What is the difference between Docker Swarm services and Docker Compose services?

Despite sharing similar YAML syntax, Docker Swarm services and Docker Compose services are different concepts operating at different scales. Docker Compose services: define containers running on a single host; used for local development and single-machine deployments; managed by the Compose CLI (docker compose); containers are not replicated across hosts; restart is local only; depends_on controls startup order; typically no placement constraints. Docker Swarm services: define tasks distributed across a multi-node cluster; multiple replicas run across multiple machines; the Swarm manager schedules and balances; provide built-in load balancing (Swarm's routing mesh distributes requests across replicas on any node); rolling updates with configurable parallelism and delay; placement constraints (node.role == worker, node.labels.environment == production); resource reservations and limits for scheduling; global mode (one replica per node) or replicated mode. Swarm uses the same Compose YAML syntax but with additional fields under deploy:: deploy: replicas: 3 update_config: parallelism: 1 delay: 10s rollback_config: ... placement: constraints: [node.role == worker] resources: limits: cpus: "0.5" memory: 512M. Deploy a stack to Swarm: docker stack deploy -c docker-compose.yml mystack.