dynamic host volumes: account for other claims in capability check

When we feasibility check a dynamic host volume against a volume request, we
check the attachment mode and access mode. This only ensures that the
capabilities match, but doesn't enforce the semantics of the capabilities
against other claims that may be made on the allocation.

Add support for checking the requested capability against other allocations that
the volume claimed.

Requires additional updates:
* Job validation should allow attachment/access mode for host volumes
* Added new single-node access modes and removed multi-node access modes

Ref: #24479

nomad/state/state_store_host_volumes.go

@@ -30,6 +30,7 @@ func (s *StateStore) HostVolumeByID(ws memdb.WatchSet, ns, id string, withAllocs
 
 	vol = vol.Copy()
 	vol.Allocations = []*structs.AllocListStub{}
+	vol.Writers = []string{}
 
 	// we can't use AllocsByNodeTerminal because we only want to filter out
 	// allocs that are client-terminal, not server-terminal
@@ -43,6 +44,9 @@ func (s *StateStore) HostVolumeByID(ws memdb.WatchSet, ns, id string, withAllocs
 		}
 		for _, volClaim := range alloc.Job.LookupTaskGroup(alloc.TaskGroup).Volumes {
 			if volClaim.Type == structs.VolumeTypeHost && volClaim.Source == vol.Name {
+				if !volClaim.ReadOnly {
+					vol.Writers = append(vol.Writers, alloc.ID)
+				}
 				vol.Allocations = append(vol.Allocations, alloc.Stub(nil))
 			}
 		}
@@ -101,6 +105,7 @@ func (s *StateStore) UpsertHostVolume(index uint64, vol *structs.HostVolume) err
 	// Allocations are denormalized on read, so we don't want these to be
 	// written to the state store.
 	vol.Allocations = nil
+	vol.Writers = nil
 	vol.ModifyIndex = index
 
 	err = txn.Insert(TableHostVolumes, vol)

nomad/structs/host_volumes.go

@@ -84,6 +84,11 @@ type HostVolume struct {
 	// this host volume. They are denormalized on read and this field will be
 	// never written to Raft
 	Allocations []*AllocListStub `json:",omitempty"`
+
+	// Writers and is a list of alloc IDs from the Allocations field that can
+	// write to this volume. This count is denormalized on read, never written
+	// to Raft, and never returned by the API.
+	Writers []string `json:"-"`
 }
 
 type HostVolumeState string
@@ -245,6 +250,47 @@ func (hv *HostVolume) GetID() string {
 	return hv.ID
 }
 
+// IsAvailable determines if the volume is available for a request
+func (hv *HostVolume) IsAvailable(reqAccess HostVolumeAccessMode, reqAttach HostVolumeAttachmentMode, readOnly bool, previousAllocID string) bool {
+
+	if hv.State != HostVolumeStateReady {
+		return false
+	}
+
+	// check that the volume has the requested capability at all
+	var capOk bool
+	for _, cap := range hv.RequestedCapabilities {
+		if reqAccess == cap.AccessMode &&
+			reqAttach == cap.AttachmentMode {
+			capOk = true
+			break
+		}
+	}
+	if !capOk {
+		return false
+	}
+
+	// if no other allocations claim the volume, it's first-come-first-serve to
+	// determine how subsequent allocs can claim it
+	if len(hv.Allocations) == 0 {
+		return true
+	}
+
+	switch reqAccess {
+	case HostVolumeAccessModeUnknown:
+		return false // invalid mode
+	case HostVolumeAccessModeSingleNodeReader:
+		return readOnly
+	case HostVolumeAccessModeSingleNodeWriter, HostVolumeAccessModeSingleNodeSingleWriter:
+		return len(hv.Writers) == 0 ||
+			(len(hv.Writers) == 1 && hv.Writers[0] == previousAllocID)
+	case HostVolumeAccessModeSingleNodeMultiWriter:
+		// no contraint
+	}
+
+	return true
+}
+
 // HostVolumeCapability is the requested attachment and access mode for a volume
 type HostVolumeCapability struct {
 	AttachmentMode HostVolumeAttachmentMode
@@ -275,9 +321,8 @@ func (hvc *HostVolumeCapability) Validate() error {
 	switch hvc.AccessMode {
 	case HostVolumeAccessModeSingleNodeReader,
 		HostVolumeAccessModeSingleNodeWriter,
-		HostVolumeAccessModeMultiNodeReader,
-		HostVolumeAccessModeMultiNodeSingleWriter,
-		HostVolumeAccessModeMultiNodeMultiWriter:
+		HostVolumeAccessModeSingleNodeSingleWriter,
+		HostVolumeAccessModeSingleNodeMultiWriter:
 	default:
 		return fmt.Errorf("invalid access mode: %q", hvc.AccessMode)
 	}
@@ -302,12 +347,10 @@ type HostVolumeAccessMode string
 const (
 	HostVolumeAccessModeUnknown HostVolumeAccessMode = ""
 
-	HostVolumeAccessModeSingleNodeReader HostVolumeAccessMode = "single-node-reader-only"
-	HostVolumeAccessModeSingleNodeWriter HostVolumeAccessMode = "single-node-writer"
-
-	HostVolumeAccessModeMultiNodeReader       HostVolumeAccessMode = "multi-node-reader-only"
-	HostVolumeAccessModeMultiNodeSingleWriter HostVolumeAccessMode = "multi-node-single-writer"
-	HostVolumeAccessModeMultiNodeMultiWriter  HostVolumeAccessMode = "multi-node-multi-writer"
+	HostVolumeAccessModeSingleNodeReader       HostVolumeAccessMode = "single-node-reader-only"
+	HostVolumeAccessModeSingleNodeWriter       HostVolumeAccessMode = "single-node-writer"
+	HostVolumeAccessModeSingleNodeSingleWriter HostVolumeAccessMode = "single-node-single-writer"
+	HostVolumeAccessModeSingleNodeMultiWriter  HostVolumeAccessMode = "single-node-multi-writer"
 )
 
 // HostVolumeStub is used for responses for the list volumes endpoint

nomad/structs/host_volumes_test.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"github.com/hashicorp/nomad/ci"
+	"github.com/hashicorp/nomad/helper"
 	"github.com/hashicorp/nomad/helper/uuid"
 	"github.com/shoenig/test/must"
 )
@@ -45,7 +46,7 @@ func TestHostVolume_Copy(t *testing.T) {
 	out.Constraints[0].LTarget = "${meta.node_class}"
 	out.RequestedCapabilities = append(out.RequestedCapabilities, &HostVolumeCapability{
 		AttachmentMode: HostVolumeAttachmentModeBlockDevice,
-		AccessMode:     HostVolumeAccessModeMultiNodeReader,
+		AccessMode:     HostVolumeAccessModeSingleNodeMultiWriter,
 	})
 	out.Parameters["foo"] = "baz"
 
@@ -195,7 +196,7 @@ func TestHostVolume_CanonicalizeForUpdate(t *testing.T) {
 		RequestedCapacityMaxBytes: 500000,
 		RequestedCapabilities: []*HostVolumeCapability{{
 			AttachmentMode: HostVolumeAttachmentModeFilesystem,
-			AccessMode:     HostVolumeAccessModeMultiNodeMultiWriter,
+			AccessMode:     HostVolumeAccessModeSingleNodeMultiWriter,
 		}},
 	}
 	existing := &HostVolume{
@@ -240,7 +241,7 @@ func TestHostVolume_CanonicalizeForUpdate(t *testing.T) {
 
 	must.Eq(t, []*HostVolumeCapability{{
 		AttachmentMode: HostVolumeAttachmentModeFilesystem,
-		AccessMode:     HostVolumeAccessModeMultiNodeMultiWriter,
+		AccessMode:     HostVolumeAccessModeSingleNodeMultiWriter,
 	}}, vol.RequestedCapabilities)
 
 	must.Eq(t, "/var/nomad/alloc_mounts/82f357d6.ext4", vol.HostPath)
@@ -251,3 +252,120 @@ func TestHostVolume_CanonicalizeForUpdate(t *testing.T) {
 	must.Nil(t, vol.Allocations)
 
 }
+
+func TestHostVolume_IsAvailable(t *testing.T) {
+
+	allCaps := []*HostVolumeCapability{}
+
+	for _, accessMode := range []HostVolumeAccessMode{
+		HostVolumeAccessModeSingleNodeReader,
+		HostVolumeAccessModeSingleNodeWriter,
+		HostVolumeAccessModeSingleNodeSingleWriter,
+		HostVolumeAccessModeSingleNodeMultiWriter,
+	} {
+		for _, attachMode := range []HostVolumeAttachmentMode{
+			HostVolumeAttachmentModeFilesystem, HostVolumeAttachmentModeBlockDevice,
+		} {
+			allCaps = append(allCaps, &HostVolumeCapability{
+				AttachmentMode: attachMode,
+				AccessMode:     accessMode,
+			})
+		}
+	}
+
+	testCases := []struct {
+		name        string
+		hasAllocs   []string
+		hasWriters  []string
+		hasCaps     []*HostVolumeCapability
+		req         *HostVolumeCapability
+		readOnly    bool
+		prevAllocID string
+		expect      bool
+	}{
+		{
+			name: "enforce attachment mode",
+			hasCaps: []*HostVolumeCapability{{
+				AttachmentMode: HostVolumeAttachmentModeBlockDevice,
+				AccessMode:     HostVolumeAccessModeSingleNodeSingleWriter,
+			}},
+			req: &HostVolumeCapability{
+				AttachmentMode: HostVolumeAttachmentModeFilesystem,
+				AccessMode:     HostVolumeAccessModeSingleNodeSingleWriter,
+			},
+			expect: false,
+		},
+		{
+			name:      "enforce read only",
+			hasAllocs: []string{"a", "b", "c"},
+			req: &HostVolumeCapability{
+				AttachmentMode: HostVolumeAttachmentModeFilesystem,
+				AccessMode:     HostVolumeAccessModeSingleNodeReader,
+			},
+			expect: false,
+		},
+		{
+			name:      "enforce read only ok",
+			hasAllocs: []string{"a", "b", "c"},
+			req: &HostVolumeCapability{
+				AttachmentMode: HostVolumeAttachmentModeFilesystem,
+				AccessMode:     HostVolumeAccessModeSingleNodeReader,
+			},
+			readOnly: true,
+			expect:   true,
+		},
+		{
+			name:       "enforce single writer",
+			hasAllocs:  []string{"a", "b", "c"},
+			hasWriters: []string{"b"},
+			req: &HostVolumeCapability{
+				AttachmentMode: HostVolumeAttachmentModeFilesystem,
+				AccessMode:     HostVolumeAccessModeSingleNodeSingleWriter,
+			},
+			expect: false,
+		},
+		{
+			name:       "enforce single writer ok across deployments",
+			hasAllocs:  []string{"a", "b", "c"},
+			hasWriters: []string{"b"},
+			req: &HostVolumeCapability{
+				AttachmentMode: HostVolumeAttachmentModeFilesystem,
+				AccessMode:     HostVolumeAccessModeSingleNodeSingleWriter,
+			},
+			prevAllocID: "b",
+			expect:      true,
+		},
+		{
+			name:       "multi writer is always ok",
+			hasAllocs:  []string{"a", "b", "c"},
+			hasWriters: []string{"b", "c"},
+			req: &HostVolumeCapability{
+				AttachmentMode: HostVolumeAttachmentModeFilesystem,
+				AccessMode:     HostVolumeAccessModeSingleNodeMultiWriter,
+			},
+			expect: true,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			allocs := helper.ConvertSlice(tc.hasAllocs, func(id string) *AllocListStub {
+				return &AllocListStub{ID: id}
+			})
+			vol := &HostVolume{
+				Allocations: allocs,
+				Writers:     tc.hasWriters,
+				State:       HostVolumeStateReady,
+			}
+			if len(tc.hasCaps) > 0 {
+				vol.RequestedCapabilities = tc.hasCaps
+			} else {
+				vol.RequestedCapabilities = allCaps
+			}
+
+			must.Eq(t, tc.expect, vol.IsAvailable(
+				tc.req.AccessMode, tc.req.AttachmentMode, tc.readOnly, tc.prevAllocID))
+		})
+	}
+
+}

nomad/structs/volumes.go

@@ -170,16 +170,22 @@ func (v *VolumeRequest) Validate(jobType string, taskGroupCount, canaries int) e
 	switch v.Type {
 
 	case VolumeTypeHost:
-		if v.AttachmentMode != CSIVolumeAttachmentModeUnknown {
-			addErr("host volumes cannot have an attachment mode")
-		}
-		if v.AccessMode != CSIVolumeAccessModeUnknown {
-			addErr("host volumes cannot have an access mode")
-		}
 		if v.MountOptions != nil {
+			// TODO(1.10.0): support mount options for dynamic host volumes
 			addErr("host volumes cannot have mount options")
 		}
 
+		switch v.AccessMode {
+		case CSIVolumeAccessModeSingleNodeReader, CSIVolumeAccessModeMultiNodeReader:
+			if !v.ReadOnly {
+				addErr("%s volumes must be read-only", v.AccessMode)
+			}
+		default:
+			// dynamic host volumes are all "per node" so there's no way to
+			// validate that other access modes work for a given volume until we
+			// have access to other allocations (in the scheduler)
+		}
+
 	case VolumeTypeCSI:
 
 		switch v.AttachmentMode {

scheduler/feasible.go

@@ -137,9 +137,10 @@ func NewRandomIterator(ctx Context, nodes []*structs.Node) *StaticIterator {
 // HostVolumeChecker is a FeasibilityChecker which returns whether a node has
 // the host volumes necessary to schedule a task group.
 type HostVolumeChecker struct {
-	ctx        Context
-	volumeReqs []*structs.VolumeRequest
-	namespace  string
+	ctx                  Context
+	volumeReqs           []*structs.VolumeRequest
+	namespace            string
+	previousAllocationID string
 }
 
 // NewHostVolumeChecker creates a HostVolumeChecker from a set of volumes
@@ -151,9 +152,10 @@ func NewHostVolumeChecker(ctx Context) *HostVolumeChecker {
 }
 
 // SetVolumes takes the volumes required by a task group and updates the checker.
-func (h *HostVolumeChecker) SetVolumes(allocName string, ns string, volumes map[string]*structs.VolumeRequest) {
+func (h *HostVolumeChecker) SetVolumes(allocName string, ns string, volumes map[string]*structs.VolumeRequest, prevAllocID string) {
 	h.namespace = ns
 	h.volumeReqs = []*structs.VolumeRequest{}
+	h.previousAllocationID = prevAllocID
 	for _, req := range volumes {
 		if req.Type != structs.VolumeTypeHost {
 			continue // filter CSI volumes
@@ -194,26 +196,20 @@ func (h *HostVolumeChecker) hasVolumes(n *structs.Node) bool {
 		}
 
 		if volCfg.ID != "" { // dynamic host volume
-			vol, err := h.ctx.State().HostVolumeByID(nil, h.namespace, volCfg.ID, false)
+			vol, err := h.ctx.State().HostVolumeByID(nil, h.namespace, volCfg.ID, true)
 			if err != nil || vol == nil {
 				// node fingerprint has a dynamic volume that's no longer in the
 				// state store; this is only possible if the batched fingerprint
 				// update from a delete RPC is written before the delete RPC's
 				// raft entry completes
 				return false
 			}
-			if vol.State != structs.HostVolumeStateReady {
-				return false
-			}
-			var capOk bool
-			for _, cap := range vol.RequestedCapabilities {
-				if req.AccessMode == structs.CSIVolumeAccessMode(cap.AccessMode) &&
-					req.AttachmentMode == structs.CSIVolumeAttachmentMode(cap.AttachmentMode) {
-					capOk = true
-					break
-				}
-			}
-			if !capOk {
+			if !vol.IsAvailable(
+				structs.HostVolumeAccessMode(req.AccessMode),
+				structs.HostVolumeAttachmentMode(req.AttachmentMode),
+				req.ReadOnly,
+				h.previousAllocationID,
+			) {
 				return false
 			}
 		} else if !req.ReadOnly {

scheduler/generic_sched.go

@@ -838,6 +838,7 @@ func getSelectOptions(prevAllocation *structs.Allocation, preferredNode *structs
 			}
 		}
 		selectOptions.PenaltyNodeIDs = penaltyNodes
+		selectOptions.PreviousAllocID = prevAllocation.ID
 	}
 	if preferredNode != nil {
 		selectOptions.PreferredNodes = []*structs.Node{preferredNode}