CSI: improve controller RPC reliability

.changelog/17996.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+csi: Fixed a bug in sending concurrent requests to CSI controller plugins by serializing them per plugin
+```

nomad/client_csi_endpoint.go

@@ -5,7 +5,7 @@ package nomad
 
 import (
 	"fmt"
-	"math/rand"
+	"sort"
 	"strings"
 	"time"
 
@@ -262,9 +262,9 @@ func (a *ClientCSI) clientIDsForController(pluginID string) ([]string, error) {
 
 	ws := memdb.NewWatchSet()
 
-	// note: plugin IDs are not scoped to region/DC but volumes are.
-	// so any node we get for a controller is already in the same
-	// region/DC for the volume.
+	// note: plugin IDs are not scoped to region but volumes are. so any Nomad
+	// client we get for a controller is already in the same region for the
+	// volume.
 	plugin, err := snap.CSIPluginByID(ws, pluginID)
 	if err != nil {
 		return nil, fmt.Errorf("error getting plugin: %s, %v", pluginID, err)
@@ -273,13 +273,10 @@ func (a *ClientCSI) clientIDsForController(pluginID string) ([]string, error) {
 		return nil, fmt.Errorf("plugin missing: %s", pluginID)
 	}
 
-	// iterating maps is "random" but unspecified and isn't particularly
-	// random with small maps, so not well-suited for load balancing.
-	// so we shuffle the keys and iterate over them.
 	clientIDs := []string{}
 
 	for clientID, controller := range plugin.Controllers {
-		if !controller.IsController() {
+		if !controller.IsController() || !controller.Healthy {
 			// we don't have separate types for CSIInfo depending on
 			// whether it's a controller or node. this error shouldn't
 			// make it to production but is to aid developers during
@@ -295,9 +292,11 @@ func (a *ClientCSI) clientIDsForController(pluginID string) ([]string, error) {
 		return nil, fmt.Errorf("failed to find clients running controller plugin %q", pluginID)
 	}
 
-	rand.Shuffle(len(clientIDs), func(i, j int) {
-		clientIDs[i], clientIDs[j] = clientIDs[j], clientIDs[i]
-	})
+	// Many plugins don't handle concurrent requests as described in the spec,
+	// and have undocumented expectations of using k8s-specific sidecars to
+	// leader elect. Sort the client IDs so that we prefer sending requests to
+	// the same controller to hack around this.
+	clientIDs = sort.StringSlice(clientIDs)
 
 	return clientIDs, nil
 }

nomad/csi_endpoint.go

@@ -4,6 +4,7 @@
 package nomad
 
 import (
+	"context"
 	"fmt"
 	"net/http"
 	"strings"
@@ -549,7 +550,9 @@ func (v *CSIVolume) controllerPublishVolume(req *structs.CSIVolumeClaimRequest,
 	cReq.PluginID = plug.ID
 	cResp := &cstructs.ClientCSIControllerAttachVolumeResponse{}
 
-	err = v.srv.RPC(method, cReq, cResp)
+	err = v.serializedControllerRPC(plug.ID, func() error {
+		return v.srv.RPC(method, cReq, cResp)
+	})
 	if err != nil {
 		if strings.Contains(err.Error(), "FailedPrecondition") {
 			return fmt.Errorf("%v: %v", structs.ErrCSIClientRPCRetryable, err)
@@ -586,6 +589,57 @@ func (v *CSIVolume) volAndPluginLookup(namespace, volID string) (*structs.CSIPlu
 	return plug, vol, nil
 }
 
+// serializedControllerRPC ensures we're only sending a single controller RPC to
+// a given plugin if the RPC can cause conflicting state changes.
+//
+// The CSI specification says that we SHOULD send no more than one in-flight
+// request per *volume* at a time, with an allowance for losing state
+// (ex. leadership transitions) which the plugins SHOULD handle gracefully.
+//
+// In practice many CSI plugins rely on k8s-specific sidecars for serializing
+// storage provider API calls globally (ex. concurrently attaching EBS volumes
+// to an EC2 instance results in a race for device names). So we have to be much
+// more conservative about concurrency in Nomad than the spec allows.
+func (v *CSIVolume) serializedControllerRPC(pluginID string, fn func() error) error {
+
+	for {
+		v.srv.volumeControllerLock.Lock()
+		future := v.srv.volumeControllerFutures[pluginID]
+		if future == nil {
+			future, futureDone := context.WithCancel(v.srv.shutdownCtx)
+			v.srv.volumeControllerFutures[pluginID] = future
+			v.srv.volumeControllerLock.Unlock()
+
+			err := fn()
+
+			// close the future while holding the lock and not in a defer so
+			// that we can ensure we've cleared it from the map before allowing
+			// anyone else to take the lock and write a new one
+			v.srv.volumeControllerLock.Lock()
+			futureDone()
+			delete(v.srv.volumeControllerFutures, pluginID)
+			v.srv.volumeControllerLock.Unlock()
+
+			return err
+		} else {
+			v.srv.volumeControllerLock.Unlock()
+
+			select {
+			case <-future.Done():
+				continue
+			case <-v.srv.shutdownCh:
+				// The csi_hook publish workflow on the client will retry if it
+				// gets this error. On unpublish, we don't want to block client
+				// shutdown so we give up on error. The new leader's
+				// volumewatcher will iterate all the claims at startup to
+				// detect this and mop up any claims in the NodeDetached state
+				// (volume GC will run periodically as well)
+				return structs.ErrNoLeader
+			}
+		}
+	}
+}
+
 // allowCSIMount is called on Job register to check mount permission
 func allowCSIMount(aclObj *acl.ACL, namespace string) bool {
 	return aclObj.AllowPluginRead() &&
@@ -863,8 +917,11 @@ func (v *CSIVolume) controllerUnpublishVolume(vol *structs.CSIVolume, claim *str
 		Secrets:         vol.Secrets,
 	}
 	req.PluginID = vol.PluginID
-	err = v.srv.RPC("ClientCSI.ControllerDetachVolume", req,
-		&cstructs.ClientCSIControllerDetachVolumeResponse{})
+
+	err = v.serializedControllerRPC(vol.PluginID, func() error {
+		return v.srv.RPC("ClientCSI.ControllerDetachVolume", req,
+			&cstructs.ClientCSIControllerDetachVolumeResponse{})
+	})
 	if err != nil {
 		return fmt.Errorf("could not detach from controller: %v", err)
 	}
@@ -1139,7 +1196,9 @@ func (v *CSIVolume) deleteVolume(vol *structs.CSIVolume, plugin *structs.CSIPlug
 	cReq.PluginID = plugin.ID
 	cResp := &cstructs.ClientCSIControllerDeleteVolumeResponse{}
 
-	return v.srv.RPC(method, cReq, cResp)
+	return v.serializedControllerRPC(plugin.ID, func() error {
+		return v.srv.RPC(method, cReq, cResp)
+	})
 }
 
 func (v *CSIVolume) ListExternal(args *structs.CSIVolumeExternalListRequest, reply *structs.CSIVolumeExternalListResponse) error {
@@ -1286,7 +1345,9 @@ func (v *CSIVolume) CreateSnapshot(args *structs.CSISnapshotCreateRequest, reply
 		}
 		cReq.PluginID = pluginID
 		cResp := &cstructs.ClientCSIControllerCreateSnapshotResponse{}
-		err = v.srv.RPC(method, cReq, cResp)
+		err = v.serializedControllerRPC(pluginID, func() error {
+			return v.srv.RPC(method, cReq, cResp)
+		})
 		if err != nil {
 			multierror.Append(&mErr, fmt.Errorf("could not create snapshot: %v", err))
 			continue
@@ -1360,7 +1421,9 @@ func (v *CSIVolume) DeleteSnapshot(args *structs.CSISnapshotDeleteRequest, reply
 		cReq := &cstructs.ClientCSIControllerDeleteSnapshotRequest{ID: snap.ID}
 		cReq.PluginID = plugin.ID
 		cResp := &cstructs.ClientCSIControllerDeleteSnapshotResponse{}
-		err = v.srv.RPC(method, cReq, cResp)
+		err = v.serializedControllerRPC(plugin.ID, func() error {
+			return v.srv.RPC(method, cReq, cResp)
+		})
 		if err != nil {
 			multierror.Append(&mErr, fmt.Errorf("could not delete %q: %v", snap.ID, err))
 		}

nomad/csi_endpoint_test.go

@@ -6,6 +6,7 @@ package nomad
 import (
 	"fmt"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -21,6 +22,7 @@ import (
 	cconfig "github.com/hashicorp/nomad/client/config"
 	cstructs "github.com/hashicorp/nomad/client/structs"
 	"github.com/hashicorp/nomad/helper/uuid"
+	"github.com/hashicorp/nomad/lib/lang"
 	"github.com/hashicorp/nomad/nomad/mock"
 	"github.com/hashicorp/nomad/nomad/state"
 	"github.com/hashicorp/nomad/nomad/structs"
@@ -1971,3 +1973,49 @@ func TestCSI_RPCVolumeAndPluginLookup(t *testing.T) {
 	require.Nil(t, vol)
 	require.EqualError(t, err, fmt.Sprintf("volume not found: %s", id2))
 }
+
+func TestCSI_SerializedControllerRPC(t *testing.T) {
+	ci.Parallel(t)
+
+	srv, shutdown := TestServer(t, func(c *Config) { c.NumSchedulers = 0 })
+	defer shutdown()
+	testutil.WaitForLeader(t, srv.RPC)
+
+	var wg sync.WaitGroup
+	wg.Add(3)
+
+	timeCh := make(chan lang.Pair[string, time.Duration])
+
+	testFn := func(pluginID string, dur time.Duration) {
+		defer wg.Done()
+		c := NewCSIVolumeEndpoint(srv, nil)
+		now := time.Now()
+		err := c.serializedControllerRPC(pluginID, func() error {
+			time.Sleep(dur)
+			return nil
+		})
+		elapsed := time.Since(now)
+		timeCh <- lang.Pair[string, time.Duration]{pluginID, elapsed}
+		must.NoError(t, err)
+	}
+
+	go testFn("plugin1", 50*time.Millisecond)
+	go testFn("plugin2", 50*time.Millisecond)
+	go testFn("plugin1", 50*time.Millisecond)
+
+	totals := map[string]time.Duration{}
+	for i := 0; i < 3; i++ {
+		pair := <-timeCh
+		totals[pair.First] += pair.Second
+	}
+
+	wg.Wait()
+
+	// plugin1 RPCs should block each other
+	must.GreaterEq(t, 150*time.Millisecond, totals["plugin1"])
+	must.Less(t, 200*time.Millisecond, totals["plugin1"])
+
+	// plugin1 RPCs should not block plugin2 RPCs
+	must.GreaterEq(t, 50*time.Millisecond, totals["plugin2"])
+	must.Less(t, 100*time.Millisecond, totals["plugin2"])
+}

nomad/server.go

@@ -218,6 +218,13 @@ type Server struct {
 	// volumeWatcher is used to release volume claims
 	volumeWatcher *volumewatcher.Watcher
 
+	// volumeControllerFutures is a map of plugin IDs to pending controller RPCs. If
+	// no RPC is pending for a given plugin, this may be nil.
+	volumeControllerFutures map[string]context.Context
+
+	// volumeControllerLock synchronizes access controllerFutures map
+	volumeControllerLock sync.Mutex
+
 	// keyringReplicator is used to replicate root encryption keys from the
 	// leader
 	keyringReplicator *KeyringReplicator
@@ -445,6 +452,7 @@ func NewServer(config *Config, consulCatalog consul.CatalogAPI, consulConfigEntr
 		s.logger.Error("failed to create volume watcher", "error", err)
 		return nil, fmt.Errorf("failed to create volume watcher: %v", err)
 	}
+	s.volumeControllerFutures = map[string]context.Context{}
 
 	// Start the eval broker notification system so any subscribers can get
 	// updates when the processes SetEnabled is triggered.