Edge functions

Run TypeScript, Go, or Python at 280+ POPs with sub-30ms cold starts.

Edge functions run as close to your users as the network allows. Halo isolates each invocation in a V8 isolate (TS) or a microVM (Go/Python), and routes requests to the nearest healthy POP.

Create a function

api/hello.ts

export default function handler(req: Request) {
  return new Response("hi from " + req.headers.get("x-halo-region"));
}

The file path becomes the route. api/hello.ts is reachable at /api/hello after deploy.

Per-region pinning

By default, functions run in every POP. Pin to a region:

export const config = {
  regions: ["iad1", "fra1"],
};

Runtime: V8 isolates. Cold start: ~5–15ms. Memory: 128 MB max.

Runtime: Firecracker microVM. Cold start: ~25–50ms. Memory: up to 1 GB.

Runtime: Firecracker microVM. Cold start: ~30–60ms. Memory: up to 1 GB.

Streaming responses

export default async function handler() {
  const stream = new ReadableStream({
    start(controller) {
      controller.enqueue(new TextEncoder().encode("first chunk\n"));
      setTimeout(() => {
        controller.enqueue(new TextEncoder().encode("second chunk\n"));
        controller.close();
      }, 100);
    },
  });
  return new Response(stream);
}

Halo flushes each chunk to the client as soon as it’s enqueued.

Last updated 3 d ago Edit this page