Google Cloud Platform for Developers

Deployment behavior

By default, once a new version of a service has been deployed, all traffic will be migrated from existing versions. For production systems, this is likely not an ideal behavior. Developers may desire to validate the new version before cutting traffic over, or to utilize a more complex strategy such as canary testing. For these cases, gcloud app deploy accepts the optional --no-promote flag. When provided, App Engine will not modify traffic, allowing a previous version of the service to handle all requests. Developers can then utilize the versioned URL to interact with the service without affecting end users.

The default behavior for previous versions of a service is to remain running. For services in the standard environment ...