migrate

type InPlaceSpec struct {
	Source isolation.Backend
	// SourceRoot names the slot the source runs in.
	SourceRoot isolation.SlotRef
	Target     isolation.Backend
	// TargetSpec names the alternate slot and the node to prepare.
	TargetSpec isolation.NodeSpec

	// Preflight checks the target backend's requirements before anything is
	// mutated.
	Preflight func(ctx context.Context, target isolation.Backend) error
	// Download fetches the artifacts the target needs. Optional.
	Download func(ctx context.Context) error
	// SnapshotConfig saves the host configuration files both stacks write, before
	// the first step that changes the host. Optional; when set, RestoreConfig
	// should be too. A failure ends the migration with nothing changed.
	SnapshotConfig func(ctx context.Context) error
	// RestoreConfig puts the saved files back during a rollback, after the target
	// is gone and before the source starts. It reports nil when there is no
	// snapshot to restore. The snapshot is kept when it fails.
	RestoreConfig func(ctx context.Context) error
	// DiscardConfig removes the snapshot once the migration is over, after a
	// success or a completed rollback.
	DiscardConfig func(ctx context.Context) error
	// CleanupNetwork removes host networking the source left behind, as a
	// repave does.
	CleanupNetwork func(ctx context.Context) error
	// PersistTarget records the new mode, slot and owning backend.
	PersistTarget func(ctx context.Context, target isolation.SlotRef) error
	// RestoreSource puts the source's applied config back after PersistTarget
	// when the migration rolls back. Required whenever PersistTarget is set.
	RestoreSource func(ctx context.Context) error
	// WaitReady blocks until the target node stack is up on the host or a
	// bounded timeout passes. Cordoning, draining and uncordoning the Node
	// belong to the operator, not to the migration.
	WaitReady func(ctx context.Context) error
	// RemoveSourceConfig removes the source's applied config after success.
	RemoveSourceConfig func(ctx context.Context) error
	// PrepareHost applies the host preparation a bootstrap in the target mode
	// would have, once the target is up: the mode's boot-time firewall flush
	// unit and package-manager guards. Optional. Like the source cleanup, a
	// failure does not undo the migration; it leaves the migration short of
	// StepComplete, so a resume runs it again.
	PrepareHost func(ctx context.Context) error

	// Record, when set, is called before each step that changes the host, with
	// the step about to run (and with StepReady and StepComplete after the
	// matching work). It is a write-ahead log: when Record returns an error the
	// step does not run and the migration is rolled back like any failure.
	// Recording is what lets ResumeInPlace decide what to do after a crash.
	Record func(ctx context.Context, step Step) error
	// TargetRoot names the target slot. Required by ResumeInPlace, which has no
	// Prepare result to take it from; RunInPlace uses it only to clean up after
	// a failed Prepare.
	TargetRoot isolation.SlotRef
}

type Journal struct {
	Version  int            `json:"version"`
	Strategy Strategy       `json:"strategy"`
	From     isolation.Mode `json:"from"`
	To       isolation.Mode `json:"to"`
	// SourceSlot and TargetSlot are the blue/green slots of an in-place
	// migration. Reprovision leaves them empty.
	SourceSlot string    `json:"sourceSlot,omitempty"`
	TargetSlot string    `json:"targetSlot,omitempty"`
	Step       Step      `json:"step"`
	StartedAt  time.Time `json:"startedAt"`
	UpdatedAt  time.Time `json:"updatedAt"`
	// Attempts counts the runs of a reprovision handoff that started, so the
	// handoff can give up after a bounded number of them.
	Attempts int `json:"attempts,omitempty"`
	// Message is the last failure the handoff command saw, for operators.
	Message string `json:"message,omitempty"`
}

type JournalStore struct {
	Path string
	// Now overrides the clock. Nil means time.Now.
	Now func() time.Time
}

type Result struct {
	// Target is the slot the node now runs in. Nil unless the migration
	// succeeded.
	Target isolation.SlotRef
	// RolledBack is true when a failure was followed by a restart of the source.
	RolledBack bool
}

type Step string

type Strategy string