Graceful shutdown handling in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to listen for the shutdown signal.

Node.js

process.on('[1]', () => {
  console.log('Shutdown signal received');
});

Drag options to blanks, or click blank then click option'

ASIGINT

BSTART

CRUN

DEXIT

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'EXIT' instead of 'SIGINT' for the shutdown signal.

Confusing signal names like 'START' or 'RUN'.

The SIGINT signal is sent when you press Ctrl+C in the terminal, which is commonly used to trigger graceful shutdown.

2fill in blank

medium

Complete the code to close the HTTP server on shutdown.

Node.js

server.[1](() => {
  console.log('Server closed');
});

Drag options to blanks, or click blank then click option'

Aclose

Bstop

Cshutdown

Dend

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'stop' or 'shutdown' which are not valid server methods.

Using 'end' which is for streams, not servers.

The close method stops the server from accepting new connections and waits for existing connections to finish.

3fill in blank

hard

Fix the error in the shutdown handler to exit the process after closing the server.

Node.js

process.on('SIGTERM', () => {
  server.close(() => {
    [1](0);
  });
});

Drag options to blanks, or click blank then click option'

Aclose

Bstop

Cshutdown

Dexit

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'stop' or 'shutdown' which are not Node.js process methods.

Using 'close' which is a server method, not a process method.

The process.exit(0) command cleanly exits the Node.js process with a success code.

4fill in blank

hard

Fill both blanks to handle multiple shutdown signals and close the server.

Node.js

['SIGINT', '[1]'].forEach(signal => {
  process.on(signal, () => {
    server.[2](() => {
      console.log(`${signal} received, server closed.`);
      process.exit(0);
    });
  });
});

Drag options to blanks, or click blank then click option'

ASIGTERM

BSIGSTART

Cshutdown

Dclose

Attempts:

3 left

💡 Hint

Common Mistakes

Using invalid signal names like 'SIGSTART'.

Using wrong server methods like 'shutdown' instead of 'close'.

SIGTERM is another common shutdown signal. The server's close method stops it gracefully.

5fill in blank

hard

Fill all three blanks to log shutdown start, close server, and log shutdown complete.

Node.js

process.on('SIGINT', () => {
  console.log('[1]');
  server.[2](() => {
    console.log('[3]');
    process.exit(0);
  });
});

Drag options to blanks, or click blank then click option'

AShutdown starting

Bclose

CShutdown complete

DShutdown failed

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong messages that don't match the shutdown steps.

Using wrong server methods like 'stop' instead of 'close'.

Logging before and after closing the server helps track the shutdown process. The server is closed with close.

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