Feature Flagging: using LaunchDarkly or open‑source alternatives

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Introduction

Shipping new features can be risky, especially when they affect critical user flows. Feature flagging helps you release safely by turning features on or off without redeploying your application. As a result, teams gain more control over rollouts, testing, and experimentation. In this post, we’ll explore how feature flagging works, when to use it, and how tools like LaunchDarkly or open-source alternatives can support a smooth, controlled release process.

What Is Feature Flagging?

A feature flag is a conditional switch in your code that decides whether a feature should be active. Instead of shipping everything at once, you wrap new features in flags and toggle them when ready. This enables gradual rollouts, A/B testing, and safe experimentation without code changes. Furthermore, if something goes wrong, you can disable the feature instantly.

Common Use Cases

  • Rolling out features gradually
  • Testing new functionality with small user groups
  • Running A/B or multivariate experiments
  • Enabling or disabling features for premium tiers
  • Safely deploying incomplete work
  • Instantly turning off problematic features

LaunchDarkly: A Fully Managed Feature Flag Platform

LaunchDarkly is one of the most popular platforms for feature flag management. It provides real-time toggles, user targeting, experimentation, and analytics — all accessible through a clean dashboard.

Key Features

  • Real-time flag updates without redeployment
  • User-based targeting and segmentation
  • Multivariate testing
  • Built-in experimentation and metrics
  • Audit logs for compliance
  • SDKs for almost every language

Why Use LaunchDarkly

LaunchDarkly excels at scale. It’s reliable, easy to integrate, and ideal for teams that need enterprise-level control. Its strongest advantage is instant propagation — feature updates reach users within seconds. Additionally, the dashboard makes it simple for non-engineers to enable or disable features safely.

Downsides

  • Higher cost compared to open-source solutions
  • Requires a cloud subscription
  • Overkill for small teams or hobby projects

Open-Source Alternatives to LaunchDarkly

Several open-source tools offer powerful feature flagging without subscription fees. Although they may require more setup and maintenance, they are excellent for teams wanting control and flexibility.

1. Unleash

Unleash is one of the most popular open-source feature flag platforms.
Highlights:

  • Self-hosted or cloud version
  • Role-based access control
  • Advanced targeting rules
  • SDKs for all major languages
    Unleash is a great choice if you want LaunchDarkly-level features without vendor lock-in.

2. Flagsmith

Flagsmith offers both cloud-hosted and self-hosted options.
Highlights:

  • User segments and remote config
  • API-first approach
  • Strong frontend and mobile SDK support
    It’s especially useful for teams working across web, mobile, and backend environments.

3. GrowthBook

GrowthBook is an A/B testing and feature flagging tool that’s lightweight and developer-friendly.
Highlights:

  • Easy integration
  • Detailed experiment analytics
  • Works well with React, Node, and Python
    It’s a perfect option for product teams focused on experimentation.

4. OpenFeature (Standard, Not a Platform)

OpenFeature is a CNCF standard that unifies feature flag APIs across vendors.
Why it matters:
You can switch between providers (LaunchDarkly, Flagsmith, Unleash) without rewriting your code. This brings long-term flexibility and reduces vendor lock-in.

How Feature Flags Work in Code

Here’s a simple example using LaunchDarkly (Node.js):

if (ldClient.variation("new-dashboard", user, false)) {
  renderNewDashboard();
} else {
  renderOldDashboard();
}

And with Unleash:

if (unleash.isEnabled("new-dashboard", user)) {
  renderNewDashboard();
} else {
  renderOldDashboard();
}

The logic stays the same: check the flag, then render the appropriate experience.

Best Practices for Feature Flagging

  • Clean up old flags often to prevent technical debt
  • Use naming conventions like ui.newDashboard or experiment.checkoutV2
  • Never store sensitive logic inside flag names
  • Keep flags short-lived unless they are configuration toggles
  • Log flag evaluations for debugging
  • Use consistent environments (dev, staging, prod)
  • Document flag purposes in your repository

Following these habits ensures that flags improve your workflow instead of cluttering it.

Common Pitfalls

  • Leaving flags in production code forever
  • Using flags for long-term logic that should be configuration
  • Mixing experiment flags and release flags
  • Adding too many flags without monitoring them
  • Not providing default values in code
  • Forgetting to secure flag APIs

By avoiding these mistakes, you maintain a clean, predictable flagging system.

Final Thoughts

Feature flagging gives teams a safer, smarter way to deploy. With tools like LaunchDarkly, Unleash, Flagsmith, or GrowthBook, you can ship features gradually, test safely, and react instantly when issues arise. Whether you choose a fully managed platform or an open-source alternative, feature flags help you reduce risk and increase flexibility during development. For related topics, explore Blue/Green vs Canary Deployments: When and How to Use Each to learn how flags support progressive delivery. For documentation, visit the LaunchDarkly developer guide.

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