Docker Compose Support

If your repo contains a docker-compose.yml (or docker-compose.yaml), setup parses it (src/utils/dockerCompose.js) and translates its services into the ECS task definition. Your Compose file keeps working locally, and these are the exact mapping rules that decide what runs in AWS.

File discovery

Only the repo root is checked, trying docker-compose.yml first and then docker-compose.yaml. A file with no services key — or one that fails YAML parsing — is treated as absent (a warning is printed, setup continues), so a stray or malformed file never blocks generation.

Which service is “web”

The service used as the ECS web service is the first service with an exposed port; if none exposes a port, the first service listed wins. Every other service becomes an ECS sidecar in the same task definition. Structure your file accordingly: the publicly reachable app must be the port-exposing service.

Port mapping

The container port is taken from the last segment of the first port entry — "8080:80" and "127.0.0.1:8001:8001" both resolve to the right-hand value (80 and 8001). Only the first entry is read, and any non-numeric characters are stripped. This port overrides the configured container port during setup, and the ALB health check targets it.

Environment and command injection

Environment supports both Compose styles: environment: as a mapping is used as-is; as a list (- KEY=value) each entry is split on the first =.
The web service’s variables are injected directly into the ECS task definition, and its command overrides the container start command — but only when no Procfile web: process already set one (Procfile wins; see Dockerfiles).
Sidecars get the same treatment: their environment is injected, their command is preserved, a missing image defaults to alpine:latest, and each sidecar logs to the shared CloudWatch log group under an ecs-<service> stream prefix.

What this means in practice

Sidecars (Redis, Memcached, background helpers) run in the same task as the web container and share its lifecycle — this is co-location, not separate services.
Compose build: contexts are not used in AWS; the image is built from the generated Dockerfile by the CI/CD pipeline.
Runtime secrets still belong in AWS Secrets Manager, not in Compose environment:. See Secrets Management.