LaunchDarkly architecture
Overview
This topic gives a high-level explanation of LaunchDarkly’s platform architecture. You may want to read this topic if you are a developer considering implementing LaunchDarkly in your project, or an administrator who wants to understand how LaunchDarkly interacts with your app. If you’re an end user of the LaunchDarkly user interface (UI), you may not need to know what’s explained in this topic.
How LaunchDarkly connects to your application
Your application uses a LaunchDarkly SDK to connect to LaunchDarkly’s flag delivery network, and uses that connection to evaluate and serve specific feature flag variations to specific contexts with any attributes you specify. You can use context attributes to target individuals, device types, geographic regions, infrastructure components, operating system versions, and more. This is true regardless of whether LaunchDarkly serves the flag variation to a desktop, laptop, or mobile device. LaunchDarkly SDKs are available in dozens of languages. To learn more, read SDKs.
The flag delivery network is comprised of a third-party content delivery network (CDN) and LaunchDarkly's distributed core architecture components. LaunchDarkly's core architecture is secure, highly available, and spans multiple cloud availability zones, which enables fast responses and consistent experiences anywhere in the world.
How your application receives flag values
In your application, the LaunchDarkly SDK retrieves the current set of feature flag values from LaunchDarkly. If the SDK is unable to reach LaunchDarkly, it can fall back to default flag values that you define within your application code. Optionally, you can use the LaunchDarkly Relay Proxy to provide even more availability. To learn more, read Optional components of a LaunchDarkly installation.
When you integrate a LaunchDarkly SDK with your app, flag evaluation can begin. After the application launches, the LaunchDarkly SDK initializes within that application code. When it initializes, the SDK fetches the initial feature flag payload and makes it available to the application. This payload is stored and evaluated in your application memory, which gives the app near-instant access to flag variations. The SDK then sends information about flag evaluations back to LaunchDarkly. If LaunchDarkly is unreachable, the SDK can access in-app fallback flag values that you specify.
When you update a flag’s targeting rules, the update is sent through LaunchDarkly’s streaming infrastructure directly to all connected SDKs. While updates stream by default, some environments may not support persistent connections or may prefer not to maintain them—such as mobile apps where long-lived connections could consume end users’ limited data. In those cases, LaunchDarkly SDKs can fall back to polling mode to receive flag updates.
There are several different types of LaunchDarkly SDKs that can connect your application to LaunchDarkly, including server-side SDKs, client-side SDKs, edge SDKs, AI SDKs, and more. Client-side SDKs support both mobile devices and browsers. To learn more about how each type of SDK works, read Client-side, server-side, and edge SDKs.
Optional components of a LaunchDarkly installation
In addition to LaunchDarkly’s built-in core architecture, two optional components are available for you to configure. You do not have to use either of these components, but if you do, you can use either or both. Whatever you choose, you install and configure the components, and you control the data that flows in or out of them.
The Relay Proxy is an optional component that provides a cache of flag values for a LaunchDarkly environment. To learn more, read The Relay Proxy.
Data Export is an optional feature that allows you to stream event data to different destination services so you can analyze information using your preferred tools. To learn more, read Data Export.
