Posted by Wesley Chun (@wescpy), Developer Advocate, Google Cloud
Introduction and background
The Serverless Migration Station sequence is aimed toward serving to builders modernize their apps operating certainly one of Google Cloud’s serverless platforms. The previous (Migration Module 18) video demonstrates tips on how to add use of App Engine’s Activity Queue pull duties service to a Python 2 App Engine pattern app. As we speak’s Module 19 video picks up from the place that leaves off, migrating that pull process utilization to Cloud Pub/Sub.
Shifting away from proprietary App Engine providers like Activity Queue makes apps extra transportable, giving them sufficient flexibility to:
Understanding the migrations
Module 19 consists of implementing three completely different migrations on the Module 18 pattern app:
- Migrate from App Engine NDB to Cloud NDB
- Migrate from App Engine Activity Queue pull duties to Cloud Pub/Sub
- Migrate from Python 2 to Python (2 and) 3
The NDB to Cloud NDB migration is an identical to the Module 2 migration content material, so it is not coated in-depth in Module 19. The unique app was designed to be Python 2 and three suitable, so there is no work there both. Module 19 boils down to 3 key updates:
- Setup: Allow APIs and create Pub/Sub Subject & Subscription
- How work is created: Publish Pub/Sub messages as an alternative of including pull duties
- How work is processed: Pull messages as an alternative of leasing duties
Except for these bodily modifications, a key hurdle to beat is knowing the variations in terminology between pull duties and Pub/Sub. The next chart makes an attempt to demystify this so builders can extra simply grasp how they differ:
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| Terminology variations between App Engine pull duties and Cloud Pub/Sub |
Reflecting the chart, these variations will be summarized like this:
- With Pull Queues, work is created in pull queues whereas work is distributed to Pub/Sub matters
- Activity Queue pull duties are referred to as messages in Pub/Sub
- With Activity Queues, staff entry pull duties; with Pub/Sub, subscribers obtain messages
- Leasing a pull process is similar as pulling a message from a Pub/Sub subject by way of a subscription
- Deleting a process from a pull queue once you’re carried out is analogous to efficiently acknowledging a Pub/Sub message
The video walks builders by way of the terminology in addition to the code modifications described above. Beneath is pseudocode implementing the important thing modifications to the primary software (new or up to date strains of code bolded):
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| Migration from App Engine Activity Queue pull duties to Cloud Pub/Sub |
Observe how many of the code, particularly app operations and knowledge fashions are left comparatively unchanged. The one seen modifications are switching from App Engine NDB and Activity Queue to Cloud NDB and Pub/Sub. Full variations of the app earlier than and after making the modifications will be discovered within the Module 18 and Module 19 repo folders, respectively. Along with the video, make sure to try the Module 19 codelab which leads you step-by-step by way of the migrations mentioned.
Wrap-up
Module 19 includes a migration of App Engine pull duties to Cloud Pub/Sub, however builders ought to observe that Pub/Sub itself just isn’t primarily based on pull duties. It’s a fully-featured asynchronous, scalable messaging service that has many extra options than the pull performance offered by Activity Queue. For instance, Pub/Sub has different options like streaming to BigQuery and push performance. Pub/Sub push operates otherwise than Activity Queue push duties, therefore why we advocate push duties be migrated to Cloud Duties as an alternative (see Module 8). For extra info on all of its options, see the Pub/Sub documentation. As a result of Cloud Duties does not assist pull performance, we flip to Pub/Sub as an alternative for pull process customers.
Whereas we advocate customers transfer to the newest choices from Google Cloud, neither of these migrations are required, and do you have to decide to take action, can do them by yourself timeline. In Fall 2021, the App Engine crew prolonged assist of most of the bundled providers to 2nd era runtimes (which have a 1st era runtime), that means you do not have emigrate to standalone Cloud providers earlier than porting your app to Python 3. You’ll be able to proceed utilizing Activity Queue in Python 3 as long as you retrofit your code to entry bundled providers from next-generation runtimes.
Should you’re utilizing different App Engine legacy providers make sure to try the opposite Migration Modules on this sequence. All Serverless Migration Station content material (codelabs, movies, supply code [when available]) will be accessed at its open supply repo. Whereas our content material initially focuses on Python customers, the Cloud crew is engaged on protecting different language runtimes, so keep tuned. For added video content material, try our broader Serverless Expeditions sequence.
