Feature Flag

A minor implementation of Fowler's feature toggle designed for enabling and dialing up a feature for a percentage of traffic in a consistent way. Provides for the following:

• Shared configuration for feature flags across multiple services (etcd, jdbc, etc)
• Quick disablement of a feature
• Ability to dial up a percentage of traffic based on a common identifier.
• Dial up is consistent. (At x% dial up, the same identifier will consistent be enabled or disabled)

Repository Status

Installation

All libraries are available on maven central.

Library	Purpose	Version
feature-flag	Core Library
feature-flag-ddb	DynamoDB backend
feature-flag-sql	SQL backend
feature-flag-etcd	etcd backend
feature-flag-metrics	metrics integration

Sample Code

DynamoDB usage example

  void setupDynamoDB(Metrics metrics, DynamoDbClient dbClient) {
    MetricsDecorator metricsDecorator = new MetricsDecorator(metrics);
    DynamoDbConfiguration dbConfiguration = ImmutableDynamoDbConfiguration.builder().build();
    featureManager = new FeatureManager.Builder()
        .withFeatureManagerDecorator(metricsDecorator.featureManagerDecorator())
        .withFeatureLookupManagerDecorator(metricsDecorator.featureLookupManagerDecorator())
        .withFeatureLookupManager(new DdbFeatureLookupManager(dbConfiguration, dbClient))
        .build();
  }

  String calculateResult(String customerId) {
    if (featureManager.isEnabled("updatedCalculation", customerId)) {
      return existingProcess(customerId);
    } else {
      return newProcess(customerId);
    }
  }

  String calculateResultCallables(String customerId) {
    return featureManager.ifEnabledElse("updatedCalculation", customerId,
        () -> existingProcess(customerId),
        () -> newProcess(customerId));
  }

Notes

• SQL support just started, should work but not completely tested.
• Metrics here use the base metrics library from CodeHead. I may optimize them more.
• The use of the builder is now required. FeatureManager.Builder class should be used.

Why not use an existing library?

• Current libraries are overly complicated or spring-based. (ff4j)
• Too many bells ans whistles and leaky abstractions.

Java Version Notice

These libraries require Java 21.

TODO

1. Generic CLI would be nice.