links:: feature toggles MOC

Feature Toggles Slides

Agenda

• Introduction
• How feature flags work
• Benefits of feature flags
• Categories of toggles
• Implementation techniques
• Toggle configuration
• Best Practices for using feature flags
• Testing feature toggles
• Potential drawbacks of feature flags
• Conclusion

Definition

safer and more frequent deployments

facilitate testing

gathering feedback on new features

release new features to a small group of users

test different variations of a feature

manage technical debt

easier to maintain and update an application over time

Why Feature Toggles?

Conditional statement

if ( featureFlagEnabled) {

  // execute code for feature

} else {

  // execute default code

}

How Feature Flags Work

Toggle configuration control

Source: https://martinfowler.com

• Canary releases / Product testing
• Dark launching
• Blue-green deployments
• Migrations
• System outage

Benefits of Feature Flags

Source: https://www.atlassian.com/continuous-delivery/principles/feature-flags

• Safer and more frequent deployments
• Controlled rollout of new features
• Testing and gathering feedback

Categories of Toggles

• Release Toggles
• Experiment Toggles
• Ops Toggles
• Permissioning Toggles

Source: https://martinfowler.com

… enable trunk-based development for teams practicing Continuous Delivery. They allow in-progress features to be checked into a shared integration branch (e.g. master or trunk) while still allowing that branch to be deployed to production at any time.

Release Toggles allow incomplete and un-tested codepaths to be shipped to production as latent code which may never be turned on.

Source: https://martinfowler.com

Release toggles

• No longer than a week or two
• Typically very static

Source: https://martinfowler.com

Implementation Techniques

• De-coupling decision points from decision logic
• Inversion of Decision
• Avoiding conditionals

Source: https://martinfowler.com

Toggle Configuration

Source control and re-deployments

Hardcoded Toggle Configuration

Parameterized Toggle Configuration (via command-line arguments or environment variables)

Toggle Configuration File

• Dynamic configuration
• Distributed toggle configuration
• Configuration services (Harness)
• Azure App Configuration

Tools: Azure App Configuration

Source: https://learn.microsoft.com/en-us/azure/azure-app-configuration/

Azure App Configuration provides a service to centrally manage application settings and feature flags.

Enables staged rollout of features for targeted audiences

The feature flag is always enabled for user test@contoso.com, because test@contoso.com is listed in the Users section.

The feature flag is enabled for 50% of other users in the contoso.com group, because contoso.com is listed in the Groups section with a Percentage of 50.

The feature is always disabled for all other users, because the Default percentage is set to 0.

Best Practices for Using Feature Flags

• Clear naming conventions
• Regular maintenance and cleanup
• Monitoring and logging

Testing Feature Toggles

Testing without feature toggles

Exploratory testing

Test E1
Test E2
…
Test En

Regression testing

Test R1
Test R2
…
Test Rn

Testing with feature toggles

Number of toggles N=2

Number of combinations C=4

Test each combination?

Test E1 – It is safe to skip it 
Test E2 – It is hard do decide. Is it safe to skip it?
Test E3 – We should test this.
...
Test En

Exploratory testing

Regression testing

Test R1 - It is safe to skip it 
Test R2 - It is hard do decide. Is it safe to skip it?
Test R3 – We should test this. 
…
Test Rn

Testing with feature toggles

• Number of toggles N=16
• Number of combinations C=65,536

Integration, E2E testing of large number of flags

Source: https://launchdarkly.com/blog/testing-with-feature-flags/

How do we test this?

• Option 1:

  • Test all combinations. Good luck :)

  • Minimal risk of missing bugs.

• Option 2:

  • Assess all combinations and select only “realistic” ones which are likely to occur in the future. Test them.
  • Accept the risk of “unknown”.
  • This will most likely require a lot of time and effort.

• Option 3:

  • Follow recommendation from the book. Use the current production configuration plus: 3 combinations (see next slide).
  • Accept the risk of “unknown”.
  • This will require less time and effort compared to option 1

Static, Boolean and release toggles

Use the current production configuration plus:

1. Any toggles you intend to release set to ON
2. Any toggles you intend to release set to OFF
3. All toggles set to ON

Source: https://martinfowler.com

Testing of large number of flags (option 3)

Other strategies

1. Dynamic toggle: test users who move into or out of the targeted group
2. Experiment toggle: test consistency across user sessions, to ensure individual users are given the correct version at every login.
3. Permission toggle: explore toggle combinations to see how the new configuration interacts with existing option

Potential Drawbacks of Feature Flags

• Increased complexity and technical debt
• Risk of feature flag fatigue
• Overreliance on feature flags

Conclusion

• Feature flags are a powerful tool
• Follow best practices
• Testing will likely require more time and effort and understanding of context
• Will have to accept risks of “unknown” (not tested combinations)

References

• https://martinfowler.com/articles/feature-toggles.htm
• https://martinfowler.com/bliki/CanaryRelease.html
• http://swreflections.blogspot.com/2014/08/feature-toggles-are-one-of-worst-kinds.html
• https://www.abhishek-tiwari.com/decoupling-deployment-and-release-feature-toggles/https://launchdarkly.com/blog/testing-with-feature-flags/
• https://dougseven.com/2014/04/17/knightmare-a-devops-cautionary-tale/
• https://learn.microsoft.com/en-us/azure/azure-app-configuration/
• https://www.atlassian.com/continuous-delivery/principles/feature-flags