🏁Feature toggles ("feature flags")

Go from static configs to dynamic configurations and spend less time deploying.

The code part of this book uses a handcrafted, simple feature flags engine and a small toggle configuration.

While a technically trivial solution, this enables a dynamic configuration that can be detached from the source code itself. In effect, this means we are one big step closer to separating a (technical) deployment from a (business-oriented) release.

The feature function is located at src/FeatureToggles. For the configuration part, we should put it on Mockachino so that we can approximate a more conventional feature toggles service, getting (and updating) flags without having to re-deploy our code. The set of feature toggles is ordered under each respective user group.

Unknown (or missing, non-existing, null...) users get the standard user group access.

Note that different feature toggle services or implementations may differ in how they exactly apply toggles, and how they work. In our case here, we apply group-level toggles rather than request individual flags, if nothing else than for simplicity of demonstration.

🎯 Example: The full configuration you can use as your template looks like the one below. Notice how it's segmented on the group level:

src/FeatureToggles/config/mock.toggles.json

{
  "error": {
    "enableBetaFeatures": false,
    "userGroup": "error"
  },
  "legacy": {
    "enableBetaFeatures": false,
    "userGroup": "legacy"
  },
  "beta": {
    "enableBetaFeatures": true,
    "userGroup": "beta"
  },
  "standard": {
    "enableBetaFeatures": false,
    "userGroup": "standard"
  },
  "dev": {
    "enableBetaFeatures": true,
    "userGroup": "dev"
  },
  "devNewFeature": {
    "enableBetaFeatures": true,
    "enableNewUserApi": true,
    "userGroup": "devNewFeature"
  },
  "qa": {
    "enableBetaFeatures": false,
    "userGroup": "qa"
  }
}

You can update the flags as you want, to get the effects you need, without requiring redeploying the code!

Refer to FeatureFlags.io and to Unleash's documentation on activation strategies for inspiration.