ECS & Fargate

ECS (Elastic Container Service) is AWS’s container orchestrator. Fargate is the serverless capacity mode that runs containers without you managing EC2.

Concepts

• Task definition — the blueprint: container image(s), CPU/memory, ports, env, log config, and IAM task role.
• Task — a running instantiation of a task definition.
• Service — keeps N tasks running, integrates with a load balancer, and handles rollouts + autoscaling.
• Cluster — logical grouping of tasks/services and (for EC2 mode) the container instances.

Launch Types

	Fargate	EC2
You manage	Nothing (serverless)	The EC2 instances
Pricing	Per task vCPU/mem per second	Per EC2 instance
Best for	Spiky/variable, low-ops	Steady high utilization, GPUs, custom AMIs

Default to Fargate unless you need instance-level control or cheaper steady-state density.

Networking & Roles

• awsvpc mode (required for Fargate) gives each task its own ENI + security group.
• Task role = permissions for your app code. Execution role = permissions for the agent to pull images and write logs.
• Integrates with ALB/NLB; Service Connect / Cloud Map for service-to-service discovery.

Choosing Among Compute

• Lambda — event-driven, sub-15-min, no container ops, scales to zero.
• ECS/Fargate — long-running services, full container control, no Kubernetes overhead.
• EKS (Kubernetes) — when you need the Kubernetes ecosystem/portability.

Snippets

# Force a new deployment (pick up :latest image)
aws ecs update-service --cluster my-cluster \
  --service my-svc --force-new-deployment
 
# Run a one-off task on Fargate
aws ecs run-task --cluster my-cluster --launch-type FARGATE \
  --task-definition my-job \
  --network-configuration 'awsvpcConfiguration={subnets=[subnet-abc],securityGroups=[sg-123],assignPublicIp=DISABLED}'