Feature Flags in Spring Boot

In the ever-evolving landscape of software development, agility is key. Delivering new features rapidly while maintaining a stable production environment is a critical capability for any development team. Feature flags offer a powerful tool to achieve this balance, allowing developers to turn features on or off without redeployment. In this article, we’ll explore how to implement feature flags in a Spring Boot application, and how they can support agile practices like continuous integration and A/B testing.

What are Feature?Flags?

Feature flags, also known as feature toggles, are a technique in software development that allows specific features of an application to be conditionally enabled or disabled at runtime. This means you can release code to production without exposing new features until they are fully tested and ready for prime time.

By using feature flags, developers can integrate their changes frequently, even if a feature isn’t fully complete, ensuring the main branch remains stable and deployable. This approach is particularly valuable in trunk-based development, where long-lived branches are avoided to reduce merge conflicts and integration issues.

Implementing Feature Flags in Spring?Boot

Spring Boot provides several ways to implement feature flags, ranging from simple configurations to more sophisticated setups. Let’s walk through some common approaches.

1. Using Spring?Profiles

Spring profiles are a built-in feature of Spring Boot that allows you to define different beans for different environments. This can be an effective way to manage feature flags at the application level.

For example, suppose you’re developing a new Bitcoin mining algorithm that you want to test in a non-production environment:

@Configuration
public class MiningConfig {

    @Bean
    @Profile("default")
    public BitcoinMiner defaultMiner() {
        return new DefaultBitcoinMiner();
    }

    @Bean
    @Profile("experimental")
    public BitcoinMiner experimentalMiner() {
        return new ExperimentalBitcoinMiner();
    }
}        

In this setup, the default profile uses the existing algorithm, while the experimental profile activates the new one. By simply switching profiles, you can control which version of the feature is active without changing any code.

2. Using Conditional Properties

Another approach is to use Spring Boot’s @ConditionalOnProperty annotation, which allows you to toggle features based on configuration properties

@Configuration
public class FeatureFlagConfig {

    @Bean
    @ConditionalOnProperty(name = "features.experimental-miner", havingValue = "true")
    public BitcoinMiner experimentalMiner() {
        return new ExperimentalBitcoinMiner();
    }

    @Bean
    @ConditionalOnProperty(name = "features.experimental-miner", havingValue = "false", matchIfMissing = true)
    public BitcoinMiner defaultMiner() {
        return new DefaultBitcoinMiner();
    }
}        

Here, the feature flag is controlled by a property in your application.yml file:

features:
  experimental-miner: true        

This approach provides more granularity and flexibility, allowing you to enable or disable features dynamically across different environments.

Advanced Feature Flagging with?Togglz

For more complex scenarios, such as A/B testing or canary releases, you might need a more robust solution. This is where Togglz comes in. Togglz is a feature flag library that integrates seamlessly with Spring Boot and provides advanced features like gradual rollouts, user targeting, and even scripting capabilities.

1. Setup and Configuration

To get started with Togglz, add the following dependency to your pom.xml:

<dependency>
    <groupId>org.togglz</groupId>
    <artifactId>togglz-spring-boot-starter</artifactId>
    <version>2.9.0</version>
</dependency>        

Next, define your feature flags as an enum:

public enum FeatureFlags implements Feature {

    @Label("Experimental Miner")
    EXPERIMENTAL_MINER,

    @Label("New UI")
    NEW_UI;

    public boolean isActive() {
        return FeatureContext.getFeatureManager().isActive(this);
    }
}        

With Togglz, you can activate these flags based on various conditions, such as user roles, server IPs, or even custom scripts.

2. Using Togglz in Your Application

You can now use these feature flags in your application code:

if (FeatureFlags.EXPERIMENTAL_MINER.isActive()) {
    // Use the experimental miner
} else {
    // Use the default miner
}        

This setup allows you to roll out features gradually, test them with a subset of users, and gather feedback before a full release.

Use Cases for Feature?Flags

Feature flags can be applied in a variety of scenarios to improve your development workflow:

1. Trunk-Based Development: Integrate frequently and hide incomplete features behind flags to keep the main branch always deployable.
2. A/B Testing: Show different versions of a feature to different users and analyze which version performs better.
3. Canary Releases: Gradually roll out new features to a small group of users and monitor their behavior before a full release.
4. Environment-Specific Configuration: Enable or disable features based on the environment, such as using different security settings for development and production.

Conclusion

Feature flags are a versatile tool in the developer’s toolkit, enabling more flexible and agile development practices. Whether you’re using Spring Boot’s built-in capabilities or integrating with a more advanced tool like Togglz, feature flags can help you deliver features faster, with less risk, and more confidence.

If you haven’t explored feature flags in your Spring Boot projects yet, now might be the perfect time to start. They can be the key to unlocking a more streamlined and resilient CI/CD pipeline.