, migrating from Blobstore to Cloud Storage is not required, and do you have to choose to take action, can do it by yourself timeline. Along with at this time’s video, you should definitely take a look at the Module 16 codelab which leads you step-by-step by the migrations mentioned.

In Fall 2021, the App Engine staff prolonged assist of lots of the bundled providers to 2nd technology runtimes (which have a 1st technology runtime), that means you might be now not required emigrate to Cloud Storage when porting your app to Python 3. You’ll be able to proceed utilizing Blobstore in your Python 3 app as long as you retrofit the code to entry bundled providers from next-generation runtimes.

In the event you’re utilizing different App Engine legacy providers you should definitely take a look at the opposite Migration Modules on this sequence. All Serverless Migration Station content material (codelabs, movies, supply code [when available]) may be accessed at its open supply repo. Whereas our content material initially focuses on Python customers, the Cloud staff is engaged on masking different language runtimes, so keep tuned. For added video content material, take a look at our broader Serverless Expeditions sequence.



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