implement-graceful-shutdown-for-your-application

description: Use Effect.runFork and OS signal listeners to implement graceful shutdown for long-running applications. globs: "**/*.ts" alwaysApply: true

Implement Graceful Shutdown for Your Application

Rule: Use Effect.runFork and OS signal listeners to implement graceful shutdown for long-running applications.

Example

This example creates a server with a "scoped" database connection. It uses runFork to start the server and sets up a SIGINT handler to interrupt the server fiber, which in turn guarantees the database finalizer is called.

import { Effect, Layer, Fiber, Context, Scope } from "effect";
import * as http from "http";

// 1. A service with a finalizer for cleanup
class Database extends Effect.Service<Database>()("Database", {
  effect: Effect.gen(function* () {
    yield* Effect.log("Acquiring DB connection");
    return {
      query: () => Effect.succeed("data"),
    };
  }),
}) {}

// 2. The main server logic
const server = Effect.gen(function* () {
  const db = yield* Database;

  // Create server with proper error handling
  const httpServer = yield* Effect.sync(() => {
    const server = http.createServer((_req, res) => {
      Effect.runFork(
        Effect.provide(
          db.query().pipe(Effect.map((data) => res.end(data))),
          Database.Default
        )
      );
    });
    return server;
  });

  // Add a finalizer to close the server
  yield* Effect.addFinalizer(() =>
    Effect.gen(function* () {
      httpServer.close();
      yield* Effect.log("Server closed");
    })
  );

  // Start server with error handling
  yield* Effect.async<void, Error>((resume) => {
    httpServer.once("error", (err: Error) => {
      resume(Effect.fail(new Error(`Failed to start server: ${err.message}`)));
    });

    httpServer.listen(3456, () => {
      resume(Effect.succeed(void 0));
    });
  });

  yield* Effect.log("Server started on port 3456. Press Ctrl+C to exit.");

  // For testing purposes, we'll run for a short time instead of forever
  yield* Effect.sleep("2 seconds");
  yield* Effect.log("Shutting down gracefully...");
});

// 3. Provide the layer and launch with runFork
const app = Effect.provide(server.pipe(Effect.scoped), Database.Default);

// 4. Run the app and handle shutdown
Effect.runPromise(app).catch((error) => {
  Effect.runSync(Effect.logError("Application error: " + error));
  process.exit(1);
});