Graceful shutdown handling in Node.js - Step-by-Step Execution

Concept Flow - Graceful shutdown handling

Start Server

↓

Server Running

↓

Receive Shutdown Signal

↓

Stop Accepting New Requests

↓

Finish Ongoing Requests

↓

Close Server & Cleanup

↓

Exit Process

The server starts and runs normally until it receives a shutdown signal, then it stops new requests, finishes ongoing ones, cleans up, and exits.

Execution Sample

Node.js

const http = require('http');
const app = (req, res) => {
  res.end('Hello World');
};
const server = http.createServer(app);
server.listen(3000);

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

This code starts a server and listens for a shutdown signal to close the server gracefully before exiting.

Execution Table

Step	Event	Server State	Action Taken	Process State
1	Start server	Listening on port 3000	Server starts accepting requests	Running
2	Server running	Listening on port 3000	Handles incoming requests normally	Running
3	Receive SIGINT (Ctrl+C)	Listening on port 3000	Stop accepting new requests	Running
4	Finish ongoing requests	Closing server	Waits for all requests to finish	Running
5	Server closed	Closed	Cleanup done	Ready to exit
6	Process exit	N/A	Process exits with code 0	Exited

💡 Process exits after server closes and cleanup completes

Variable Tracker

Variable	Start	After SIGINT	After Close Callback	Final
server.listening	true	false	false	false
process.running	true	true	true	false

Key Moments - 2 Insights

Why does the server stop accepting new requests after receiving SIGINT?

Because in step 3 of the execution_table, the server.close() method is called, which stops new connections but allows ongoing requests to finish.

What happens if we call process.exit() immediately without waiting for server.close()?

The server might terminate abruptly, dropping ongoing requests. The execution_table shows the importance of waiting for the close callback before exiting (step 4 and 5).

Visual Quiz - 3 Questions

Look at the execution_table, what is the server state right after receiving SIGINT?

A Closing server

B Listening on port 3000

C Closed

D Not started

💡 Hint

Check row 3 under 'Server State' in the execution_table

At which step does the process exit in the execution_table?

A Step 6

B Step 4

C Step 5

D Step 3

💡 Hint

Look at the 'Process State' column for the exit event

If the server never finishes ongoing requests, what will happen to the process exit?

A Process exits immediately

B Process exits with error

C Process waits indefinitely

D Process restarts automatically

💡 Hint

Refer to step 4 where server waits for ongoing requests before closing

Concept Snapshot

Graceful shutdown in Node.js:
- Listen for shutdown signals (e.g., SIGINT)
- Call server.close() to stop new requests
- Wait for ongoing requests to finish
- Cleanup resources
- Exit process after server closes
This prevents dropping active connections.

Full Transcript

This visual execution shows how a Node.js server handles graceful shutdown. The server starts and listens for requests. When it receives a shutdown signal like SIGINT, it stops accepting new requests but keeps handling ongoing ones. Once all requests finish, the server closes and cleans up resources. Finally, the process exits cleanly. This prevents abrupt termination and dropped connections.