Feature flags: deliver and test new features in production

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This article covers the fundamentals of feature flags, key factors to consider when choosing a feature flag provider, use cases to illustrate their effectiveness, and valuable lessons learned along with best practices accumulated over some years of experience.

When it comes to delivering new features in software development, the traditional approach often involves a complete development and quality assurance process. This typically requires significant time and effort before the features are deemed ready for production. However, an alternative method exists that offers greater efficiency and flexibility: the use of feature flags.

Feature flags are a technique used to enable or disable specific features within an application. Instead of going through the entire development cycle for a new feature, developers can implement it behind a feature flag. This means that the new functionality is embedded within the codebase but remains hidden and inaccessible to end users. By selectively enabling the feature flag, developers can control which users have access to the new feature.

Implementing feature flags allows for incremental development and testing of new functionalities. It enables the team to release features to a limited set of users, such as internal stakeholders or a subset of customers, before rolling them out to the entire user base.

Feature Flags Advantages

Controlled Rollouts

Feature flags allow for controlled rollouts of new features. By gradually enabling the feature for a small group of users, developers can gather feedback, monitor performance, and address any issues or bugs that may arise. This iterative process ensures a smoother and more reliable release.

Continuous Integration

Feature flags facilitate continuous integration and continuous deployment practices. Instead of deploying large updates or waiting for specific release cycles, new features can be added to the codebase incrementally and continuously. This promotes faster development cycles and more frequent releases.

Risk Mitigation

By using feature flags, the impact of new features on the existing codebase and user experience can be mitigated. If an issue or bug is identified after enabling a feature flag, it can be quickly disabled without requiring a full rollback of the entire application. This reduces the risk associated with introducing new functionalities.

While feature flags can be managed internally, it is worth noting that numerous feature flag providers specialize in scalable solutions tailored to meet specific project requirements. These providers offer support for various programming languages and environments, including serverless architectures and monolithic systems. Thus, regardless of the context of your code, feature flag providers present versatile options to streamline the integration of new functionalities.

In the following section, some considerations regarding selecting a feature flag provider are presented.

Considerations for selecting a feature flag provider

Client-side SDKs

Ensure that the feature flag provider offers a client-side SDK that is compatible with your project. This SDK allows seamless integration of feature flags into your client-side code.

Server-side SDKs

Similarly, verify if the feature flag provider offers server-side SDKs. These SDKs enable validation of flags received from clients and facilitate backend functionality segregation.

Targeting Capabilities

Evaluate the feature flag provider's targeting mechanisms. Targeting allows you to categorize and manage users based on specific criteria, ensuring precise control over which users receive certain flags.

Approval Workflows

Depending on the size of your team and project requirements, consider if the feature flag provider supports approval workflows. This feature enables the implementation of a review and approval process for feature flags before they go live.


Take into account the pricing structure of the feature flag provider. Consider factors such as the number of flags, users, and additional features offered. Ensure that the provider's pricing aligns with your project's budget and requirements.

Integration Hooks

Check if the feature flag provider offers integration hooks or extensibility options. Hooks allow you to customize and extend the functionality of the feature flag system to better fit your project's needs.

Failover Mechanisms

Assess whether the feature flag provider includes failover mechanisms. Failovers ensure that the feature flag system remains operational even in the event of unexpected failures or downtime.

Proxy Support

Determine if the feature flag provider supports proxy configurations. Proxy support can be beneficial in certain network setups, enabling smooth communication between the application and the feature flag provider's services.

Below you can find some providers of feature flags:

Different use cases for feature flags

Feature flags offer versatile applications across various use cases. Here are a few examples:

Adding new UI components

Feature flags are handy when you want to enhance your application's appearance by introducing new user interface (UI) components or functionalities. For example, you can easily incorporate a new button that utilizes existing functionality behind a feature flag.

Testing new functionality

Feature flags are ideal for safely testing and experimenting with new features. By selectively enabling the feature flag, you can gradually introduce and gather user feedback on the new functionality before making it available to all users.

Deprecating functionality

When you need to remove or replace a certain feature, feature flags can be used to deprecate functionality gradually. By employing feature flags, you can phase out the old functionality while introducing the new one, ensuring a smoother transition for your users.

Implementing a maintenance mode

Maintenance mode is one of the most valuable use cases for feature flags. In critical situations such as data breaches or leaks, having a maintenance mode feature flag in your code allows you to easily activate it. When enabled, this flag displays a maintenance page on the client side and disables all server endpoints, effectively communicating that the application is undergoing maintenance.

Enabling debugging mode

Feature flags can be utilized to activate debugging mode in your application. This is particularly useful during the development and troubleshooting phases, as it allows developers to enable additional logging, diagnostic tools, or specific debugging functionalities to identify and resolve issues more effectively.

Lessons learned and best practices for feature flags

Based on years of experience in continuous integration environments, the following are key lessons learned and best practices for effectively utilizing feature flags:

Consider potential failures

It is essential to anticipate the possibility of failures with your feature flag provider. Like any service, feature flag providers can experience downtime or issues. To mitigate the impact on your application, consider implementing a backup option or adding your own layer of feature flag management. Some providers offer proxy functionality, which can serve as a backup in case of provider failure.

Consistent flag naming

When implementing feature flags, it is crucial to establish a consistent naming convention. Choose a naming structure that aligns with your project's needs and stick to it. Consider adding suffixes or prefixes to distinguish different types of flags or their associated functionalities.

Set default values for flags

Always define a default value for your feature flags. This ensures that the application behaves as expected even if a flag is not explicitly enabled or if there are any issues with the flag configuration. Setting a default value provides a fallback option and helps maintain the integrity of your codebase.

Limited lifespan of flags

Feature flags should have a defined life cycle. Once a flag has been rolled out to all users and is no longer needed, it should be archived and removed from the codebase. This practice ensures that your codebase remains clean and avoids unnecessary clutter from deprecated flags.

Utilize monitoring tools

Take advantage of monitoring tools to track user interactions based on activated feature flags. Services like DataDog can provide valuable insights into user behavior and help you analyze the impact of specific feature flags. Monitoring user interactions allows for data-driven decision-making and aids in understanding the effectiveness of your feature flag implementation.

Wrapping Up

In conclusion, this article has explored the ins and outs of feature flags, including their fundamental concepts, the factors to consider when choosing a feature flag provider, various use cases, and valuable lessons learned. Feature flags have emerged as a robust tool, enabling organizations to handle customer features securely, facilitate continuous integration, and maintain control in case of errors or deployment failures. With the ability to leverage feature flags, businesses can ensure a smooth and regulated software release process, all while safeguarding the user experience. By embracing this powerful technique, organizations can confidently navigate the complexities of software development and deliver exceptional products to their users.

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