Safely Rolling Out Features Using Feature Flags

#sdlc #programming

In this article we will walk through steps to rollout an upgrade as safely as possible.

What you will need

  • A feature controller
  • A configuration for the feature
  • Infrastructure to deploy canary releases (optional; if you like to play with fire without wearing gloves)

Safely Rolling Out Change

alt An overview of safely rolling out change

  1. Create a feature in feature controller for the new feature with default value set to disabled. Write code for the new feature but behind this new condition using the feature controller. The code is now present, but disabled.
  2. Release the new binary with the new code. At this stage, the code is present but behind a flag and currently disabled. A failure at this stage would require you to revert to the older binaries.
  3. Now update the configuration files, add the configuration for the feature but still keep it disabled. The feature should still be inactive and any failure at this stage would require you to revert to older configuration file.
  4. Update the configuration to enable the feature for few canary deployments. A failed rollout would require terminating the canaries.
  5. Update the remaining deployments and activate this feature. The chances of failure at this stage are minimal since the feature is already tested with canary users.
  6. Now alter the code such that the default value for the feature is enabled. This should not make any difference since anyway the configuration was enabled for this feature. A failed rollout at this stage would require you to move back to previous binary.
  7. Update the configuration files and remove references of the feature. The code is anyway not using this configuration as per step 6.
  8. Update all code and remove the conditional behaviour around this feature. A failed rollout would require you to revert to previous version of the binary.
  9. Remove the code from feature controller.

These nine steps might be an overkill for they ensure that code is released smoothly. These steps may span across weeks or months and parallelly for many features as well.

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