Why microservices scale independently in NestJS - Visual Breakdown

Concept Flow - Why microservices scale independently

Client Request

↓

API Gateway

↓

Route to Specific Microservice

↓

Microservice Instance

↓

Process Request

↓

Return Response

↓

Scale Decision

↓

Add/Remove Instances of Microservice

↓

Independent Scaling Achieved

The client request goes through an API gateway, which routes it to the right microservice. Each microservice runs separately and can be scaled up or down on its own, without affecting others.

Execution Sample

NestJS

import { Controller, Get } from '@nestjs/common';

@Controller('orders')
export class OrdersController {
  @Get()
  getOrders() {
    return ['order1', 'order2'];
  }
}

A simple NestJS microservice controller that handles requests for orders independently.

Execution Table

Step	Action	Microservice Instance	Scaling Decision	Response
1	Client sends request to API Gateway	N/A	N/A	N/A
2	API Gateway routes to OrdersService	OrdersService Instance 1	N/A	N/A
3	OrdersService processes getOrders()	OrdersService Instance 1	N/A	['order1', 'order2']
4	High load detected on OrdersService	OrdersService Instance 1	Scale up: Add Instance 2	N/A
5	New request routed to OrdersService Instance 2	OrdersService Instance 2	N/A	['order1', 'order2']
6	Load normalizes	OrdersService Instances 1 & 2	Scale down: Remove Instance 2	N/A
7	Request routed to OrdersService Instance 1	OrdersService Instance 1	N/A	['order1', 'order2']

💡 Scaling decisions allow adding or removing microservice instances independently based on load.

Variable Tracker

Variable	Start	After Step 4	After Step 6	Final
OrdersService Instances	1	2	1	1
Load on OrdersService	Normal	High	Normal	Normal

Key Moments - 2 Insights

Why does scaling one microservice not affect others?

Because each microservice runs as a separate instance, scaling decisions (like adding or removing instances) apply only to that microservice, as shown in steps 4 and 6 of the execution_table.

How does the API Gateway help in independent scaling?

The API Gateway routes requests to specific microservice instances, so when new instances are added or removed, it directs traffic accordingly without changing other services (see steps 2 and 5).

Visual Quiz - 3 Questions

Look at the execution_table, how many OrdersService instances exist after step 4?

A 2

B 0

C 1

D 3

💡 Hint

Check the 'Microservice Instance' and 'Scaling Decision' columns at step 4.

At which step does the system scale down the OrdersService instances?

A Step 5

B Step 6

C Step 3

D Step 7

💡 Hint

Look for 'Scale down' in the 'Scaling Decision' column.

If the API Gateway did not route requests properly, what would happen?

A Microservices would scale automatically

B All microservices would scale together

C Requests might not reach the correct microservice instance

D Load would decrease

💡 Hint

Refer to the role of API Gateway in steps 2 and 5.

Concept Snapshot

Microservices run as separate services.
API Gateway routes requests to each microservice.
Each microservice can add or remove instances alone.
Scaling decisions depend on load per microservice.
This allows independent scaling without affecting others.

Full Transcript

In microservices architecture, each service runs independently. When a client sends a request, it goes through an API Gateway that directs it to the correct microservice instance. Each microservice can process requests on its own. When load increases on one microservice, new instances of that service can be added without changing others. When load decreases, instances can be removed. This independent scaling is possible because microservices are separate and the API Gateway manages routing. This example shows an OrdersService handling requests and scaling up and down based on load.