The most important use of versions is to test new software candidates before launching
them to all of your users. You can test a nondefault version yourself by addressing
its version URL, while all of your live traffic goes to the default version. But what if
you want to test a new candidate with a percentage of your actual users? For that, you
use traffic splitting.
With traffic splitting enabled, App Engine identifies the users of your app, partitions
them according to percentages that you specify, and routes their requests to the versions
that correspond to their partitions. You can then analyze the logs of each version
separately to evaluate the candidate for issues and other data.
To enable traffic splitting, go to the Versions panel. If you have more than one module,
select the module whose traffic you want to split. (We’ll look at modules in more
depth in Chapter 5.) Click the “Enable traffic splitting” button, and set the parameters
for the traffic split in the dialog that opens.The dialog asks you to decide whether users should be identified by IP address or by a
cookie. Splitting by cookie is likely to be more accurate for users with browser clients,
and accommodates cases where a single user might appear to be sending requests
from multiple IP addresses. If the user is not using a client that supports cookies, or
you otherwise don’t want to use them, you can split traffic by IP address. The goal is
for each user to always be assigned the same partition throughout a session with multiple
requests, so clients don’t get confused talking to multiple versions, and your
experiment gets consistent results.
Traffic splitting occurs with requests sent to the main URL for the app or module.
Requests for the version-specific URLs bypass traffic splitting.
T