evaluateNodePlan: validate plans for disconnected nodes

nomad/plan_apply.go

@@ -655,6 +655,11 @@ func evaluateNodePlan(snap *state.StateSnapshot, plan *structs.Plan, nodeID stri
 	// the Raft commit happens.
 	if node == nil {
 		return false, "node does not exist", nil
+	} else if node.Status == structs.NodeStatusDisconnected {
+		if isValidForDisconnectedNode(plan, node.ID) {
+			return true, "", nil
+		}
+		return false, "node is disconnected and contains invalid updates", nil
 	} else if node.Status != structs.NodeStatusReady {
 		return false, "node is not ready for placements", nil
 	} else if node.SchedulingEligibility == structs.NodeSchedulingIneligible {
@@ -690,6 +695,22 @@ func evaluateNodePlan(snap *state.StateSnapshot, plan *structs.Plan, nodeID stri
 	return fit, reason, err
 }
 
+// The plan is only valid for disconnected nodes if it only contains
+// updates to mark allocations as unknown.
+func isValidForDisconnectedNode(plan *structs.Plan, nodeID string) bool {
+	if len(plan.NodeUpdate[nodeID]) != 0 || len(plan.NodePreemptions[nodeID]) != 0 {
+		return false
+	}
+
+	for _, alloc := range plan.NodeAllocation[nodeID] {
+		if alloc.ClientStatus != structs.AllocClientStatusUnknown {
+			return false
+		}
+	}
+
+	return true
+}
+
 func max(a, b uint64) uint64 {
 	if a > b {
 		return a