Graceful shutdown on errors in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when an uncaught exception occurs in this Node.js server?

Consider this Node.js server code snippet. What will be the output behavior when an uncaught exception is thrown inside the request handler?

Node.js

import http from 'http';

const server = http.createServer((req, res) => {
  if (req.url === '/error') {
    throw new Error('Unexpected error');
  }
  res.end('Hello World');
});

server.listen(3000);

process.on('uncaughtException', (err) => {
  console.error('Caught exception:', err.message);
  // No server.close() called here
});

A The server logs the error message and shuts down immediately without closing connections.

B The server logs the error message but continues running and accepts new requests.

C The server crashes without logging anything.

D The server logs the error and gracefully closes existing connections before exiting.

💡 Hint

Think about what happens if you catch an uncaughtException but do not close the server.

The 'uncaughtException' handler logs the error but since server.close() is not called, the server keeps running and accepts new requests. This is risky because the server state may be unstable.

❓ state_output

intermediate

What is the state of the server after calling server.close() inside an error handler?

Given this code snippet, what is the state of the server after an error triggers the 'uncaughtException' handler that calls server.close()?

Node.js

import http from 'http';

const server = http.createServer((req, res) => {
  if (req.url === '/fail') {
    throw new Error('Fail');
  }
  res.end('OK');
});

server.listen(3000);

process.on('uncaughtException', (err) => {
  console.error('Error:', err.message);
  server.close(() => {
    console.log('Server closed');
    process.exit(1);
  });
});

A The server stops accepting new connections but keeps existing connections open until they finish.

B The server immediately terminates all connections and exits.

C The server continues accepting new connections during server.close().

D The server ignores server.close() and keeps running.

💡 Hint

Remember what server.close() does in Node.js.

Calling server.close() stops the server from accepting new connections but allows existing connections to complete before the callback runs.

🔧 Debug

advanced

Why does this graceful shutdown code not exit the process?

This code aims to gracefully shut down the server on an unhandled rejection but the process never exits. What is the cause?

Node.js

import http from 'http';

const server = http.createServer((req, res) => {
  if (req.url === '/reject') {
    Promise.reject(new Error('Rejected promise'));
  }
  res.end('OK');
});

server.listen(3000);

process.on('unhandledRejection', (reason) => {
  console.error('Unhandled rejection:', reason.message);
  server.close(() => {
    console.log('Server closed');
  });
  // Missing process.exit()
});

A The error is swallowed silently and does not trigger the handler.

B The server.close() callback never runs because the server is not listening.

C UnhandledRejection event does not catch promise rejections inside request handlers.

D The process does not exit because process.exit() is not called after server.close().

💡 Hint

Think about what happens after server.close() finishes.

Without calling process.exit(), the Node.js process keeps running even after the server closes, because there may be other open handles or timers.

📝 Syntax

advanced

Which option correctly handles graceful shutdown on SIGINT signal?

Choose the code snippet that correctly listens for SIGINT and gracefully shuts down the server before exiting.

A

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

B

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

C

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

D

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

💡 Hint

Remember server.close() is asynchronous and process.exit() should be called after it finishes.

Option A waits for server.close() to finish before calling process.exit(0), ensuring graceful shutdown. Other options call process.exit() too early or log before closing.

🧠 Conceptual

expert

Why is it risky to continue running a Node.js server after catching an uncaught exception without shutting down?

Select the best explanation for why continuing to run a Node.js server after an uncaught exception without shutting down can cause problems.

A Uncaught exceptions are always harmless and can be ignored safely.

B The server will automatically restart, so no action is needed.

C The server may be in an inconsistent state, leading to unpredictable behavior or security issues.

D Node.js prevents any further requests after an uncaught exception automatically.

💡 Hint

Think about what happens to program state after an unexpected error.

Uncaught exceptions can leave the server in an unstable state. Continuing to run risks corrupted data, memory leaks, or security vulnerabilities. It's best to shut down and restart cleanly.