App Engine Migration Guide
This is repository is a guide for developers needing to move the App Engine Standard for Python 2.7 apps to App Engine Standard for Python 3.8. Many of the steps here would also be helpful if the target environment were another Python 3.x system.
Community contributions of examples of migration challenges people have encountered and overcome are welcome. See CONTRIBUTING.md for how to offer a contribution. In a nutshell, you should fork this repository, add your examples, and then submit a pull request. We will review the request and ask you to sign a Contributor License Agreement before merging the it.
Contributing changes
- See CONTRIBUTING.md
Licensing
- See LICENSE
Planning for migration
Migrating an app from App Engine Standard for Python 2.7 system to App Engine Standard for Python 3.8 necessarily involves making the code compliant with Python 3.8. It is possible to do that while having the code continue to run properly under Python 2.7. There are many guides available on how to do this, such as the standard Python documentation for Porting Python 2 Code to Python 3. This guide defers to those other sources on how to make such needed changes. Instead, this guide focuses on the specific App Engine changes that must be addressed.
The first step in migrating your app is to identify the features it uses that are not available in the current runtime. These may include:
- An application framework, such as webapp or webapp2, that cannot run under Python 3.x.
- Bundled libraries that are being used:
- Blobstore
- Datastore
- Images
- Logging
- Memcache
- Task queue
- URL fetch
- User authentication
Developers should identify which of these issues apply to their app, and address them one at a time in a way that continues to work under Python 2 in the Gen 1 environment, but will also work once the app is moved to Python 3 in the Gen 2 environment. Migration strategies and software samples are provided for each of these areas in the following sections.