Service and Task

Definitions

Swarm-mode primitives:

• Service — the desired-state spec for an N-replica workload (image, env, mounts, networks, update policy).
• Task — a single instance of a service assigned to a node.

These types come from SwarmKit and are surfaced through the Engine API in api/types/swarm/.

Wire types

Type	File	Purpose
Service	api/types/swarm/service.go	A swarm service.
Task	api/types/swarm/task.go	A scheduled instance.
Node	api/types/swarm/node.go	A swarm node.
Secret	api/types/swarm/secret.go	Encrypted secret payload.
Config	api/types/swarm/config.go	Plain-text configuration payload.
Swarm	api/types/swarm/swarm.go	Cluster-wide config (orchestration, raft, ...).
RuntimeContainerSpec, Networking, Endpoint, UpdateConfig, RestartPolicy, ...	Sub-objects

Conversion

API types ↔ SwarmKit protobufs in daemon/cluster/convert/. Each resource has a service.go, task.go, etc. with From* and To* functions.

Lifecycle

graph LR
  Service[Service spec] -->|orchestrator| TaskSpec[Task spec]
  TaskSpec -->|scheduler| Assignment[Node assignment]
  Assignment -->|agent on node| Executor[daemon/cluster/executor]
  Executor --> Container[local container]
  Container -->|state| Agent
  Agent -->|reports| Manager

The orchestrator and scheduler run only on manager nodes. The agent runs on every node and uses Moby's executor to launch tasks as local containers via the container runtime.

Service-level networking

Each service can attach to one or more cluster-scoped networks. The libnetwork controller exposes service VIPs and DNSRR via its embedded resolver. See Networking (libnetwork) and Swarm cluster.

Secrets & configs

Swarm secrets and configs are key-value payloads stored in the manager's Raft DB and mounted into tasks at /run/secrets/<name> (secrets) or arbitrary container paths (configs). They're scoped per-service.

See also

• Swarm cluster for the runtime and orchestrator.
• Container — what a task ultimately becomes on a node.