App Engine: Application Versioning

App Engine permits you to deploy multiple versions of your app and have them running side-by-side. All the versions share the samedatastore and memcache, but they run in separate instances and have different URLs. Your ‘live’ version always serves off yourapp.appspot.com as well as any domains you have mapped, but all your app’s versions are accessible at version.latest.yourapp.appspot.com. Multiple versions are particularly useful for testing a new release in a production environment, on real data, before making it available to all your users.