scheduler: fix panic when preempting and evicting allocs

CHANGELOG.md

@@ -26,6 +26,7 @@ BUG FIXES:
 
  * core: Ignore `server` config values if `server` is disabled [[GH-6047](https://github.com/hashicorp/nomad/issues/6047)]
  * core: Added `semver` constraint for strict Semver 2.0 version comparisons [[GH-6699](https://github.com/hashicorp/nomad/issues/6699)]
+ * core: Fixed server panic caused by a plan evicting and preempting allocs on a node [[GH-6792](https://github.com/hashicorp/nomad/issues/6792)]
  * api: Return a 404 if endpoint not found instead of redirecting to /ui/ [[GH-6658](https://github.com/hashicorp/nomad/issues/6658)]
  * api: Decompress web socket response body if gzipped on error responses [[GH-6650](https://github.com/hashicorp/nomad/issues/6650)]
  * api: Fixed a bug where some FS/Allocation API endpoints didn't return error messages [[GH-6427](https://github.com/hashicorp/nomad/issues/6427)]

scheduler/context.go

@@ -25,9 +25,9 @@ type Context interface {
 	// Reset is invoked after making a placement
 	Reset()
 
-	// ProposedAllocs returns the proposed allocations for a node
-	// which is the existing allocations, removing evictions, and
-	// adding any planned placements.
+	// ProposedAllocs returns the proposed allocations for a node which are
+	// the existing allocations, removing evictions, and adding any planned
+	// placements.
 	ProposedAllocs(nodeID string) ([]*structs.Allocation, error)
 
 	// RegexpCache is a cache of regular expressions
@@ -120,22 +120,21 @@ func (e *EvalContext) Reset() {
 func (e *EvalContext) ProposedAllocs(nodeID string) ([]*structs.Allocation, error) {
 	// Get the existing allocations that are non-terminal
 	ws := memdb.NewWatchSet()
-	existingAlloc, err := e.state.AllocsByNodeTerminal(ws, nodeID, false)
+	proposed, err := e.state.AllocsByNodeTerminal(ws, nodeID, false)
 	if err != nil {
 		return nil, err
 	}
 
 	// Determine the proposed allocation by first removing allocations
 	// that are planned evictions and adding the new allocations.
-	proposed := existingAlloc
 	if update := e.plan.NodeUpdate[nodeID]; len(update) > 0 {
-		proposed = structs.RemoveAllocs(existingAlloc, update)
+		proposed = structs.RemoveAllocs(proposed, update)
 	}
 
 	// Remove any allocs that are being preempted
 	nodePreemptedAllocs := e.plan.NodePreemptions[nodeID]
 	if len(nodePreemptedAllocs) > 0 {
-		proposed = structs.RemoveAllocs(existingAlloc, nodePreemptedAllocs)
+		proposed = structs.RemoveAllocs(proposed, nodePreemptedAllocs)
 	}
 
 	// We create an index of the existing allocations so that if an inplace

scheduler/context_test.go

@@ -106,9 +106,9 @@ func TestEvalContext_ProposedAlloc(t *testing.T) {
 		ClientStatus:  structs.AllocClientStatusPending,
 		TaskGroup:     "web",
 	}
-	noErr(t, state.UpsertJobSummary(998, mock.JobSummary(alloc1.JobID)))
-	noErr(t, state.UpsertJobSummary(999, mock.JobSummary(alloc2.JobID)))
-	noErr(t, state.UpsertAllocs(1000, []*structs.Allocation{alloc1, alloc2}))
+	require.NoError(t, state.UpsertJobSummary(998, mock.JobSummary(alloc1.JobID)))
+	require.NoError(t, state.UpsertJobSummary(999, mock.JobSummary(alloc2.JobID)))
+	require.NoError(t, state.UpsertAllocs(1000, []*structs.Allocation{alloc1, alloc2}))
 
 	// Add a planned eviction to alloc1
 	plan := ctx.Plan()
@@ -149,6 +149,116 @@ func TestEvalContext_ProposedAlloc(t *testing.T) {
 	}
 }
 
+// TestEvalContext_ProposedAlloc_EvictPreempt asserts both Evicted and
+// Preempted allocs are removed from the allocs propsed for a node.
+//
+// See https://github.com/hashicorp/nomad/issues/6787
+//
+func TestEvalContext_ProposedAlloc_EvictPreempt(t *testing.T) {
+	t.Parallel()
+	state, ctx := testContext(t)
+	nodes := []*RankedNode{
+		{
+			Node: &structs.Node{
+				ID: uuid.Generate(),
+				NodeResources: &structs.NodeResources{
+					Cpu: structs.NodeCpuResources{
+						CpuShares: 1024 * 3,
+					},
+					Memory: structs.NodeMemoryResources{
+						MemoryMB: 1024 * 3,
+					},
+				},
+			},
+		},
+	}
+
+	// Add existing allocations
+	j1, j2, j3 := mock.Job(), mock.Job(), mock.Job()
+	allocEvict := &structs.Allocation{
+		ID:        uuid.Generate(),
+		Namespace: structs.DefaultNamespace,
+		EvalID:    uuid.Generate(),
+		NodeID:    nodes[0].Node.ID,
+		JobID:     j1.ID,
+		Job:       j1,
+		AllocatedResources: &structs.AllocatedResources{
+			Tasks: map[string]*structs.AllocatedTaskResources{
+				"web": {
+					Cpu: structs.AllocatedCpuResources{
+						CpuShares: 1024,
+					},
+					Memory: structs.AllocatedMemoryResources{
+						MemoryMB: 1024,
+					},
+				},
+			},
+		},
+		DesiredStatus: structs.AllocDesiredStatusRun,
+		ClientStatus:  structs.AllocClientStatusPending,
+		TaskGroup:     "web",
+	}
+	allocPreempt := &structs.Allocation{
+		ID:        uuid.Generate(),
+		Namespace: structs.DefaultNamespace,
+		EvalID:    uuid.Generate(),
+		NodeID:    nodes[0].Node.ID,
+		JobID:     j2.ID,
+		Job:       j2,
+		AllocatedResources: &structs.AllocatedResources{
+			Tasks: map[string]*structs.AllocatedTaskResources{
+				"web": {
+					Cpu: structs.AllocatedCpuResources{
+						CpuShares: 1024,
+					},
+					Memory: structs.AllocatedMemoryResources{
+						MemoryMB: 1024,
+					},
+				},
+			},
+		},
+		DesiredStatus: structs.AllocDesiredStatusRun,
+		ClientStatus:  structs.AllocClientStatusPending,
+		TaskGroup:     "web",
+	}
+	allocPropose := &structs.Allocation{
+		ID:        uuid.Generate(),
+		Namespace: structs.DefaultNamespace,
+		EvalID:    uuid.Generate(),
+		NodeID:    nodes[0].Node.ID,
+		JobID:     j3.ID,
+		Job:       j3,
+		AllocatedResources: &structs.AllocatedResources{
+			Tasks: map[string]*structs.AllocatedTaskResources{
+				"web": {
+					Cpu: structs.AllocatedCpuResources{
+						CpuShares: 1024,
+					},
+					Memory: structs.AllocatedMemoryResources{
+						MemoryMB: 1024,
+					},
+				},
+			},
+		},
+		DesiredStatus: structs.AllocDesiredStatusRun,
+		ClientStatus:  structs.AllocClientStatusPending,
+		TaskGroup:     "web",
+	}
+	require.NoError(t, state.UpsertJobSummary(998, mock.JobSummary(allocEvict.JobID)))
+	require.NoError(t, state.UpsertJobSummary(999, mock.JobSummary(allocPreempt.JobID)))
+	require.NoError(t, state.UpsertJobSummary(999, mock.JobSummary(allocPropose.JobID)))
+	require.NoError(t, state.UpsertAllocs(1000, []*structs.Allocation{allocEvict, allocPreempt, allocPropose}))
+
+	// Plan to evict one alloc and preempt another
+	plan := ctx.Plan()
+	plan.NodePreemptions[nodes[0].Node.ID] = []*structs.Allocation{allocEvict}
+	plan.NodeUpdate[nodes[0].Node.ID] = []*structs.Allocation{allocPreempt}
+
+	proposed, err := ctx.ProposedAllocs(nodes[0].Node.ID)
+	require.NoError(t, err)
+	require.Len(t, proposed, 1)
+}
+
 func TestEvalEligibility_JobStatus(t *testing.T) {
 	e := NewEvalEligibility()
 	cc := "v1:100"