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


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

    Introduction and background

    The latest 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 right this moment’s Module 16 video, we full this journey, arriving at Cloud Storage. Transferring away from proprietary App Engine companies like Blobstore makes apps extra moveable, giving them sufficient flexibility to:

    Exhibiting 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 easy to implement if it was nonetheless utilizing webapp2. To utterly modernize this app right here in Module 16, the next migrations ought to 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, a wide range of configuration updates have to 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 modern Flask model you are utilizing. (Py2)
    2. Use of Cloud shopper libraries (comparable to 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 the whole lot in app.yaml aside from a legitimate runtime (Py3)
    4. Add Cloud NDB and Cloud Storage shopper libraries to necessities.txt (Py2 & Py3)
    5. Create an appengine_config.py 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 easy 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.

    Essentially the most important 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 utility:

    1. webapp2 is changed by Flask. As an alternative 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 normal library module plus elements from Flask and Werkzeug. Moreover, the handler lessons and strategies are changed by Flask features.
    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 essentially 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 companies. Moreover, the Module 16 app may very well be both a Python 2 or 3 app. So far as the end-user is anxious, “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 companies like NDB and Blobstore to Cloud NDB and Cloud Storage, respectively. Whereas we suggest customers transfer to the most recent choices from Google Cloud, migrating from Blobstore to Cloud Storage is not required, and must you choose to take action, can do it by yourself timeline. Along with right this moment’s video, remember to take a look at the Module 16 codelab which leads you step-by-step by way of the migrations mentioned.

    In Fall 2021, the App Engine staff prolonged help of most of the bundled companies to 2nd era runtimes (which have a 1st era runtime), that means you’re not required emigrate to Cloud Storage when porting your app to Python 3. You possibly can proceed utilizing Blobstore in your Python 3 app as long as you retrofit the code to entry bundled companies from next-generation runtimes.

    In the event you’re utilizing different App Engine legacy companies remember to take a look at the opposite Migration Modules on this sequence. All Serverless Migration Station content material (codelabs, movies, supply code [when available]) might 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 extra video content material, take a look at our broader Serverless Expeditions sequence.


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