LaunchDarkly

LaunchDarkly is a feature management platform that decouples code deployments from feature releases using feature flags. Instead of deploying code to release features, teams wrap new features in flags and toggle them on/off remotely without redeploying. This enables progressive rollouts (10% of users, then 50%, then 100%), A/B testing, instant rollbacks, and targeted releases (show feature only to beta users or specific segments).

Best for: Product and engineering teams at companies practicing continuous delivery who want to deploy code daily while controlling feature releases separately. Particularly valuable for reducing deployment risk in critical systems, running controlled experiments, or personalizing experiences per user segment. Teams running microservices or mobile apps appreciate the ability to coordinate feature releases across services.

Common Questions

How do feature flags work in LaunchDarkly?
In your code, you wrap new features in an if/else block checking a LaunchDarkly flag: if (launchDarkly.variation('new-checkout', false)) { /* new code */ }. The flag state is controlled remotely via LaunchDarkly's dashboard. Flags can be simple on/off toggles, percentage rollouts, or complex targeting rules (show to users in US with premium accounts). SDKs cache flag states locally for millisecond evaluation.

What is progressive delivery?
Progressive delivery means releasing features gradually—starting with internal users, then 5% of production traffic, then 25%, 50%, and eventually 100%. At each stage, you monitor metrics (errors, performance, conversions) before expanding. If issues arise, instantly roll back without touching code. This de-risks launches compared to "big bang" releases to all users at once.

Does LaunchDarkly support experimentation?
Yes, LaunchDarkly includes built-in experimentation for running A/B tests and measuring feature impact on metrics. Create experiments by serving different flag variations to user segments, then track how each variation performs on KPIs (conversion rate, revenue, engagement). Statistical analysis determines winning variations. Integrates with analytics tools for richer data.

What platforms does LaunchDarkly support?
LaunchDarkly has SDKs for JavaScript, React, Node.js, Python, Ruby, PHP, Java, .NET, Go, iOS, Android, React Native, Flutter, and more. Backend SDKs use streaming connections for real-time updates; mobile SDKs handle offline mode and reconnection. Also supports server-side SDKs for edge computing (Cloudflare Workers, Fastly Compute@Edge).

Pricing & Plans

• Starter: $10/seat/month (up to 10 seats), 1,000 monthly active users (MAU), unlimited flags, 14-day data retention
• Pro: $20/seat/month (unlimited seats), includes experimentation, 1,000 MAU included then $4/1,000 MAU
• Enterprise: Custom pricing, adds advanced targeting, unlimited environments, SAML/SSO, governance features

Most organizations pay $500-$5,000/month depending on MAU and features. Free 14-day trial available.

Limitations

• Monthly active user (MAU) costs scale: Applications with millions of users can incur significant costs at $4 per 1,000 MAU. Requires careful context management (don't send PII unnecessarily).
• Code coupling: Features become dependent on LaunchDarkly's SDK and service. If LaunchDarkly experiences an outage or your connection fails, flags default to fallback values (usually "off"), potentially hiding features.
• Flag debt: Without discipline, accumulating hundreds of old flags creates technical debt. Teams must actively clean up flags after features are fully rolled out to avoid codebase clutter.

Getting Started

1. Sign up at launchdarkly.com (14-day free trial, no credit card required)
2. Create a new project and environment (development, staging, production)
3. Install the LaunchDarkly SDK for your platform (npm, pip, gem, etc.)
4. Initialize the SDK in your application with your SDK key
5. Create your first feature flag in the dashboard (e.g., "new-homepage")
6. Wrap new code in flag evaluation: if (client.variation('new-homepage', false)) { ... }
7. Toggle the flag on/off remotely or configure progressive rollout percentages

Start with one simple boolean flag on a low-risk feature to learn the workflow before using flags for major launches.