Fix in-place updates over ineligible nodes

.changelog/12264.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+scheduler: fixed a bug where in-place updates on ineligible nodes would be ignored
+```

nomad/plan_apply.go

@@ -662,8 +662,6 @@ func evaluateNodePlan(snap *state.StateSnapshot, plan *structs.Plan, nodeID stri
 		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 {
-		return false, "node is not eligible", nil
 	}
 
 	// Get the existing allocations that are non-terminal
@@ -672,6 +670,15 @@ func evaluateNodePlan(snap *state.StateSnapshot, plan *structs.Plan, nodeID stri
 		return false, "", fmt.Errorf("failed to get existing allocations for '%s': %v", nodeID, err)
 	}
 
+	// If nodeAllocations is a subset of the existing allocations we can continue,
+	// even if the node is not eligible, as only in-place updates or stop/evict are performed
+	if structs.AllocSubset(existingAlloc, plan.NodeAllocation[nodeID]) {
+		return true, "", nil
+	}
+	if node.SchedulingEligibility == structs.NodeSchedulingIneligible {
+		return false, "node is not eligible", nil
+	}
+
 	// Determine the proposed allocation by first removing allocations
 	// that are planned evictions and adding the new allocations.
 	var remove []*structs.Allocation

nomad/plan_apply_test.go

@@ -887,6 +887,39 @@ func TestPlanApply_EvalNodePlan_UpdateExisting(t *testing.T) {
 	}
 }
 
+func TestPlanApply_EvalNodePlan_UpdateExisting_Ineligible(t *testing.T) {
+	t.Parallel()
+	alloc := mock.Alloc()
+	state := testStateStore(t)
+	node := mock.Node()
+	node.ReservedResources = nil
+	node.Reserved = nil
+	node.SchedulingEligibility = structs.NodeSchedulingIneligible
+	alloc.NodeID = node.ID
+	alloc.AllocatedResources = structs.NodeResourcesToAllocatedResources(node.NodeResources)
+	state.UpsertNode(structs.MsgTypeTestSetup, 1000, node)
+	state.UpsertAllocs(structs.MsgTypeTestSetup, 1001, []*structs.Allocation{alloc})
+	snap, _ := state.Snapshot()
+
+	plan := &structs.Plan{
+		Job: alloc.Job,
+		NodeAllocation: map[string][]*structs.Allocation{
+			node.ID: {alloc},
+		},
+	}
+
+	fit, reason, err := evaluateNodePlan(snap, plan, node.ID)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	if !fit {
+		t.Fatalf("bad")
+	}
+	if reason != "" {
+		t.Fatalf("bad")
+	}
+}
+
 func TestPlanApply_EvalNodePlan_NodeFull_Evict(t *testing.T) {
 	ci.Parallel(t)
 	alloc := mock.Alloc()

nomad/structs/funcs.go

@@ -64,6 +64,24 @@ func RemoveAllocs(allocs []*Allocation, remove []*Allocation) []*Allocation {
 	return r
 }
 
+func AllocSubset(allocs []*Allocation, subset []*Allocation) bool {
+	if len(subset) == 0 {
+		return true
+	}
+	// Convert allocs into a map
+	allocMap := make(map[string]struct{})
+	for _, alloc := range allocs {
+		allocMap[alloc.ID] = struct{}{}
+	}
+
+	for _, alloc := range subset {
+		if _, ok := allocMap[alloc.ID]; !ok {
+			return false
+		}
+	}
+	return true
+}
+
 // FilterTerminalAllocs filters out all allocations in a terminal state and
 // returns the latest terminal allocations.
 func FilterTerminalAllocs(allocs []*Allocation) ([]*Allocation, map[string]*Allocation) {