Trunk based development

Merge unfinished work into main every day, behind a flag that stays off wherever users are. Branches stay short, and the work is released when it is ready rather than when it is merged.

Hide the unfinished code#

Start from the example with staging and production environments, and keep the new checkout on in staging and off in production:

npx @featurevisor/cli@latest init --example=with-environments

description: Checkout redesign
bucketBy: userId
rules:
  staging:
    - key: everyone
      conditions: '*'
      percentage: 100
  production:
    - key: everyone
      conditions: '*'
      percentage: 0

Every change to the new checkout merges behind the flag, while the current checkout keeps working:

const context = {
  userId: user.id,
}
if (f.isEnabled('checkout', context)) {
  // the new checkout, still being built
} else {
  // the current checkout
}

Turn it on while you work#

To see the new checkout locally without touching the definition, give your development build a sticky value:

const f = createFeaturevisor({
  datafile,
  stickyFeatures: {
    checkout: { enabled: true },
  },
})

Sticky values win over the datafile, and stay out of what you commit to the Featurevisor project.

Test both paths#

Until the flag is gone, both code paths ship. Test each in your application's tests, with checkout sticky on and off. In the Featurevisor project, a test spec pins what each environment gets, so nobody turns it on in production by accident:

feature: checkout
assertions:
  - description: On in staging
    environment: staging
    at: 90
    expectedToBeEnabled: true
  - description: Off in production
    environment: production
    at: 10
    expectedToBeEnabled: false

What a flag cannot hide#

A flag only decides which code path runs. It cannot hide:

• database migrations, which run whatever the flag says
• side effects outside the code it guards, such as jobs and emails
• changes to an API that other services call

Make those changes so the current code keeps working with them, before the flag turns on anywhere.

Release and remove#

When the new checkout is complete, release it as Decoupled releases describes. Once it is at 100% everywhere, delete the old code path, then deprecate and archive the flag, so it does not linger. With code generation, regenerating after archiving turns any use you missed into a compile error.

Related#

• Decoupled releases
• Testing before deployment
• Deprecating features