Systems

The daemon is divided into roughly a dozen internal subsystems that the central Daemon struct stitches together. This section has one page per major subsystem, ordered from most-touched to most-specialized.

Subsystem	Code	What it does
Daemon core	daemon/	The god-object that wires everything together, plus container lifecycle.
API server	daemon/server/	HTTP server, routers, middlewares, error mapping.
Container runtime	daemon/internal/libcontainerd/	Bridge to containerd for low-level container lifecycle.
Image management	daemon/containerd/, daemon/internal/image/	Two image services (containerd-backed and legacy) behind a common interface.
Distribution	daemon/internal/distribution/	Registry pull/push for the legacy image store.
Builder	daemon/builder/, daemon/internal/builder-next/	Classic Dockerfile builder + BuildKit integration.
Networking (libnetwork)	daemon/libnetwork/	CNM controller, drivers (bridge/overlay/macvlan/ipvlan/host/null), DNS, port allocation.
Volumes	daemon/volume/	Volumes service, local driver, mount management.
Logging	daemon/logger/	Container log driver registry and built-in drivers.
Graphdrivers	daemon/graphdriver/	Legacy union-FS drivers (overlay2, vfs, btrfs, zfs, fuse-overlayfs, windows).
Swarm cluster	daemon/cluster/	Embedded SwarmKit-based clustering.
Plugins	daemon/pkg/plugin/, pkg/plugins/	Managed (v2) and legacy (v1) plugin systems.
Events	daemon/events/	Pub/sub event bus published over the API.

These subsystems are intentionally coupled through small interfaces. The big architectural goal in ROADMAP.md is to keep splitting Daemon into smaller pieces and to push more lifecycle work down into containerd.