Throughout the next few sub-sections, we will describe some of the critical facets of GAE, starting with application versioning.
Understanding App Engine features
Application versioning
GAE uses a configuration file to manage application versions to deploy. The configuration file for the runtime selected, for example, app.yaml for Python deployments, contains the version ID associated with your application. In addition to the version, an application default denotes the primary instance to the system.
Each application version deployed will maintain its distinct URL so that the developer can view multiple versions at the same time. Similarly, releases can be upgraded or rolled back depending on the deployment scheme selected...