Splitting Traffic between App Engine Versions
If you have more than one version of an application running, you can split traffic between the versions. App Engine provides three ways to split traffic: by IP address, by HTTP cookie, and by random selection. IP address splitting provides some stickiness, so a client is always routed to the same split, at least as long as the IP address does not change. HTTP cookies are useful when you want to assign users to versions. Random selection is useful when you want to evenly distribute workload.
When using IP address splitting, App Engine creates a hash, that is, a number generated based on an input string between 0 and 999, using the IP address of each version. This can create problems if users change IP address, such as if they start working with the app in the office and then switch to a network in a coffee shop. If state information is maintained in a version, it may not be available after an IP address change.
The preferred way to split...
