cluster

type Disk struct {
	// ID identifies the disk within its node.
	ID DiskID
	// Weight is the relative capacity weight used by weighted placement. A disk
	// with weight <= 0 is drained: it is never chosen for new placement (used
	// when decommissioning or when a disk is full/faulted).
	Weight float64
	// TotalBytes/FreeBytes are the disk's reported filesystem capacity,
	// refreshed by its node's registration; 0/0 means unknown. Observability
	// input only — placement uses Weight, and Signature ignores capacity so
	// usage churn never reads as a membership change.
	TotalBytes uint64
	FreeBytes  uint64
}

type DiskID string

type Node struct {
	// ID identifies the node.
	ID NodeID
	// Addr is the node's cluster-listener address (host:port). Placement does
	// not use it; it is carried for the caller that dispatches to targets.
	Addr string
	// Rack is the failure-domain label. Nodes sharing a rack share fate (power,
	// switch); an empty rack means "unknown", treated as its own single domain
	// keyed by node so such nodes never falsely appear rack-diverse.
	Rack string
	// Disks are the node's storage devices.
	Disks []Disk
}

type NodeID string

type Topology struct {
	// Epoch is the monotonically increasing version of this snapshot (the etcd
	// revision it was derived from). Placement output is stable within an epoch.
	Epoch uint64
	// Nodes are the members. Order is not significant to placement.
	Nodes []Node
}