How do you implement an API Gateway pattern in NestJS that aggregates multiple microservices?

Q: How do you implement an API Gateway pattern in NestJS that aggregates multiple microservices?

@Controller('orders') export class OrdersGatewayController { constructor( @Inject('ORDERS_SERVICE') private ordersClient: ClientProxy, @Inject('USERS_SERVICE') private usersClient: ClientProxy, @Inject('PAYMENT_SERVICE') private paymentClient: ClientProxy, ) {} @Post() async createOrder(@Body() dto: CreateOrderDto, @CurrentUser() user: User) { // Sequential — each step depends on the previous result const order = await firstValueFrom( this.ordersClient.send({ cmd: 'create_order' }, { ...dto, userId: user.id }), ); const payment = await firstValueFrom( this.paymentClient.send({ cmd: 'charge' }, { orderId: order.id, amount: order.total }), ); return { order, payment }; } @Get(':id') async getOrderDetails(@Param('id') id: string) { // Parallel — independent calls run concurrently const [order, payment] = await Promise.all([ firstValueFrom(this.ordersClient.send({ cmd: 'get_order' }, { id })), firstValueFrom(this.paymentClient.send({ cmd: 'get_payment' }, { orderId: id })), ]); const user = await firstValueFrom( this.usersClient.send({ cmd: 'get_user' }, { id: order.userId }), ); return { order, user, payment }; } } Use Promise.all() for independent downstream calls — runs them in parallel and halves latency. Use sequential awaits only when each call depends on the result of the previous one. Apply a global RpcExceptionFilter to convert microservice errors to HTTP responses on the gateway. Add timeout operators (timeout(3000)) to prevent a slow service from hanging the gateway response. The gateway should be thin — business logic belongs in the downstream services, not the gateway.

Difficulty: 5/10

API Gateway, NestJS microservices, request aggregation

Create an HTTP-facing NestJS application that injects multiple ClientProxy instances — one per downstream service. Use sequential calls when each step depends on the previous result. Use Promise.all() for independent parallel calls. Map RpcException errors to appropriate HTTP exceptions using catchError() in the pipeline.

API Gateway controller aggregating multiple services

API Gateway design principles:

1
Use Promise.all() for independent downstream calls — runs them in parallel and halves latency.

How do you implement an API Gateway pattern in NestJS that aggregates multiple microservices?

Difficulty: 5/10

API Gateway, NestJS microservices, request aggregation

Create an HTTP-facing NestJS application that injects multiple ClientProxy instances — one per downstream service. Use sequential calls when each step depends on the previous result. Use Promise.all() for independent parallel calls. Map RpcException errors to appropriate HTTP exceptions using catchError() in the pipeline.

API Gateway controller aggregating multiple services

API Gateway design principles:

1
Use Promise.all() for independent downstream calls — runs them in parallel and halves latency.

How do you implement an API Gateway pattern in NestJS that aggregates multiple microservices?

How do you implement an API Gateway pattern in NestJS that aggregates multiple microservices?

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