LaunchDarkly flags now sync to Vercel Edge Config

Vercel has released an integration with LaunchDarkly that lets teams read feature flag configurations from Edge Config, Vercel’s globally replicated data store. The goal is to give frontend applications low-latency access to flags without adding an HTTP round trip to a feature management service on every request.

Feature flags let teams ship code progressively and run experiments, but the value depends on how fast flag values can be read. Vercel positions Edge Config as a strong fit for that workload because data is pushed to every Vercel region at write time, before any requests arrive. Reads then happen directly from a Vercel Function or Edge Middleware, with most lookups returning in 5 ms or less and 99% of reads completing in under 15 ms.

Beyond feature flags, Edge Config is also suited for A/B testing data, complex dynamic redirects, and request blocking rules that need to change without a redeploy.

How the integration works

The LaunchDarkly integration is available to Enterprise customers and syncs flag configurations from LaunchDarkly into Edge Config. Working alongside the @launchdarkly/vercel-server-sdk package, the integration bootstraps a LaunchDarkly client from those synced flags. The client then reads from Edge Config instead of calling LaunchDarkly at request time, so flags are available immediately.

That distinction matters in serverless compute, where the runtime is short-lived. Unlike a long-running server, a serverless function cannot fetch a flag configuration once and keep a subscription open for updates. Reading from a locally replicated store avoids the overhead of fetching flag configurations over HTTP on every invocation.

Joyn, a streaming platform, is using the combination in production. The integration allows the team to update feature flag configurations and have them pushed automatically to Edge Config in real time, changing UI behavior without redeploying.

"The combination of Vercel Edge Config and the LaunchDarkly integration for Vercel lets us update our feature flagging configurations comfortably and automatically push them to our Edge Config store in real time. We are able to change the UI and behavior of our application without the need to re-deploy, which keeps us highly flexible. The low latency that Edge Config provides reduces the overhead of fetching flag configurations over HTTP, allowing us to have minimal latency and create a better experience for our users."

— Vincent Derks, Lead Engineer at Joyn

Getting started

Developers can install the LaunchDarkly integration from the Vercel marketplace, use the feature flag template for Next.js, or consult the Edge Config documentation for more details on supported integrations.