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Feature Flags Library and Flow

Timeline​

TimeDescription
2022-11-15 09:00:00Initial file creation

Status: Accepted​

Context​

In the current form of the software we don't have the possibility to provide a new feature to a selected group of users or hide the feature from the users completely without releasing a new version of the product. This state is problematic from various platform parts perspective:

  • OneBox Chrome Extension depends on Google Chrome Web Store review process for releases, which means that the release of new features may be delayed.
  • We want to release more often, but we don't want all the new features to be accessible by our users right away.

Decision​

The decision is to implement feature toggles functionality in all the user facing parts of our product which includes:

  • OneBox Chrome extension
  • VS Code extension
  • Web application
  • Backend

In addition to the above the feature flags state needs to be read dynamically by the mentioned applications, which means that the feature toggles should be written into a persistence store or a file and served dynamically depending on the user.

Some of the potential solutions that are actively developed include using a dedicated library such as:

  • unleash - open source feature management solution with dashboard allowing to control the active feature flags.
  • LaunchDarkly - a commercial platform for feature toggles allowing for fine grained control and dashboards.
  • GO Feature Flag - an open source supporting feature toggles that we would have to build the frontend part on.

I suggest going with unleash, because of:

  • actively developed
  • natively written in Golang
  • persistence on top of PostgreSQL
  • available as Docker container
  • experimental Svelte SDK available

The Final Decision​

We are going with unleash.

Consequences​

The introduction of the feature flags and their implementation in every part of the product will make it easier to release the software with features hidden from the users and will allow dynamic control over the features just by releasing backend. That means:

  • OneBox Chrome Extension - with feature flags added to the product we will have the possibility of releasing the software with features that are hidden and will be gradually introduced to new users once tested and verified.
  • We will be able to release more often, without delivering the features right away to the users. Using feature flags we can easily limit the target audience of the new features and change the audience dynamically.
  • Ability to do feature based A/B testing based on users or user groups.
  • Ability to turn off a faulty feature that is broken and requires substantial effort to fix and deliver to users.