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Engineering
Feature Flags
Best Practices

Feature flag standard

2024-12-01

A comprehensive standard for managing feature flags, covering types, naming conventions, implementation techniques, and best practices.

Standard for managing feature flags, incorporating insights from various sources:

Introduction

Feature flags, also known as feature toggles, enable teams to deploy new features to production in a controlled manner. This standard outlines the best practices for implementing, managing, and retiring feature flags.

Types of feature flags

  • Release Flags: Gradually roll out new features to users.
    • Example: Releasing a new shopping checkout flow incrementally to 10% of users.
  • Experiment Flags: A/B testing different variations of a feature.
    • Example: Testing different feed algorithms to see which increases engagement.
  • Operational Flags: Manage system operations like feature throttling.
    • Example: Routing transactions through alternative payment gateways during downtime.
  • Permission Flags: Control access to features based on user roles or subscriptions.
    • Example: Granting access to premium features only to subscribed users.

Naming conventions

Use clear, descriptive names that indicate the purpose of the flag. Prefix flags with their type:

  • release_newCheckoutFlow
  • experiment_UIVariantA
  • operational_enableLogging
  • permission_premiumFeature

Implementation techniques

Conditional statements

Using if-else statements in the codebase:

package main

import "fmt"

func isFlagEnabled(flagName string) bool {
	// Logic to retrieve flag state
	return true
}

func main() {
	if isFlagEnabled("MY_FEATURE_FLAG") {
		fmt.Println("Feature enabled")
	} else {
		fmt.Println("Feature disabled")
	}
}

Configuration files

Storing feature flag configurations in external files (.env):

package main

import (
    "fmt"
    "os"
)

func isFlagEnabled(flagName string) bool {
    return os.Getenv(flagName) == "true"
}

func main() {
    if isFlagEnabled("MY_FEATURE_FLAG") {
        fmt.Println("Feature enabled")
    } else {
        fmt.Println("Feature disabled")
    }
}

Database flags

Storing feature flag states in a database table:

FlagNameIsEnabled
release_newCheckoutFlowtrue
experiment_UIVariantAfalse
operational_enableLoggingtrue
permission_premiumFeaturetrue

Feature flag platforms

Specialized services like:

SDKs and libraries

Best practices

  1. Management and Visibility: Use a centralized system for managing feature flags. Make status visible to support and analytics teams.

  2. Progressive Rollout: Roll out progressively: internal testing → small group → full rollout. Monitor key metrics at each stage. Use canary releases.

  3. Rollback Strategy: Plan for rollback scenarios. Implement quick revert without affecting user experience. Conduct regular drills.

  4. Documentation: Document flag usage, purpose, state, and impact. Communicate changes to all relevant teams.

  5. Performance: Avoid excessive feature flags. Cache flag states outside loops. Monitor performance impact.

  6. Security: Ensure flags don't expose PII. Implement least privilege access. Conduct regular audits.

  7. Avoiding Complexity: Avoid dependencies between flags. Implement clean feature switches over excessive code branching.

  8. Retiring Flags: Plan removal of obsolete flags to avoid technical debt. Schedule cleanup as part of the release cycle.

  9. Testing: Test flags in different environments. Validate behavior under various conditions. Use A/B testing to compare impact.

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