AWS Container Services — ECS, EKS, ECR

Amazon ECS (Elastic Container Service)

Container Orchestration: Manages Docker containers on a cluster of EC2 instances. ECS handles scheduling, scaling, and lifecycle management without requiring Kubernetes expertise.

Task Definitions: Blueprint describing how to run a Docker container—specifies the image, CPU, memory, environment variables, port mappings, and logging configuration.

Clusters: Logical grouping of EC2 instances where tasks run. You manage the underlying EC2 fleet, or let Fargate handle infrastructure.

Services: Ensure a specified number of tasks run continuously and handle task replacement if they fail. A Service is not a Task—the Service manages the desired state, while a Task is a single running instance of the definition.

Interview Angle

ECS launch type question: EC2 launch type = you manage the EC2 instances. Fargate launch type = AWS manages the infra, you define CPU/memory in the task definition. Fargate = serverless containers.

Common Gotchas

ECS Service is NOT a Task — a Service keeps N tasks running; a Task is a single running instance of the definition.

Amazon EKS (Elastic Kubernetes Service)

Managed Kubernetes: Simplifies running Kubernetes on AWS without needing to manage the Kubernetes control plane. AWS handles the master node; you focus on worker nodes and pods.

Node Management: Supports both EC2 and Fargate nodes. Use EC2 for full Kubernetes flexibility; use Fargate for serverless pod execution.

Integration: Integrates with AWS services like IAM, CloudWatch, and ALB. Deploy applications using standard Kubernetes manifests and tools.

Interview Angle

EKS vs ECS: EKS = Kubernetes (portable, complex, industry standard). ECS = AWS-native (simpler, tighter AWS integration). Interviewers ask: “when would you choose one over the other?” EKS if you need Kubernetes expertise or multi-cloud portability; ECS if you want simplicity and tight AWS integration.

Amazon Elastic Container Registry (ECR)

Managed Docker Container Registry: Store, manage, and deploy Docker container images in AWS with automatic replication, versioning, and access control.

Integration: Seamlessly integrates with Amazon ECS, EKS, and AWS Lambda. Reference ECR images via IAM role-based access—no credential management in task definitions.

Security: Provides encryption at rest and in transit, IAM roles for access control, and image scanning for vulnerabilities. Scan on push or pull.

Scalability: Automatically scales to meet your storage needs. Registry URLs are region-specific—cross-region replication is not automatic but available via replication rules.

Interview Angle

ECR lifecycle policies auto-delete old images. Without them, your registry fills up and costs grow. Always add a lifecycle policy — it’s an exam best practice AND a real-world gotcha.

Common Gotchas

ECR image URIs are region-specific — cross-region replication is not automatic.

Key Takeaways

Key Takeaways

• ECS Fargate = serverless containers (no EC2 to manage)
• ECS Task Definition = the blueprint (image, CPU, memory, env vars, ports)
• EKS = managed Kubernetes; bring your own K8s knowledge
• ECR = private Docker registry; integrate with ECS/EKS via IAM roles

Common Gotchas

• Fargate doesn’t support all instance types or GPU workloads (use EC2 launch type for those)
• ECR image URIs are region-specific — cross-region replication is not automatic