Graceful shutdown handling in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is graceful shutdown in Node.js?

Graceful shutdown means closing the server and cleaning up resources properly before the app stops, so no requests are lost or data corrupted.

beginner

Which Node.js event is commonly used to detect when the process should shut down?

The 'SIGINT' signal is often used to detect when the user presses Ctrl+C to stop the process.

intermediate

Why should you stop accepting new requests during graceful shutdown?

Stopping new requests prevents the server from starting work it can't finish before shutting down, avoiding errors or lost data.

intermediate

How can you ensure all ongoing requests finish before the server closes?

You wait for all current requests to complete, often by tracking active connections and closing the server only after they finish.

intermediate

What is a common method to clean up resources during shutdown in Node.js?

Closing database connections, clearing timers, and releasing file handles are common cleanup steps during shutdown.

Which signal is typically used to trigger graceful shutdown in a Node.js app?

A SIGCONT

B SIGKILL

C SIGSTOP

D SIGINT

SIGINT is sent when you press Ctrl+C and is commonly used to start graceful shutdown.

What should a server do first when starting graceful shutdown?

A Stop accepting new requests

B Restart the server

C Exit the process

D Close database connections immediately

Stopping new requests prevents new work from starting during shutdown.

Why is it important to wait for ongoing requests to finish before shutdown?

A To restart the server faster

B To avoid losing data or breaking client connections

C To speed up shutdown

D To free memory immediately

Waiting ensures requests complete properly without errors.

Which Node.js method helps to stop the server from accepting new connections?

A server.close()

B server.listen()

C process.exit()

D server.open()

server.close() stops new connections but lets existing ones finish.

What is NOT a typical cleanup task during graceful shutdown?

A Closing database connections

B Clearing timers

C Opening new network sockets

D Releasing file handles

Opening new sockets is not part of shutdown; it would start new work.

Explain the steps to implement graceful shutdown in a Node.js server.

Think about what happens from signal to process exit.

Why is graceful shutdown important for a Node.js application?

Consider what happens if the app stops suddenly.

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