What is a feature flag?
A feature flag, also known as a feature toggle, is a software development tool that allows developers to turn features on or off in an application without deploying new code. Feature flags let teams separate deployments from feature releases, making it easier to practice Continuous Delivery. They also provide a way to test a feature in production with an easy rollback plan.
Feature flags help with stability by providing a controlled mechanism for activating features. You can activate a feature for a small group of customers to collect performance data and user feedback without impacting service reliability. If you have an ongoing incident, you could temporarily deactivate resource-intensive features to reduce system load. This minimizes risk and facilitates rapid testing and iteration.
Benefits of using feature flags
Feature flags benefit software development, deployments, and operations. Decoupling feature releases from code deployment means you can deploy small batches of work regularly instead of saving all the work involved in creating a feature for a single high-risk deployment.
- Controlled feature rollouts: Feature flags let you gradually deploy new features, reducing the risk of hitting all users with bugs or performance issues.
- Rapid iteration and experimentation: You can use feature flags to conduct A/B testing, provide early access to a subset of users, and collect real-world performance data to inform your decisions.
- Quick rollbacks: If you detect a functional or performance issue, you can quickly and safely deactivate a feature without rolling back or redeploying a previous software version.
- Improved deployment flexibility: You can deploy software versions that contain code for features that aren’t yet ready for use. Feature flags keep these features hidden until you’re ready to activate them.
- Simplified collaboration: Feature flags make it easier to integrate your code continuously into the main branch, as in-flight features can be switched off. When combined with frequent automated deployments, this reduces merge conflicts and deployment risk.
- Enhanced user segmentation: Feature flags let you tailor experiences for specific user groups, supporting personalization or targeted rollouts.
- Operational resilience: Operational flags let you adjust system behavior dynamically, enhancing response times during traffic spikes or system failures by switching off resource-intensive features.
Types of feature flags
1. Release toggles
Release toggles are temporary feature flags used to manage the gradual rollout of new features. They control which features are visible to end-users as they progress through development stages. Release toggles are critical for progressive delivery, allowing features to be tested and validated in production environments before a wider release.
These toggles help mitigate risks by allowing you to switch off a feature quickly if issues arise. They support Continuous Delivery practices, enabling features to be included in the main codebase before they are ready for release.
2. Experiment toggles
Experiment toggles facilitate A/B testing and experimentation by enabling developers to toggle features for different user groups. These toggles let you gather quantitative and qualitative data to assess feature performance and user engagement. By toggling features for specific segments, teams can measure impact and make data-driven decisions on feature enhancements.
These toggles support iterative product development, letting you test hypotheses in real-time with real users. The feedback you gather drives a user-centric approach that increases the chance new features will be useful.
3. Ops toggles
Ops toggles let you control operational features that change system behavior without directly impacting end users. You can use these to manage features like load balancing, circuit breakers, or logging levels. You can use ops toggles to react to system demand or as part of incident management.
Using ops toggles effectively makes your software more resilient as you can quickly switch off resource-intensive features when the system is under heavy load. Instead of risking a deployment to alleviate system load during an incident, you can quickly and safely release pressure by flipping an ops toggle.
4. Permission toggles
Permission toggles control feature access based on roles, licenses, or other criteria. They let you dynamically adjust feature access to support personalization, compliance, or other limitations on the feature. Permission toggles are usually based on specific users or groups.
By implementing permission toggles, organizations can protect sensitive data and maintain compliance with regulatory requirements. They offer a way to adapt the user interface experience based on user roles, ensuring that users have access only to features relevant to their needs.
How feature flags work
Here are some important technical aspects to be aware of when working with feature flags:
Decoupling deployment from release
Feature flags separate the concepts of deployment and release. Developers can deploy code frequently with in-flight features switched off, so the deployment cadence isn’t set by feature completion. Similarly, feature flags make it possible to release a feature without a deployment, as the flag can be updated to make a feature available.
This decoupling of concepts is beneficial as deployments and rollbacks are harder than switching a flag on or off. It also benefits concurrent feature development as developers can work on a feature without creating long-lived branches and without complex merge conflicts.
Dynamic versus static configuration
Feature flags can be dynamic or static. Static flags are changed in code or configuration files, so require a deployment to switch features on or off. Dynamic flags allow changes to be made at runtime without a deployment.
Static flags help keep in-flight features hidden from users but don’t decouple deployment and release. Dynamic configuration separates deployments and releases, enabling real-time experiments, getting early user feedback, and iterating to better features.
Implementing feature flags in code
To implement feature flags in code, you need to add conditional statements, attributes, or decorators that check the state of the flag for the given context. Though you could write a feature flag implementation, using a flag management system that implements OpenFeature is usually preferable.
As code will check feature flags frequently, you must ensure they have a minimal performance cost. You must also design feature flags to minimize code complexity, as checking flags with procedural if-statements can result in many logical branches. High-quality documentation and automated flag logic tests are crucial, as is deprecating and removing flags that are no longer useful.