Route ECS container stdout/stderr to CloudWatch Logs with the awslogs driver, then tail, filter, and set retention on those logs

Documented steps

1. In the container definition set logConfiguration: {"logDriver": "awslogs", "options": {"awslogs-group": "/ecs/my-app", "awslogs-region": "us-east-1", "awslogs-stream-prefix": "my-app"}}
2. awslogs-stream-prefix is REQUIRED for Fargate launch type (optional on EC2, where streams fall back to the Docker container ID) and is required for logs to appear in the ECS console Logs tab.
3. Either pre-create the log group (aws logs create-log-group --log-group-name /ecs/my-app) or set "awslogs-create-group": "true" in options.
4. Grant the task EXECUTION role logs:CreateLogStream and logs:PutLogEvents on the log group ARN, plus logs:CreateLogGroup if awslogs-create-group is true. On EC2, the container instance role also needs these and the agent needs ECS_AVAILABLE_LOGGING_DRIVERS=["json-file","awslogs"] (agent 1.9.0+).
5. Register the task definition: aws ecs register-task-definition --cli-input-json file://taskdef.json, then run or update the service.
6. Log streams are named prefix-name/container-name/ecs-task-id, e.g. my-app/web/1abf0f6d-a703-4448-9c51-e2b8f6f8f793 — use this to locate a specific task's logs.
7. Tail in near-real-time: aws logs tail /ecs/my-app --since 30m --follow, optionally with --filter-pattern "ERROR".
8. Search a historical window: aws logs filter-log-events --log-group-name /ecs/my-app --filter-pattern "ERROR" --start-time $(date -d '-1 hour' +%s000)
9. Set retention (default is Never Expire, i.e. indefinite storage and cost): aws logs put-retention-policy --log-group-name /ecs/my-app --retention-in-days 30
10. Optionally tune delivery with the mode (blocking|non-blocking) and max-buffer-size (default 10m) options to trade log-loss against application backpressure under burst load.
11. Official docs: https://docs.aws.amazon.com/AmazonECS/latest/developerguide/specify-log-config.html | https://docs.aws.amazon.com/AmazonECS/latest/APIReference/API_LogConfiguration.html | https://docs.aws.amazon.com/cli/latest/reference/logs/tail.html | https://docs.aws.amazon.com/AmazonCloudWatch/latest/logs/Working-with-log-groups-and-streams.html