Split Rollouts

How split by percentage works

CloudBees Feature Management utilizes a distributed algorithm. This algorithm is similar to tossing a coin on the device. But once a coin is tossed the result is consistent for a feature flag.

Split by percentage only works for string and number type flags once you have defined feature-flags:feature-flag-setting.adoc#_feature_flag_variations.

How the algorithm works

The client side SDK generates a UUID (called rox.distinct_id) and serializes it on the device.
Every feature flag has its own seed to make sure there isn’t a statistical bias between 2 feature flags.
The SDK takes the seed and distinct_id and runs a hash function that is mapped to a double number from 0-1.

If you select a 50% split, for example, then we are checking if the hash result is smaller the 0.5.

Implication of the algorithm

The result is consistent, every time a user opens the app they will get the same result (unless you changed percentage).
If you increase percentage, all your existing users that already received true value will keep getting it.
If you decrease percentage, some of your users will stop receiving a true value even if they have received one before.
A single user’s place in the bucket is different in every feature flag (so your users will not always get a new feature).

Override distinct_id with user id

You can choose to override the distinct_id. This is important for 2 reasons:

Having a consistent cross platform behavior for split
Having a consistent experience for your users of backend SDK