Register a Fargate-compatible ECS task definition with awsvpc networking, valid CPU/memory, IAM roles, awslogs logging, and ARM64/Graviton runtime platform

Documented steps

1. Author a container definition JSON array with at minimum name, image, essential, portMappings, and a logConfiguration block; save as containers.json or inline it.
2. Choose a valid Fargate cpu/memory pair (see gotchas for the full table), e.g. cpu=256 (.25 vCPU) with memory=512 MiB, or cpu=1024 with memory up to 8192 MiB.
3. Create (or reuse) two IAM roles: an execution role (e.g. ecsTaskExecutionRole) with the AWS managed policy AmazonECSTaskExecutionRolePolicy attached, and a task role for your application's own AWS API calls.
4. Add a logConfiguration to each container using logDriver=awslogs with options awslogs-group, awslogs-region, awslogs-stream-prefix (optionally awslogs-create-group=true so ECS creates the log group automatically).
5. For Graviton/ARM64, add runtimePlatform with cpuArchitecture=ARM64 and operatingSystemFamily=LINUX, and make sure the container image itself is built for arm64.
6. Run: aws ecs register-task-definition --family my-app --network-mode awsvpc --requires-compatibilities FARGATE --cpu 256 --memory 512 --execution-role-arn arn:aws:iam::ACCOUNT:role/ecsTaskExecutionRole --task-role-arn arn:aws:iam::ACCOUNT:role/ecsTaskRole --container-definitions file://containers.json --runtime-platform cpuArchitecture=ARM64,operatingSystemFamily=LINUX
7. Confirm networkMode is awsvpc (the only mode Fargate supports) — RegisterTaskDefinition requires it whenever requiresCompatibilities includes FARGATE.
8. Verify with: aws ecs describe-task-definition --task-definition my-app and note the returned family:revision (e.g. my-app:3) for use in RunTask/CreateService.
9. Optionally attach resource tags with --tags key=Environment,value=Production (max 50 tags per resource).
10. Official docs: https://docs.aws.amazon.com/AmazonECS/latest/APIReference/API_RegisterTaskDefinition.html | https://docs.aws.amazon.com/AmazonECS/latest/developerguide/task-cpu-memory-error.html | https://docs.aws.amazon.com/AmazonECS/latest/developerguide/task_execution_IAM_role.html | https://docs.aws.amazon.com/AmazonECS/latest/developerguide/resource-initialization-error.html