Launch a one-off ECS task on Fargate with RunTask, configure awsvpc networking, wait for it to stop, and read its container exit code

Documented steps

1. Decide launchType vs capacityProviderStrategy — RunTask accepts either but not both (mutually exclusive); for plain Fargate use --launch-type FARGATE.
2. Run: aws ecs run-task --cluster my-cluster --task-definition my-app:3 --launch-type FARGATE --network-configuration "awsvpcConfiguration={subnets=[subnet-12345678],securityGroups=[sg-12345678],assignPublicIp=ENABLED}" --count 1
3. For awsvpc-mode task definitions, networkConfiguration.awsvpcConfiguration is required and must list subnets and securityGroups; assignPublicIp (ENABLED/DISABLED, default DISABLED) controls whether the task's ENI gets a public IP.
4. Pin a Fargate platform version with --platform-version (e.g. 1.4.0 or LATEST); if omitted, ECS uses the latest revision of the platform version.
5. Apply per-run overrides with --overrides, e.g. '{"containerOverrides":[{"name":"my-container","command":["python","job.py"],"environment":[{"name":"ENV","value":"prod"}]}]}' to change command/env/cpu/memory without a new task definition revision.
6. Tag the run with --tags key=Job,value=nightly-etl and --propagate-tags TASK_DEFINITION if you want task-definition tags copied onto the task.
7. Capture the task ARN from the RunTask response (tasks[0].taskArn).
8. Block until it finishes: aws ecs wait tasks-stopped --cluster my-cluster --tasks <taskArn> (polls DescribeTasks every 6 seconds, up to 100 attempts, ~10 minutes before failing with exit code 255).
9. Read the outcome: aws ecs describe-tasks --cluster my-cluster --tasks <taskArn> --query 'tasks[0].containers[].{name:name,exitCode:exitCode,reason:reason}' — exitCode 0 means success; a populated reason with a null exitCode usually means the container never started or was killed.
10. Also check tasks[0].stopCode and tasks[0].stoppedReason at the task level for infrastructure-level failures distinct from the container's own exitCode.
11. Official docs: https://docs.aws.amazon.com/AmazonECS/latest/APIReference/API_RunTask.html | https://docs.aws.amazon.com/cli/latest/reference/ecs/wait/tasks-stopped.html | https://docs.aws.amazon.com/AmazonECS/latest/APIReference/API_Container.html | https://docs.aws.amazon.com/AmazonECS/latest/developerguide/task_cannot_pull_image.html