Graceful shutdown handling in Node.js - Mini Project: Build & Apply

Graceful Shutdown Handling in Node.js

📖 Scenario: You are building a simple Node.js server that needs to stop cleanly when the application is closed or restarted. This means it should finish any ongoing work and close resources properly before exiting.

🎯 Goal: Create a Node.js server that listens on port 3000 and handles shutdown signals gracefully by closing the server and logging a message before the program exits.

📋 What You'll Learn

Create a basic HTTP server using Node.js

Add a variable to track if the server is running

Implement a listener for shutdown signals like SIGINT

Close the server gracefully and log a shutdown message

💡 Why This Matters

🌍 Real World

Graceful shutdown is important for servers to close connections and free resources properly before stopping, avoiding data loss or corruption.

💼 Career

Many backend developer roles require knowledge of handling process signals and graceful shutdown to build reliable and maintainable server applications.

1

Create a basic HTTP server

Create a Node.js HTTP server using http.createServer that responds with 'Hello World' to any request. Make the server listen on port 3000.

Node.js

# Your code here to create the server and listen on port 3000

Hint

Use http.createServer to create the server and server.listen(3000) to start it.

2

Add a running state variable

Add a variable called isRunning and set it to true to track if the server is currently running.

Node.js

import http from 'http';

const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');
  res.end('Hello World');
});

server.listen(3000);

// Add a variable to track if the server is running
# Your code here

Hint

Declare let isRunning = true; after starting the server.

3

Listen for shutdown signals

Add a listener for the 'SIGINT' signal using process.on. Inside the listener, set isRunning to false and call server.close() to stop the server.

Node.js

import http from 'http';

const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');
  res.end('Hello World');
});

server.listen(3000);

let isRunning = true;

// Add a listener for SIGINT to handle graceful shutdown
# Your code here

Hint

Use process.on('SIGINT', () => { ... }) to listen for the shutdown signal.

4

Log shutdown completion

Add a listener for the server's 'close' event. Inside it, log 'Server has shut down gracefully.' and call process.exit(0) to exit the program cleanly.

Node.js

import http from 'http';

const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');
  res.end('Hello World');
});

server.listen(3000);

let isRunning = true;

process.on('SIGINT', () => {
  isRunning = false;
  server.close();
});

// Add a listener for the 'close' event to log shutdown and exit
# Your code here

Hint

Use server.on('close', () => { ... }) to handle the server closing event.

Practice

1. What is the main purpose of graceful shutdown in a Node.js application?

easy

A. To stop the app safely without losing data or leaving tasks unfinished

B. To restart the app automatically after a crash

C. To speed up the app startup time

D. To increase the app's memory usage

Solution

1. Step 1: Understand graceful shutdown concept

   Graceful shutdown means stopping the app carefully so it finishes ongoing work and saves data.

2. Step 2: Identify the purpose in options

   Only To stop the app safely without losing data or leaving tasks unfinished describes stopping safely without losing data or leaving tasks unfinished.

3. Final Answer:

   To stop the app safely without losing data or leaving tasks unfinished -> Option A

4. Quick Check:

   Graceful shutdown = safe stop without data loss [OK]

Hint: Graceful shutdown means stopping safely, not restarting or speeding up [OK]

Common Mistakes:

• Confusing graceful shutdown with app restart
• Thinking it improves startup speed
• Assuming it increases memory usage

2. Which Node.js code snippet correctly listens for the SIGINT signal to start graceful shutdown?

easy

A. process.on('SIGTERM', () => { console.log('Shutting down'); });

B. process.listen('SIGINT', () => { console.log('Shutting down'); });

C. process.on('SIGINT', () => { console.log('Shutting down'); process.exit(); });

D. process.signal('SIGINT', () => { console.log('Shutting down'); });

Solution

1. Step 1: Recall correct event listener syntax

   Node.js uses process.on('signal', callback) to listen for signals like SIGINT.

2. Step 2: Check options for correct syntax and signal

   process.on('SIGINT', () => { console.log('Shutting down'); process.exit(); }); uses process.on with 'SIGINT' and a callback, which is correct. process.on('SIGTERM', () => { console.log('Shutting down'); }); uses SIGTERM, which is valid but not SIGINT as asked. Options B and D use invalid methods.

3. Final Answer:

   process.on('SIGINT', () => { console.log('Shutting down'); process.exit(); }); -> Option C

4. Quick Check:

   Use process.on('SIGINT', callback) for SIGINT [OK]

Hint: Use process.on('SIGINT', callback) to handle Ctrl+C [OK]

Common Mistakes:

• Using process.listen instead of process.on
• Using process.signal which does not exist
• Confusing SIGINT with SIGTERM

3. Consider this code snippet:

const http = require('http');
const server = http.createServer((req, res) => {
  res.end('Hello');
});

process.on('SIGINT', () => {
  server.close(() => {
    console.log('Server closed');
    process.exit(0);
  });
});

server.listen(3000);

What happens when you press Ctrl+C in the terminal?

medium

A. The server immediately exits without closing connections

B. The server stops accepting new connections, logs 'Server closed', then exits

C. The server ignores Ctrl+C and keeps running

D. The server crashes with an error

Solution

1. Step 1: Understand SIGINT handler

   The code listens for SIGINT (Ctrl+C), then calls server.close to stop new connections and waits for existing ones to finish.

2. Step 2: Analyze server.close callback

   When server.close finishes, it logs 'Server closed' and calls process.exit(0) to exit cleanly.

3. Final Answer:

   The server stops accepting new connections, logs 'Server closed', then exits -> Option B

4. Quick Check:

   Ctrl+C triggers server.close then exit [OK]

Hint: SIGINT triggers server.close callback before exit [OK]

Common Mistakes:

• Thinking server exits immediately without closing
• Assuming Ctrl+C is ignored
• Expecting a crash error

4. This code aims to handle graceful shutdown but has a bug:

process.on('SIGINT', () => {
  server.close();
  console.log('Server closed');
  process.exit(0);
});

What is the problem?

medium

A. process.exit(0) runs before server.close finishes, causing abrupt exit

B. SIGINT event is not supported by process

C. console.log should be before server.close

D. server.close() does not exist on http server

Solution

1. Step 1: Understand asynchronous server.close

   server.close() is asynchronous and takes a callback to run after closing.

2. Step 2: Identify order of commands

   Here, process.exit(0) runs immediately after server.close() call, not waiting for close to finish, causing abrupt exit.

3. Final Answer:

   process.exit(0) runs before server.close finishes, causing abrupt exit -> Option A

4. Quick Check:

   Wait for server.close callback before exiting [OK]

Hint: Always exit inside server.close callback to wait for close [OK]

Common Mistakes:

• Calling process.exit too early
• Thinking SIGINT is unsupported
• Misunderstanding server.close existence

5. You want to handle both SIGINT and SIGTERM signals to gracefully shutdown your Node.js app. Which code correctly ensures the server closes once and exits safely without duplicate calls?

hard

A. process.on('SIGINT', () => server.close(() => process.exit(0)));
process.on('SIGTERM', () => server.close(() => process.exit(0)));

B. process.on('SIGINT', () => { console.log('Shutting down'); });
process.on('SIGTERM', () => { console.log('Shutting down'); });

C. process.on('SIGINT', () => { server.close(); process.exit(0); });
process.on('SIGTERM', () => { server.close(); process.exit(0); });

D. let isShuttingDown = false;
process.on('SIGINT', shutdown);
process.on('SIGTERM', shutdown);
function shutdown() {
if (isShuttingDown) return;
isShuttingDown = true;
server.close(() => {
console.log('Closed');
process.exit(0);
});
}

Solution

1. Step 1: Understand multiple signal handling

   Both SIGINT and SIGTERM can trigger shutdown, so we must avoid running shutdown twice.

2. Step 2: Check for duplicate shutdown prevention

   let isShuttingDown = false; process.on('SIGINT', shutdown); process.on('SIGTERM', shutdown); function shutdown() { if (isShuttingDown) return; isShuttingDown = true; server.close(() => { console.log('Closed'); process.exit(0); }); } uses a flag isShuttingDown to run shutdown only once, preventing duplicate server.close and exit calls.

3. Step 3: Analyze other options

   process.on('SIGINT', () => server.close(() => process.exit(0))); process.on('SIGTERM', () => server.close(() => process.exit(0))); calls server.close twice if both signals arrive. process.on('SIGINT', () => { server.close(); process.exit(0); }); process.on('SIGTERM', () => { server.close(); process.exit(0); }); calls process.exit immediately without waiting. process.on('SIGINT', () => { console.log('Shutting down'); }); process.on('SIGTERM', () => { console.log('Shutting down'); }); only logs without closing.

4. Final Answer:

   Code with a flag to prevent duplicate shutdown and safely close server once -> Option D

5. Quick Check:

   Use a flag to avoid duplicate shutdown calls [OK]

Hint: Use a flag to run shutdown logic only once for multiple signals [OK]

Common Mistakes:

• Calling server.close multiple times causing errors
• Exiting process before server closes
• Not handling both signals properly