Progressive delivery

Release a feature to a small audience first, watch how it behaves, and widen it in steps until everyone has it. Each step is a reviewed change to one number.

This page rolls out checkout from the Quick start: first to some Dutch users, then all of them, then everyone else.

Start with one country#

Begin with 10% of users in the netherlands segment, which the default project already has:

description: Checkout redesign
bucketBy: userId
rules:
  - key: netherlands
    conditions: netherlands
    percentage: 10

Users outside the Netherlands match no rule, so they do not get the feature.

Widen it in steps#

Before the first step, agree what you will watch at each one, such as checkout errors and completed orders, and what makes you stop. Each later pull request is then a routine call rather than a debate.

Once the numbers look right, raise the percentage in a new pull request. When Dutch users are at 100%, add a rule for everyone else:

description: Checkout redesign
bucketBy: userId
rules:
  - key: netherlands
    conditions: netherlands
    percentage: 100
  - key: everyone
    conditions: '*'
    percentage: 25

Every user has a fixed bucket for checkout, so raising a percentage only ever adds users. Nobody who had the new checkout loses it. Four users get these results at each step:

Their buckets for checkout are 89.3, 73.5, 15.5 and 38.5, so each switches on once a rule that matches them reaches that percentage.

Keep the feature key, bucketBy and the users' IDs the same throughout, or the buckets change. Lowering a percentage switches the feature off for the users above the new value, so do it only to roll back.

Check each step#

Before each change merges, test the boundary of the new percentage. At 25%, a German user just below 25 is in and one just above is out:

feature: checkout
assertions:
  - description: Everyone else is in below 25
    at: 24
    context:
      country: de
    expectedToBeEnabled: true
  - description: Everyone else is out above 25
    at: 26
    context:
      country: de
    expectedToBeEnabled: false

Then evaluate the users you care about:

npx featurevisor evaluate \
  --feature=checkout \
  --context='{"userId": "user-5", "country": "de"}' \
  --explain

Each step reaches users once the datafile is published and their application refreshes it.

Related#

• Flags, for the rollout basics
• Experiments, to compare variations instead
• Configuration rollback
• Testing in production