# Express.js Graceful Shutdown ## Express.js Graceful Shutdown ```typescript import express from "express"; import http from "http"; class GracefulShutdownServer { private app: express.Application; private server: http.Server; private isShuttingDown = false; private activeConnections = new Set(); private shutdownTimeout = 30000; // 30 seconds constructor() { this.app = express(); this.server = http.createServer(this.app); this.setupMiddleware(); this.setupRoutes(); this.setupShutdownHandlers(); } private setupMiddleware(): void { // Track active connections this.app.use((req, res, next) => { if (this.isShuttingDown) { res.set("Connection", "close"); return res.status(503).json({ error: "Server is shutting down", }); } this.activeConnections.add(res); res.on("finish", () => { this.activeConnections.delete(res); }); res.on("close", () => { this.activeConnections.delete(res); }); next(); }); } private setupRoutes(): void { this.app.get("/health", (req, res) => { if (this.isShuttingDown) { return res.status(503).json({ status: "shutting_down" }); } res.json({ status: "ok" }); }); this.app.get("/api/data", async (req, res) => { // Simulate long-running request await new Promise((resolve) => setTimeout(resolve, 5000)); res.json({ data: "response" }); }); } private setupShutdownHandlers(): void { const signals: NodeJS.Signals[] = ["SIGTERM", "SIGINT"]; signals.forEach((signal) => { process.on(signal, () => { console.log(`Received ${signal}, starting graceful shutdown...`); this.gracefulShutdown(signal); }); }); // Handle uncaught exceptions process.on("uncaughtException", (error) => { console.error("Uncaught exception:", error); this.gracefulShutdown("UNCAUGHT_EXCEPTION"); }); process.on("unhandledRejection", (reason, promise) => { console.error("Unhandled rejection:", reason); this.gracefulShutdown("UNHANDLED_REJECTION"); }); } private async gracefulShutdown(signal: string): Promise { if (this.isShuttingDown) { console.log("Shutdown already in progress"); return; } this.isShuttingDown = true; console.log(`Starting graceful shutdown (${signal})`); // Set shutdown timeout const shutdownTimer = setTimeout(() => { console.error("Shutdown timeout reached, forcing exit"); process.exit(1); }, this.shutdownTimeout); try { // 1. Stop accepting new connections await this.stopAcceptingConnections(); // 2. Wait for active requests to complete await this.waitForActiveConnections(); // 3. Close server await this.closeServer(); // 4. Cleanup resources await this.cleanupResources(); console.log("Graceful shutdown completed"); clearTimeout(shutdownTimer); process.exit(0); } catch (error) { console.error("Error during shutdown:", error); clearTimeout(shutdownTimer); process.exit(1); } } private async stopAcceptingConnections(): Promise { console.log("Stopping new connections..."); return new Promise((resolve) => { this.server.close(() => { console.log("Server stopped accepting new connections"); resolve(); }); }); } private async waitForActiveConnections(): Promise { console.log( `Waiting for ${this.activeConnections.size} active connections...`, ); const checkInterval = 100; const maxWait = this.shutdownTimeout - 5000; let waited = 0; while (this.activeConnections.size > 0 && waited < maxWait) { await new Promise((resolve) => setTimeout(resolve, checkInterval)); waited += checkInterval; if (waited % 1000 === 0) { console.log( `Still waiting for ${this.activeConnections.size} connections...`, ); } } if (this.activeConnections.size > 0) { console.warn( `Force closing ${this.activeConnections.size} remaining connections`, ); this.activeConnections.forEach((res: any) => { res.destroy(); }); } console.log("All connections closed"); } private async closeServer(): Promise { // Server already closed in stopAcceptingConnections console.log("Server closed"); } private async cleanupResources(): Promise { console.log("Cleaning up resources..."); // Close database connections await this.closeDatabaseConnections(); // Flush logs await this.flushLogs(); // Close any other resources await this.closeOtherResources(); console.log("Resources cleaned up"); } private async closeDatabaseConnections(): Promise { // Close database connections console.log("Closing database connections..."); // await db.close(); } private async flushLogs(): Promise { // Flush any pending logs console.log("Flushing logs..."); } private async closeOtherResources(): Promise { // Close Redis, message queues, etc. console.log("Closing other resources..."); } start(port: number): void { this.server.listen(port, () => { console.log(`Server listening on port ${port}`); }); } } // Usage const server = new GracefulShutdownServer(); server.start(3000); ```

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