Rollouts

Percentage Rollouts

FlagSync uses a deterministic hashing algorithm to evaluate percentage rollouts, ensuring users receive the same variant on each evaluation.

Define Rollout

Set percentage distributions in the dashboard (e.g., 25% “Enabled”, 75% “Disabled”).

Hash Inputs

Hash the user context key (e.g., user ID, email, attributes) and flag seed (unique per flag and environment).

import { FlagSyncFactory } from '@flagsync/js-sdk';

const factory = FlagSyncFactory({
  sdkKey: 'your-sdk-key',
  core: { key: 'user123' }
});

Normalize and Bucket

Normalize the hash to 0-99, placing users in buckets.

e.g., a normalized value of 16 falls in the 0-24 bucket, serving “Enabled” at 25%.

Reshuffle

In the dashboard, you can reshuffle an active percentage rollout, changing the flag seed and reassigning users to new buckets.

Fallback

If no rollout applies, the default “on” variant is served.

Return to Flag Evaluation: Overview for the full flow.

Explore more about flag evaluation and SDKs: