client: Add volume_hook for mounting volumes

client/allocrunner/taskrunner/task_runner_hooks.go

@@ -61,6 +61,7 @@ func (tr *TaskRunner) initHooks() {
 		newTaskDirHook(tr, hookLogger),
 		newLogMonHook(tr.logmonHookConfig, hookLogger),
 		newDispatchHook(tr.Alloc(), hookLogger),
+		newVolumeHook(tr, hookLogger),
 		newArtifactHook(tr, hookLogger),
 		newStatsHook(tr, tr.clientConfig.StatsCollectionInterval, hookLogger),
 		newDeviceHook(tr.devicemanager, hookLogger),

client/allocrunner/taskrunner/volume_hook.go

@@ -0,0 +1,123 @@
+package taskrunner
+
+import (
+	"context"
+	"fmt"
+
+	log "github.com/hashicorp/go-hclog"
+	multierror "github.com/hashicorp/go-multierror"
+	"github.com/hashicorp/nomad/client/allocrunner/interfaces"
+	"github.com/hashicorp/nomad/nomad/structs"
+	"github.com/hashicorp/nomad/plugins/drivers"
+)
+
+type volumeHook struct {
+	alloc  *structs.Allocation
+	runner *TaskRunner
+	logger log.Logger
+}
+
+func newVolumeHook(runner *TaskRunner, logger log.Logger) *volumeHook {
+	h := &volumeHook{
+		alloc:  runner.Alloc(),
+		runner: runner,
+	}
+	h.logger = logger.Named(h.Name())
+	return h
+}
+
+func (*volumeHook) Name() string {
+	return "volumes"
+}
+
+func validateHostVolumes(requested map[string]*structs.VolumeRequest, client map[string]*structs.ClientHostVolumeConfig) error {
+	var result error
+
+	for n, req := range requested {
+		if req.Volume.Type != "host" {
+			continue
+		}
+
+		cfg, err := structs.ParseHostVolumeConfig(req.Config)
+		if err != nil {
+			result = multierror.Append(result, fmt.Errorf("failed to parse config for %s: %v", n, err))
+		}
+
+		_, ok := client[cfg.Source]
+		if !ok {
+			result = multierror.Append(result, fmt.Errorf("missing %s", cfg.Source))
+		}
+	}
+
+	return result
+}
+
+func (h *volumeHook) hostVolumeMountConfigurations(vmounts []*structs.VolumeMount, volumes map[string]*structs.VolumeRequest, client map[string]*structs.ClientHostVolumeConfig) ([]*drivers.MountConfig, error) {
+	var mounts []*drivers.MountConfig
+	for _, m := range vmounts {
+		req, ok := volumes[m.Volume]
+		if !ok {
+			// Should never happen unless we misvalidated on job submission
+			return nil, fmt.Errorf("No group volume declaration found named: %s", m.Volume)
+		}
+
+		cfg, err := structs.ParseHostVolumeConfig(req.Config)
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse config for %s: %v", m.Volume, err)
+		}
+
+		hostVolume, ok := client[cfg.Source]
+		if !ok {
+			// Should never happen, but unless the client volumes were mutated during
+			// the execution of this hook.
+			return nil, fmt.Errorf("No host volume named: %s", cfg.Source)
+		}
+
+		mcfg := &drivers.MountConfig{
+			HostPath: hostVolume.Source,
+			TaskPath: m.Destination,
+			Readonly: hostVolume.ReadOnly || req.Volume.ReadOnly || m.ReadOnly,
+		}
+		mounts = append(mounts, mcfg)
+	}
+
+	return mounts, nil
+}
+
+func (h *volumeHook) Prestart(ctx context.Context, req *interfaces.TaskPrestartRequest, resp *interfaces.TaskPrestartResponse) error {
+	volumes := h.alloc.Job.LookupTaskGroup(h.alloc.TaskGroup).Volumes
+	mounts := h.runner.hookResources.getMounts()
+
+	hostVolumes := h.runner.clientConfig.Node.HostVolumes
+
+	// Always validate volumes to ensure that we do not allow volumes to be used
+	// if a host is restarted and loses the host volume configuration.
+	if err := validateHostVolumes(volumes, hostVolumes); err != nil {
+		h.logger.Error("Requested Host Volume does not exist", "existing", hostVolumes, "requested", volumes)
+		return fmt.Errorf("host volume validation error: %v", err)
+	}
+
+	requestedMounts, err := h.hostVolumeMountConfigurations(req.Task.VolumeMounts, volumes, hostVolumes)
+	if err != nil {
+		h.logger.Error("Failed to generate volume mounts", "error", err)
+		return err
+	}
+
+	// Because this hook is also ran on restores, we only add mounts that do not
+	// already exist. Although this loop is somewhat expensive, there are only
+	// a small number of mounts that exist within most individual tasks. We may
+	// want to revisit this using a `hookdata` param to be "mount only once"
+REQUESTED:
+	for _, m := range requestedMounts {
+		for _, em := range mounts {
+			if em.IsEqual(m) {
+				continue REQUESTED
+			}
+		}
+
+		mounts = append(mounts, m)
+	}
+
+	h.runner.hookResources.setMounts(mounts)
+	return nil
+}

plugins/drivers/driver.go

@@ -314,6 +314,12 @@ type MountConfig struct {
 	Readonly bool
 }
 
+func (m *MountConfig) IsEqual(o *MountConfig) bool {
+	return m.TaskPath == o.TaskPath &&
+		m.HostPath == o.HostPath &&
+		m.Readonly == o.Readonly
+}
+
 func (m *MountConfig) Copy() *MountConfig {
 	if m == nil {
 		return nil