What is ECS in AWS?

ECS stands for Amazon Elastic Container Service.
It is a fully managed container orchestration service provided by Amazon Web Services.

In simple terms
ECS helps you run, manage, and scale Docker containers on AWS without worrying about the underlying infrastructure.

If Docker is about building containers, ECS is about running them in production.

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Why do we need ECS?

Without ECS

• You manually run containers on EC2

• You manage scaling, restarts, failures

With ECS

• AWS schedules containers automatically

• Handles container failures

• Easy scaling and load balancing

• Integrated with IAM, ECR, CloudWatch

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ECS core components (very important)

1. Cluster

A logical group where containers run.

Example:

my-ecs-cluster

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2. Task Definition

Blueprint of your container.

Defines:

• Docker image (from ECR)

• CPU and memory

• Port mappings

• Environment variables

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3. Task

A running instance of a task definition.

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4. Service

Keeps tasks running continuously.

Example:

Run 2 containers all the time.

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5. Launch Types

EC2 Launch Type

• You manage EC2 instances

• You install ECS agent

• More control

Fargate Launch Type

• No EC2 management

• Serverless containers

• Pay only for runtime

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ECS vs Kubernetes (quick)

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Real-life example

You have:

• Spring Boot app

• Docker image in ECR

• Want to deploy it on AWS

Flow:

Git → Jenkins → Docker image → ECR → ECS → Load Balancer → Users

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ECS Setup Step by Step (using Fargate)

Prerequisites

• AWS account

• Docker image pushed to ECR

• IAM role for ECS

• VPC with subnets

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Step 1: Create ECS Cluster

1. Go to ECS Console

2. Click Create Cluster

3. Select Networking only (Fargate)

4. Cluster name: demo-ecs-cluster

5. Create cluster

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Step 2: Create Task Definition

1. Go to Task Definitions

2. Create new → Fargate

3. Configure:

   • Task name: demo-task

   • CPU: 0.5 vCPU

   • Memory: 1 GB

4. Container config:

   • Image: 123456789012.dkr.ecr.ap-south-1.amazonaws.com/my-app:latest

   • Port: 8080

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Step 3: Create Service

1. Create service from task definition

2. Launch type: Fargate

3. Service name: demo-service

4. Number of tasks: 1

5. Networking:

   • Public IP: Enabled

   • Security group: allow 8080

6. Create service

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Step 4: Access Application

Use public IP or ALB DNS:

http://<public-ip>:8080

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ECS with EC2 (short)

• Create EC2 with ECS-optimized AMI

• Register EC2 to ECS cluster

• Run tasks on EC2 capacity

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ECS Pricing (idea)

• Fargate: Pay per CPU & memory used

• EC2: Pay for EC2 instances

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Common interview lines

• ECS is AWS-managed container orchestration

• Task Definition defines container config

• Service ensures desired number of tasks

• Fargate removes server management

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When to use ECS?

• You are on AWS

• You want simple container orchestration

• You don’t want Kubernetes complexity