Fix panic draining when alloc on non-existent node

CHANGELOG.md

@@ -8,6 +8,9 @@ IMPROVEMENTS:
  * ui: Stop job button added to job detail pages [[GH-4189](https://github.com/hashicorp/nomad/pull/4189)]
 
 BUG FIXES:
+ * core: Fix panic when doing a node drain effecting a job that has an
+   allocation that was on a node that no longer exists
+   [[GH-4215](https://github.com/hashicorp/nomad/issues/4215)]
  * driver/exec: Create process group for Windows process and send Ctrl-Break signal on Shutdown [[GH-4153](https://github.com/hashicorp/nomad/pull/4153)]
  * ui: Alloc stats will continue to poll after a request errors or returns an invalid response [[GH-4195](https://github.com/hashicorp/nomad/pull/4195)]
 

nomad/drainer/draining_node.go

@@ -125,6 +125,11 @@ func (n *drainingNode) DrainingJobs() ([]structs.NamespacedID, error) {
 	n.l.RLock()
 	defer n.l.RUnlock()
 
+	// Should never happen
+	if n.node == nil || n.node.DrainStrategy == nil {
+		return nil, fmt.Errorf("node doesn't have a drain strategy set")
+	}
+
 	// Retrieve the allocs on the node
 	allocs, err := n.state.AllocsByNode(nil, n.node.ID)
 	if err != nil {

nomad/drainer/watch_jobs.go

@@ -352,8 +352,9 @@ func handleTaskGroup(snap *state.StateSnapshot, batch bool, tg *structs.TaskGrou
 				return err
 			}
 
-			onDrainingNode = node.DrainStrategy != nil
-			drainingNodes[node.ID] = onDrainingNode
+			// Check if the node exists and whether it has a drain strategy
+			onDrainingNode = node != nil && node.DrainStrategy != nil
+			drainingNodes[alloc.NodeID] = onDrainingNode
 		}
 
 		// Check if the alloc should be considered migrated. A migrated

nomad/drainer/watch_jobs_test.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/hashicorp/nomad/helper"
 	"github.com/hashicorp/nomad/helper/testlog"
+	"github.com/hashicorp/nomad/helper/uuid"
 	"github.com/hashicorp/nomad/nomad/mock"
 	"github.com/hashicorp/nomad/nomad/state"
 	"github.com/hashicorp/nomad/nomad/structs"
@@ -663,3 +664,75 @@ func TestHandleTaskGroup_Migrations(t *testing.T) {
 	require.Empty(res.migrated)
 	require.True(res.done)
 }
+
+// This test asserts that handle task group works when an allocation is on a
+// garbage collected node
+func TestHandleTaskGroup_GarbageCollectedNode(t *testing.T) {
+	t.Parallel()
+	require := require.New(t)
+
+	// Create a draining node
+	state := state.TestStateStore(t)
+	n := mock.Node()
+	n.DrainStrategy = &structs.DrainStrategy{
+		DrainSpec: structs.DrainSpec{
+			Deadline: 5 * time.Minute,
+		},
+		ForceDeadline: time.Now().Add(1 * time.Minute),
+	}
+	require.Nil(state.UpsertNode(100, n))
+
+	job := mock.Job()
+	require.Nil(state.UpsertJob(101, job))
+
+	// Create 10 done allocs
+	var allocs []*structs.Allocation
+	for i := 0; i < 10; i++ {
+		a := mock.Alloc()
+		a.Job = job
+		a.TaskGroup = job.TaskGroups[0].Name
+		a.NodeID = n.ID
+		a.DeploymentStatus = &structs.AllocDeploymentStatus{
+			Healthy: helper.BoolToPtr(false),
+		}
+
+		if i%2 == 0 {
+			a.DesiredStatus = structs.AllocDesiredStatusStop
+		} else {
+			a.ClientStatus = structs.AllocClientStatusFailed
+		}
+		allocs = append(allocs, a)
+	}
+
+	// Make the first one be on a GC'd node
+	allocs[0].NodeID = uuid.Generate()
+	require.Nil(state.UpsertAllocs(102, allocs))
+
+	snap, err := state.Snapshot()
+	require.Nil(err)
+
+	// Handle before and after indexes as both service and batch
+	res := newJobResult()
+	require.Nil(handleTaskGroup(snap, false, job.TaskGroups[0], allocs, 101, res))
+	require.Empty(res.drain)
+	require.Len(res.migrated, 9)
+	require.True(res.done)
+
+	res = newJobResult()
+	require.Nil(handleTaskGroup(snap, true, job.TaskGroups[0], allocs, 101, res))
+	require.Empty(res.drain)
+	require.Len(res.migrated, 9)
+	require.True(res.done)
+
+	res = newJobResult()
+	require.Nil(handleTaskGroup(snap, false, job.TaskGroups[0], allocs, 103, res))
+	require.Empty(res.drain)
+	require.Empty(res.migrated)
+	require.True(res.done)
+
+	res = newJobResult()
+	require.Nil(handleTaskGroup(snap, true, job.TaskGroups[0], allocs, 103, res))
+	require.Empty(res.drain)
+	require.Empty(res.migrated)
+	require.True(res.done)
+}

nomad/drainer_int_test.go

@@ -11,6 +11,7 @@ import (
 	memdb "github.com/hashicorp/go-memdb"
 	msgpackrpc "github.com/hashicorp/net-rpc-msgpackrpc"
 	"github.com/hashicorp/nomad/helper"
+	"github.com/hashicorp/nomad/helper/uuid"
 	"github.com/hashicorp/nomad/nomad/mock"
 	"github.com/hashicorp/nomad/nomad/state"
 	"github.com/hashicorp/nomad/nomad/structs"
@@ -658,6 +659,171 @@ func TestDrainer_AllTypes_NoDeadline(t *testing.T) {
 	})
 }
 
+func TestDrainer_AllTypes_Deadline_GarbageCollectedNode(t *testing.T) {
+	t.Parallel()
+	require := require.New(t)
+	s1 := TestServer(t, nil)
+	defer s1.Shutdown()
+	codec := rpcClient(t, s1)
+	testutil.WaitForLeader(t, s1.RPC)
+
+	// Create two nodes, registering the second later
+	n1, n2 := mock.Node(), mock.Node()
+	nodeReg := &structs.NodeRegisterRequest{
+		Node:         n1,
+		WriteRequest: structs.WriteRequest{Region: "global"},
+	}
+	var nodeResp structs.NodeUpdateResponse
+	require.Nil(msgpackrpc.CallWithCodec(codec, "Node.Register", nodeReg, &nodeResp))
+
+	// Create a service job that runs on just one
+	job := mock.Job()
+	job.TaskGroups[0].Count = 2
+	req := &structs.JobRegisterRequest{
+		Job: job,
+		WriteRequest: structs.WriteRequest{
+			Region:    "global",
+			Namespace: job.Namespace,
+		},
+	}
+
+	// Fetch the response
+	var resp structs.JobRegisterResponse
+	require.Nil(msgpackrpc.CallWithCodec(codec, "Job.Register", req, &resp))
+	require.NotZero(resp.Index)
+	job.CreateIndex = resp.JobModifyIndex
+
+	// Create a system job
+	sysjob := mock.SystemJob()
+	req = &structs.JobRegisterRequest{
+		Job: sysjob,
+		WriteRequest: structs.WriteRequest{
+			Region:    "global",
+			Namespace: job.Namespace,
+		},
+	}
+
+	// Fetch the response
+	require.Nil(msgpackrpc.CallWithCodec(codec, "Job.Register", req, &resp))
+	require.NotZero(resp.Index)
+	sysjob.CreateIndex = resp.JobModifyIndex
+
+	// Create a batch job
+	bjob := mock.BatchJob()
+	bjob.TaskGroups[0].Count = 2
+	req = &structs.JobRegisterRequest{
+		Job: bjob,
+		WriteRequest: structs.WriteRequest{
+			Region:    "global",
+			Namespace: job.Namespace,
+		},
+	}
+
+	// Fetch the response
+	require.Nil(msgpackrpc.CallWithCodec(codec, "Job.Register", req, &resp))
+	require.NotZero(resp.Index)
+	bjob.CreateIndex = resp.JobModifyIndex
+
+	// Wait for the allocations to be placed
+	state := s1.State()
+	testutil.WaitForResult(func() (bool, error) {
+		allocs, err := state.AllocsByNode(nil, n1.ID)
+		if err != nil {
+			return false, err
+		}
+		return len(allocs) == 5, fmt.Errorf("got %d allocs", len(allocs))
+	}, func(err error) {
+		t.Fatalf("err: %v", err)
+	})
+
+	// Create some old terminal allocs for each job that point at a non-existent
+	// node to simulate it being on a GC'd node.
+	var badAllocs []*structs.Allocation
+	for _, job := range []*structs.Job{job, sysjob, bjob} {
+		alloc := mock.Alloc()
+		alloc.Namespace = job.Namespace
+		alloc.Job = job
+		alloc.JobID = job.ID
+		alloc.NodeID = uuid.Generate()
+		alloc.TaskGroup = job.TaskGroups[0].Name
+		alloc.DesiredStatus = structs.AllocDesiredStatusStop
+		alloc.ClientStatus = structs.AllocClientStatusComplete
+		badAllocs = append(badAllocs, alloc)
+	}
+	require.NoError(state.UpsertAllocs(1, badAllocs))
+
+	// Create the second node
+	nodeReg = &structs.NodeRegisterRequest{
+		Node:         n2,
+		WriteRequest: structs.WriteRequest{Region: "global"},
+	}
+	require.Nil(msgpackrpc.CallWithCodec(codec, "Node.Register", nodeReg, &nodeResp))
+
+	// Drain the node
+	drainReq := &structs.NodeUpdateDrainRequest{
+		NodeID: n1.ID,
+		DrainStrategy: &structs.DrainStrategy{
+			DrainSpec: structs.DrainSpec{
+				Deadline: 2 * time.Second,
+			},
+		},
+		WriteRequest: structs.WriteRequest{Region: "global"},
+	}
+	var drainResp structs.NodeDrainUpdateResponse
+	require.Nil(msgpackrpc.CallWithCodec(codec, "Node.UpdateDrain", drainReq, &drainResp))
+
+	// Wait for the allocs to be replaced
+	errCh := make(chan error, 2)
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	go allocPromoter(errCh, ctx, state, codec, n1.ID, s1.logger)
+	go allocPromoter(errCh, ctx, state, codec, n2.ID, s1.logger)
+
+	// Wait for the allocs to be stopped
+	var finalAllocs []*structs.Allocation
+	testutil.WaitForResult(func() (bool, error) {
+		if err := checkAllocPromoter(errCh); err != nil {
+			return false, err
+		}
+
+		var err error
+		finalAllocs, err = state.AllocsByNode(nil, n1.ID)
+		if err != nil {
+			return false, err
+		}
+		for _, alloc := range finalAllocs {
+			if alloc.DesiredStatus != structs.AllocDesiredStatusStop {
+				return false, fmt.Errorf("got desired status %v", alloc.DesiredStatus)
+			}
+		}
+		return true, nil
+	}, func(err error) {
+		t.Fatalf("err: %v", err)
+	})
+
+	// Check that the node drain is removed
+	testutil.WaitForResult(func() (bool, error) {
+		node, err := state.NodeByID(nil, n1.ID)
+		if err != nil {
+			return false, err
+		}
+		return node.DrainStrategy == nil, fmt.Errorf("has drain strategy still set")
+	}, func(err error) {
+		t.Fatalf("err: %v", err)
+	})
+
+	// Wait for the allocations to be placed on the other node
+	testutil.WaitForResult(func() (bool, error) {
+		allocs, err := state.AllocsByNode(nil, n2.ID)
+		if err != nil {
+			return false, err
+		}
+		return len(allocs) == 5, fmt.Errorf("got %d allocs", len(allocs))
+	}, func(err error) {
+		t.Fatalf("err: %v", err)
+	})
+}
+
 // Test that transistions to force drain work.
 func TestDrainer_Batch_TransitionToForce(t *testing.T) {
 	t.Parallel()