TCP transport in NestJS - Performance & Optimization

Performance: TCP transport

MEDIUM IMPACT

This affects the speed and responsiveness of backend communication between microservices or clients and servers using TCP protocol.

Sending messages between microservices using NestJS TCP transport

NestJS

const client = new ClientTCP({ host: 'localhost', port: 3000 });
await client.connect();
const response1 = await client.send('event1', { data1 }).toPromise();
const response2 = await client.send('event2', { data2 }).toPromise();
// reuse client without reconnecting
await client.close();

Reusing a single TCP client connection avoids repeated handshakes and reduces latency.

📈 Performance Gainreduces latency by 100-200ms per message, improves throughput

Sending messages between microservices using NestJS TCP transport

NestJS

const client = new ClientTCP({ host: 'localhost', port: 3000 });
await client.connect();
const response = await client.send('event', { data }).toPromise();
await client.close();

Creating and closing the TCP client for every message causes repeated connection overhead and delays.

📉 Performance Costadds 100-200ms latency per message due to TCP handshake and teardown

Performance Comparison

Pattern	Connection Overhead	Latency per Message	Resource Usage	Verdict
Create and close client per message	High (new TCP handshake each time)	High (100-200ms extra)	High CPU and network usage	[X] Bad
Reuse persistent client connection	Low (single handshake)	Low (minimal extra latency)	Lower CPU and network usage	[OK] Good

Rendering Pipeline

TCP transport in NestJS involves establishing a socket connection, sending data packets, and receiving responses asynchronously. The main bottleneck is the network handshake and socket management.

→Connection Establishment

→Data Transmission

→Response Handling

⚠️ BottleneckConnection Establishment due to TCP handshake overhead

Optimization Tips

1Reuse TCP client connections to avoid repeated handshakes.

2Avoid creating and closing TCP clients for every message.

3Monitor TCP connections to detect unnecessary reconnections.

Performance Quiz - 3 Questions

What is the main performance cost of creating a new TCP client for every message in NestJS?

A Repeated TCP handshakes causing latency

B Increased memory usage on the client

C Slower JavaScript execution

D More database queries

DevTools: Network panel in backend monitoring tools or tcpdump

How to check: Capture TCP packets during message sending; check for repeated connection setups and teardowns.

What to look for: Multiple TCP handshakes indicate inefficient connection reuse; persistent connections show fewer handshakes and lower latency.

Practice

1. What is the main purpose of using Transport.TCP in a NestJS microservice?

easy

A. To connect to a database using TCP.

B. To serve static files over HTTP.

C. To enable communication between microservices using TCP sockets.

D. To handle WebSocket connections.

Solution

1. Step 1: Understand the role of Transport.TCP

   Transport.TCP is used in NestJS to set up microservices communication over TCP sockets.

2. Step 2: Compare with other options

   Serving static files, database connections, and WebSocket handling are different concerns not related to Transport.TCP.

3. Final Answer:

   To enable communication between microservices using TCP sockets. -> Option C

4. Quick Check:

   Transport.TCP = Microservice TCP communication [OK]

Hint: Remember TCP transport is for microservice socket communication [OK]

Common Mistakes:

• Confusing TCP transport with HTTP or WebSocket protocols
• Thinking it handles database connections
• Assuming it serves static files

2. Which of the following is the correct way to create a TCP microservice in NestJS?

easy

A. const app = await NestFactory.createMicroservice(AppModule, { protocol: Transport.TCP, port: 3000 });

B. const app = await NestFactory.createMicroservice(AppModule, { transport: Transport.TCP, options: { port: 3000 } });

C. const app = await NestFactory.createMicroservice(AppModule, { transport: 'tcp', port: 3000 });

D. const app = await NestFactory.createMicroservice(AppModule, { transport: Transport.HTTP, options: { port: 3000 } });

Solution

1. Step 1: Check NestJS microservice creation syntax

   The correct syntax uses transport: Transport.TCP and an options object with port.

2. Step 2: Identify incorrect options

   The other options use wrong properties like protocol instead of transport, pass port directly without an options object, use string 'tcp' instead of the Transport.TCP enum, or use the wrong transport type like Transport.HTTP.

3. Final Answer:

   const app = await NestFactory.createMicroservice(AppModule, { transport: Transport.TCP, options: { port: 3000 } }); -> Option B

4. Quick Check:

   Use transport: Transport.TCP with options object [OK]

Hint: Use Transport.TCP enum and options object for port [OK]

Common Mistakes:

• Using 'protocol' instead of 'transport'
• Passing port directly without options object
• Using string 'tcp' instead of Transport.TCP enum
• Confusing TCP with HTTP transport

3. Given this NestJS TCP microservice setup:

const app = await NestFactory.createMicroservice(AppModule, {
  transport: Transport.TCP,
  options: { host: '127.0.0.1', port: 4000 }
});
await app.listen();
console.log('Microservice is listening');

What will be the output when the microservice starts successfully?

medium

A. Microservice failed to start

B. Error: Port 4000 is already in use

C. Listening on HTTP port 4000

D. Microservice is listening

Solution

1. Step 1: Understand the code flow

   The microservice is created with TCP transport on host 127.0.0.1 and port 4000, then listens successfully.

2. Step 2: Identify the console output

   After await app.listen(), the console logs 'Microservice is listening'. No errors are shown.

3. Final Answer:

   Microservice is listening -> Option D

4. Quick Check:

   Successful listen logs message [OK]

Hint: Successful listen logs 'Microservice is listening' [OK]

Common Mistakes:

• Assuming automatic HTTP server start
• Expecting error without port conflict
• Confusing TCP with HTTP output

4. Identify the error in this NestJS TCP microservice code:

const app = await NestFactory.createMicroservice(AppModule, {
  transport: Transport.TCP,
  options: { port: '3000' }
});
await app.listen();

medium

A. Port should be a number, not a string.

B. Missing host option causes failure.

C. Transport.TCP is invalid here.

D. app.listen() must be called with a callback.

Solution

1. Step 1: Check the options object

   The port value is given as a string '3000', but it must be a number.

2. Step 2: Validate other parts

   Host is optional, Transport.TCP is valid, and app.listen() can be awaited without callback.

3. Final Answer:

   Port should be a number, not a string. -> Option A

4. Quick Check:

   Port must be numeric type [OK]

Hint: Port option must be a number, not quoted string [OK]

Common Mistakes:

• Passing port as string instead of number
• Thinking host is mandatory
• Expecting app.listen to require callback

5. You want to create a NestJS TCP microservice that listens on all network interfaces on port 5000 and logs a message when a client connects. Which code snippet correctly implements this?

hard

A. const app = await NestFactory.createMicroservice(AppModule, { transport: Transport.TCP, options: { host: '0.0.0.0', port: 5000 } });
await app.listen();
app.on('connection', () => console.log('Client connected'));

B. const app = await NestFactory.createMicroservice(AppModule, { transport: Transport.TCP, options: { host: '0.0.0.0', port: 5000 } });
app.listen(() => console.log('Client connected'));

C. const app = await NestFactory.createMicroservice(AppModule, { transport: Transport.TCP, options: { host: 'localhost', port: 5000 } });
app.listen(() => console.log('Client connected'));

D. const app = await NestFactory.createMicroservice(AppModule, { transport: Transport.TCP, options: { port: 5000 } });
app.listen(() => console.log('Client connected'));

Solution

1. Step 1: Set host and port correctly

   To listen on all interfaces, host must be '0.0.0.0' and port 5000 is correct.

2. Step 2: Attach client connection event properly

   TCP microservice emits 'connection' event; attaching listener after await app.listen() is correct.

3. Step 3: Evaluate distractors

   Distractors either use the wrong host like 'localhost', omit the host, fail to await app.listen(), or attach the logger to the listen() callback instead of the 'connection' event.

4. Final Answer:

   const app = await NestFactory.createMicroservice(AppModule, { transport: Transport.TCP, options: { host: '0.0.0.0', port: 5000 } }); await app.listen(); app.on('connection', () => console.log('Client connected')); -> Option A

5. Quick Check:

   Host 0.0.0.0 + event listener after listen [OK]

Hint: Use host '0.0.0.0' and listen before event binding [OK]

Common Mistakes:

• Using 'localhost' instead of '0.0.0.0' to listen on all interfaces
• Logging inside listen callback instead of connection event
• Not awaiting app.listen() before event binding