What Are the Best Practices for Managing Feature Flags in Software Development?

Introduction

Feature flags have become an essential tool in modern software development, offering the flexibility to toggle features on and off without deploying new code. This blog synthesizes insights from various expert sources to guide you on the best practices for managing feature flags.

Before diving into best practices, it's crucial to understand what feature flags are, and what a modern feature flags management service looks like.

Understanding of Modern Feature Flags Management Services

Feature Flags, initially simple configurations in software, have evolved into sophisticated systems integral to modern software development. These tools enable developers to activate or deactivate specific functionalities, supporting a variety of processes including continuous integration, A/B testing, and user entitlement management.

In a modern Feature Flags Management Service, the focus is on high availability and performance, crucial for handling diverse business scenarios. This system is deeply embedded in the software development lifecycle, emphasizing the importance of seamless integration with various ecosystems.

Key applications of Feature Flags include:

• Continuous Integration and Delivery: Facilitating separation of deployment from release, supporting trunk-based development.
• Risk Management in Feature Releases: Utilized for canary releases and progressive rollouts to minimize launch risks.
• Data-Driven Decision Making: Enabling A/B testing and experimental feature releases for informed development decisions.
• Entitlement Management: Managing user access, differentiating between free, paid, and enterprise users.

Feature Flags have become essential in modern software development, offering dynamic control over software features and playing a critical role in risk management, testing strategies, and user access governance.

Best Practices for Choosing/Designing Your Feature Flags Management Service

When choosing a feature flag tool or you design your feature flags management service by yourself, I recommend you to consider the following essential factors:

Centralized Feature Management System

Centralized feature management system is crucial for streamlined control and enhanced efficiency. Employing a unified dashboard that displays vital information such as flag ownership, current status, and change history is recommended. Incorporate features like Single Sign-On (SSO), permission controls, and change requests to ensure large teams can effectively collaborate on their projects and environments.

Design for Failure: Availability First

To ensure the feature flag management service is robust (high performance, high availability) and user-friendly (adaptable to a wide range of business scenarios), it should be designed with the following principles in mind:

• Built on Microservice Architecture to facilitate continuous improvement and delivery, component decoupling, and support for high availability and performance.
• Incorporation of various storage types to cater to different business needs. For instance, Redis for high-performance scenarios and ClickHouse for high-volume scenarios.
• Utilization of Edge Services, CDN, and Multiple Data Centers to ensure low latency and high availability.
• Focus on zero dependencies on real-time flag evaluations, graceful degradation, and robust SDKs with local caching.

Horizontal Scaling: Separation of Concerns

Effective architectural strategies are crucial for scalable feature flag systems. Decouple reading and writing of feature flags into separate APIs and Services to facilitate scaling, enhance caching, improve security, and simplify maintenance. Key strategies include decoupling of read/write APIs, enhanced caching, and simplified maintenance.

Performance Efficiency

Performance under load is crucial for feature flag tools, especially in high-traffic scenarios. Assess the tool’s performance through benchmarks, case studies, and user testimonials. To enhance user experience, I recommend also focus on server-side evaluation of feature flags, minimizing latency and enabling offline functionality, especially beneficial for mobile apps and services in remote areas.

Self-Hosted Open Source Solution

A self-hosted solutions gives you control over your data and infrastructure. Ensure the tool can be deployed on your own servers or private cloud and check for any dependencies or infrastructure requirements. Deployment using Kubernetes or Terraform to accommodate diverse deployment needs, simplifying service deployment and upgrades.

Integration with Data Analysis Tools: Data-Driven Insights

In today's software development environment, integrating feature flag tools with data analysis platforms is changing how we gain insights. This combination allows the transmission of feature usage data for deeper analysis. It enables detailed exploration of feature interactions and supports advanced A/B testing for multi-experiment scenarios, enhancing data-driven decision-making. This integration marks a significant step forward in understanding and leveraging software features effectively.

Integration with Observability: Minimizing Blast Radius

In the dynamic landscape of software development, the fusion of feature flag tools with Application Performance Management (APM) and Real User Monitoring (RUM) tools is increasingly vital. This integration is key in improving observability and reducing the impact of potential issues. Sending deployment events to APM tools provides developers with critical insights, aiding in the precise identification and assessment of the impact of incidents. Integrating trigger-based workflows further enhances this process, promoting immediate response capabilities. This streamlined integration facilitates more efficient incident management and strengthens the overall health of the application, leading to a more dependable and user-centric experience. Adopting this strategy marks a significant advance in proactive incident management and the maintenance of system reliability.

Active Maintenance

For feature flag open source solutions, regular updates and maintenance reflect the reliability and developer commitment of a feature flag tool. Check for recent commits, issue resolutions, and active community discussions in the tool's repository.

Technical Stack Alignment

Ensuring compatibility with your existing tech stack is vital for seamless integration. Confirm support for your programming languages and frameworks, and availability of SDKs or APIs. Important considerations are compatibility with programming languages, support for frameworks, and availability of SDKs or APIs.

Quality Documentation

Accessible and thorough documentation is key for effective tool utilization. Look for detailed guides, API documentation, FAQs, and case studies.

Robust Security

Security is a paramount concern, as feature flags directly impact application behavior and user data. Evaluate encryption, access control, and compliance with security standards.

Quality over Popularity

Quality assessment should be prioritized over popularity metrics in tool selection. Evaluate based on features, performance, community support, and alignment with your needs, rather than just popularity. Assess based on feature assessment, performance evaluation, and community support.

Best Practices for Implementing Feature Flags Cross Projects

Once you have chosen a feature flag tool, it's time to implement it in your projects. Here are some best practices for implementing feature flags cross projects:

Best Practices for Naming Feature Flags

Feature flags can be implemented to achieve various objectives:

• Release Flags: Enable the rollout of production code before a feature is publicly released.
• Experiment Flags: Facilitate A/B testing by controlling which group of users receives a specific experience.
• Permission Flags: Grant or restrict access to certain features for different customers.
• Kill Flags: Enable graceful degradation of your product in cases of performance issues or overload.
• Having clear naming conventions for each type of flag ensures that their purpose remains clear to everyone, even years later.

Avoiding Nested Feature Flags

Deeply nested code, similar to the example below, often suffers from high cyclomatic complexity, making it challenging to comprehend and manage:

if(FeatureA1Enabled) {
  if(FeatureB1Enabled) {
    ...
  } else {
    if(FeatureA2Enabled) {
      ...
    } else {
      ...
    }
  }
}

This complexity issue also applies to feature flags. Each feature flag check introduces a potential branch in your code, influencing its execution path based on the flag's state. Nested feature flags complicate the process of enabling or disabling features for specific user groups and increase the likelihood of mistakes, leading to unexpected outcomes. Therefore, avoid unnecessarily nesting them.

void Interdependencies Among Feature Flags

Each flag should serve a distinct, independent purpose. For permission flags, this means that the code must be modular enough to allow different features to be activated in any combination.

Requiring multiple flags to enable a specific use case, or having flags that potentially conflict with others, can lead to confusion in flag management. Such complexities in flag settings are likely to cause problems with user experiences sooner or later.

Utilizing Feature Flags to Minimize Code Branching

When a product team discusses the implementation of a substantial feature, it's crucial to consider the role of feature flags early in the process.

By implementing a feature flag and initially keeping it turned off, you can avoid creating long-lived feature branches. This approach allows the new feature's code to be continuously integrated and released without exposing it to users. This practice is particularly effective in CI/CD (Continuous Integration/Continuous Delivery) environments or during agile sprint deployments. It enhances the integrity of your codebase by avoiding complex merge processes and swiftly identifying any conflicts.

Additionally, this method effectively separates the code release process from the actual unveiling of new features to end-users.

Ensuring Accurate User Identification

The precision of user identification is crucial, especially when some tools evaluate flags based on a user's unique ID. The more accurately users are identified, the more effectively you can target your flags.

Maintaining a "sticky" ID is essential to ensure consistent flag evaluation for each user within your product. Inconsistent identification may lead to variable flag evaluations, as the user might be categorized into different variants each time.

For flags rolled out based on group analytics or individual user properties, accurate identification also involves proper setup of these parameters. Users need to be correctly assigned to groups or possess specific properties for your feature flag service to accurately evaluate flags dependent on these criteria.

Granting Feature Flag Access to Relevant Team Members

It's best practice to provide all team members who have a stake in the project with some level of permission to access, manage, and update the feature flag configurations. For instance, Instagram allows both their product managers and sales teams to control user access to specific features.

For ease of use, the hosted version of your feature flag system can be integrated with your existing user authentication system. The aim is to streamline and simplify the team's user management experience.

Organizing Feature Flags into Groups

Streamlining feature flag maintenance can be achieved by grouping them effectively. Different teams may have varied approaches to grouping their feature flags.

One method is to categorize feature flags into simple and high-level categories. Another approach is to organize them into broader categories such as release features, operational features, and experimental features.

Regularly reviewing and updating how you group your features should be an integral part of your workflow.

Implementing feature flag management practices need not be a daunting task. In fact, most of these practices are readily supported by popular feature flag management solutions. These practices can significantly enhance the efficiency of your software development team, allowing feature flags to effectively drive development.

Feature Flags: Designed for a Short Lifecycle

Our feature flag management approach underscores their temporary nature, distinguishing them from permanent application configurations. Feature flags are intended to be short-lived, modified dynamically at runtime, and retired after the rollout of new features. To manage them efficiently, we assign expiration dates, consider them akin to technical debt requiring periodic review and cleanup, and archive them when they're no longer necessary. This approach ensures code simplicity and avoids legacy complications. There are exceptions, such as kill-switches or debugging flags, but generally, limiting the duration of feature flags is essential for a streamlined and efficient application lifecycle.

Opt for SDKs Over REST APIs

When implementing feature flags in your code, it's advisable to avoid using REST APIs for retrieving these flags. This approach can slow down your application and introduce issues such as thread safety, network latency, and bootstrap inconsistency.

Unless there's a specific requirement for your application, using SDKs provided by third parties is a better choice. These SDKs cache feature flags in memory and update them using methods like long-polling, WebSockets, SSE, or gRPC. This approach is more efficient and reliable. Particularly for locally evaluated feature flags, there's no need to rewrite the evaluation logic in your application. Third-party SDKs are also regularly updated to stay compatible with the latest feature flag management services, often including a downgrade mechanism to ensure SDK compatibility.

Furthermore, I highly recommend using the OpenFeature standardized feature flags SDK to avoid vendor lock-in.

Opt for Local Evaluation to Speed Up

For back-end services, rich applications, and even mobile applications, evaluating your feature flags locally can enhance the overall system performance.

By doing so, your evaluation server faces less workload, allowing it to concentrate on processing requests from devices with limited computing capabilities. Your application benefits from reduced network latency, as it can quickly retrieve evaluation results from a local cache. However, I advise against using local evaluation for lightweight applications, such as web applications. These may contain hundreds of feature flags, and the evaluation logic can be complex and memory-intensive.

Quick Access through Flag Bootstrapping

Bootstrapping feature flags ensures they are immediately available in the client, essential for scenarios like A/B testing on landing pages or redirect tests. Without bootstrapping, there's a delay waiting for the library to load and request the flag data, causing the page to load without the necessary flag information.

Implementing bootstrapping also guarantees accurate feature flag data for event tracking. You can achieve this by adding a bootstrap configuration with your required feature flags to your application. This setup allows the flags to be initialized as soon as the application loads, or you can alternatively assign default values to each flag for immediate use.

Assessing Feature Flag Appropriateness

When adopting feature flags, development teams must evaluate their suitability for upcoming tasks. Feature flags, while useful, can increase decision points in code and add technical debt. It's crucial for teams to have an effective feature-flag strategy to minimize the number of flags in the code and manage technical debt more cautiously.

We recommend integrating feature flag patterns into the planning process of new features. For larger teams, this includes involving both the product manager and the software development team in discussions. Incorporating feature flags in release strategy talks with the product team adds a layer of transparency, aiding the development team in understanding the feature's business relevance.

Streamline with Single-Use Feature Flags

For clarity and simplicity, use one feature flag per component, function, or class. Multiple uses of the same flag can lead to maintenance challenges and potential errors. Keeping feature flags focused and limited ensures easier management and understanding.

Regularly Clean Up Feature Flags

Feature flags, while useful, can clutter your codebase and make it less readable. Once a feature is fully rolled out to all users, it's best to remove its feature flag from the codebase. At this point, the feature is always enabled, eliminating the need for conditional checks.

Leaving feature flag code in the codebase poses risks, such as accidental deactivation of the feature for some or all users. However, consider retaining certain flags as kill switches for quickly disabling features in case of issues.

When deciding whether to keep a feature flag, balance the convenience of a kill switch against the burden of maintaining additional code.

Conclusion

In conclusion, effective management of feature flags in software development involves clear naming conventions, avoiding nested flags, ensuring independent flag functionality, and integrating feature flags early in the development process. Employing SDKs for efficient flag retrieval, local evaluation for performance, and regular flag cleanup maintains code clarity. Balancing these practices with the needs of your team and project will streamline development, enhance user experience, and ensure the successful implementation and management of feature flags.