Why and How to Add Feature Toggles to Your Software

As a seasoned full-stack developer and software architect, I‘ve seen first-hand how feature toggles can revolutionize the way software is delivered. By allowing development teams to decouple deployments from releases, feature toggles enable more agile and less risky product delivery. In this in-depth guide, I‘ll share my experience with implementing feature toggles and best practices for using them effectively.

What are Feature Toggles?

Feature toggles (also known as feature flags, feature flippers, or feature switches) are a software development technique that allows teams to modify system behavior without changing code. They work by wrapping new functionality in conditional blocks that can be toggled on or off at runtime based on configuration.

Here‘s a simple example of a feature toggle in code:

if (featureIsEnabled("new-checkout")) {
    // new checkout logic
} else {
    // old checkout logic
}

By abstracting the control of features into configuration files or a feature management system, feature toggles separate deployment of code from release of features. This enables a number of powerful capabilities like canary releases, A/B testing, and permission-based access control.

Benefits of Feature Toggles

The 2021 State of Feature Delivery Report from LaunchDarkly found that elite software teams are 2-3 times more likely to be using feature flags than low-performing teams. Some of the key benefits driving this adoption include:

• Increased Release Velocity – Feature toggles allow teams to continuously deploy partially-complete features and avoid merge conflicts and long-running feature branches. The 2021 State of DevOps Report found that elite performers deploy 973x more frequently than low performers.

• Reduced Release Risk – With feature toggles, high-risk changes can be deployed to production but kept switched off until they are ready. If something goes wrong, the feature can be quickly toggled off without a hotfix deploy. Microsoft reported a 99% reduction in incidents after moving to feature flags.

• Progressive Delivery – Toggles enable canary releases and percentage rollouts to limit the blast radius of new changes. A 2019 report from Forrester found that using feature flags to ramp up and validate new features with a small user cohort before releasing to everyone can reduce the risk of production failures by up to 90%.

• Experimentation and Customization – Feature toggles are a key enabler for A/B testing and personalizing user experience. Teams at Bing reported a 10-25% increase in clicks and revenue by using feature flags to continuously experiment and roll out winning variations.

Feature Toggle Implementation Patterns

There are a few common patterns for implementing feature toggles in your codebase:

1. Release Toggles – These are short-lived toggles used to enable continuous delivery of partially-ready features. They are typically used at the entry point of a new code path and removed soon after release. Avoid scattering release toggles throughout the code.

2. Experiment Toggles – These toggles are used to perform A/B tests and multivariate experiments. They are usually managed in an experimentation platform and dynamically toggled at runtime for different user cohorts. Experiment toggles can hang around for a while but should have a defined expiration.

3. Ops Toggles – These toggles control operational aspects of the system such as performance optimizations, circuit breakers, or maintenance modes. They tend to be long-lived and should be carefully managed to avoid technical debt.

4. Permission Toggles – Also known as entitlement toggles, these are used to enforce access control and turn features on or off for certain users, groups, or license tiers. They are often used for premium features in SaaS applications.

In terms of where to put toggles in your code, there are a few options:

• Build-time Toggles – With this approach, the toggle is checked at build time and the unused code paths are excluded from the final binary. This is good for eliminating dead code but requires a redeploy to modify toggle state.

• Run-time Toggles – These toggles are checked dynamically at runtime, allowing the toggle state to be modified without a redeploy. Run-time toggles can be implemented as static (hardcoded in source) or dynamic (pulled from a remote configuration).

Here‘s an example of a static run-time toggle in Java:

public class PricingCalculator {
    public static boolean newPricingEnabled = false;

    public double calculatePrice() {
        if (newPricingEnabled) {
            // new pricing logic
        } else {
            // old pricing logic
        }
    }
}

And here‘s a dynamic run-time toggle using the Unleash Java client:

public class PricingCalculator {
    private final UnleashClient unleash;

    public PricingCalculator(UnleashClient unleash) {
        this.unleash = unleash;
    }

    public double calculatePrice() {
        if (unleash.isEnabled("new-pricing")) {
            // new pricing logic
        } else {
            // old pricing logic
        }
    }
}

Feature Toggle Management

For small-scale use cases, it‘s fine to manage feature toggles in a configuration file or database table. But as you scale to hundreds or thousands of toggles across multiple environments and applications, it becomes important to use a purpose-built feature management platform.

Some popular open source options include:

• Unleash – Extensible open-source feature toggle service with SDKs for all major languages. Supports gradual rollouts, user targeting, and experimentation.
• Flipper – Ruby library for managing feature toggles with support for percentage rollouts, actor targeting, and group targeting.
• GrowthBook – Open-source platform for feature flagging and A/B testing with a visual editor and SQL-based experiment analysis.

Commercial solutions offer additional enterprise features like SAML SSO, audit logging, and AI-powered insights. Notable vendors in this space include:

• LaunchDarkly
• Split.io
• CloudBees Feature Flags (formerly Rollout)
• Optimizely Rollouts

When evaluating feature management platforms, look for:

• Client SDKs for your tech stack
• Toggle management UI with search and tags
• RBAC and audit logging
• Integration with your deployment pipeline
• Support for progressive delivery and experimentation
• Scalability and high availability

Best Practices for Effective Feature Toggles

Through years of practicing continuous delivery with feature toggles, I‘ve learned some key best practices:

1. Use Short-Lived Toggles – The longer a toggle exists, the more technical debt it accrues. Aim to remove release toggles within days and experiment toggles within weeks.

2. Keep Toggle Logic Separate – Avoid polluting your core business logic with toggle checks. Centralize toggle logic in functions, decorators, or inversion-of-control containers.

3. Avoid Toggle Proliferation – Too many toggles make your code hard to reason about. Be judicious about introducing new toggles and proactively prune stale ones.

4. Test Both Toggle States – Make sure your test suite has coverage for the toggled-on and toggled-off code paths, even if the feature isn‘t released yet.

5. Monitor Toggle Performance – Track metrics like toggle change rate, toggle errors, and application performance with toggles on/off to catch problems early.

6. Document Your Toggles – Maintain a central inventory of all your feature toggles with metadata like owner, creation date, and expected lifetime. Review regularly to identify debt.

7. Integrate with Delivery Pipeline – Automatically validate toggle config, run toggle-specific tests, and verify SLOs as part of your CI/CD process.

8. version Your Toggle Config – Check your toggle configuration files into version control so you have a history of changes and can roll back if needed.

9. Leverage for Incident Response – Have playbooks for using feature toggles to quickly isolate problematic code or traffic-shape during incidents.

10. Educate Your Team – Make sure everyone understands the purpose and process for feature toggles. Bake toggle reviews into your team rituals.

By following these best practices and establishing a robust feature toggle architecture, you can realize the benefits of continuous delivery while minimizing the risks and costs.

The Future of Feature Delivery

Looking ahead, I believe the use of feature toggles will only accelerate as software teams seek to deliver more value to customers faster. Forrester predicts that "adaptive enterprises" practicing continuous delivery and experimentation will grow at 3x the rate of their industry.

As feature toggle adoption grows, I expect to see more standardization around best practices and architectural patterns. We‘re already seeing a trend towards consolidation in the feature management platform space, with LaunchDarkly‘s $200M Series D and Optimizely‘s $105M acquisition of Rollout.

I‘m excited to see how machine learning and AI will be applied to feature management, from identifying high-performing flag configurations to predicting the optimal rollout strategy for a given feature. The future of software delivery is bright, and feature toggles are sure to play a starring role.

Conclusion

Feature toggles are a critical tool for any software team looking to deliver value to customers faster and more safely. By decoupling deployments from releases, feature toggles enable continuous delivery, experimentation, and customization with less risk.

Implementing feature toggles requires careful planning and discipline to avoid technical debt, but the benefits are well worth the effort. By investing in a robust feature toggle architecture and following best practices, you can unlock a new level of agility and innovation in your software development process.

Whether you‘re just getting started with feature toggles or scaling your practice to the next level, I hope this guide has equipped you with the knowledge and resources you need to succeed. Now go forth and toggle!