Add periodic cgroup fingerprinter

client/driver/exec.go

@@ -5,15 +5,13 @@ import (
 	"fmt"
 	"log"
 	"path/filepath"
-	"runtime"
 	"syscall"
 	"time"
 
 	"github.com/hashicorp/nomad/client/allocdir"
 	"github.com/hashicorp/nomad/client/config"
 	"github.com/hashicorp/nomad/client/driver/executor"
 	cstructs "github.com/hashicorp/nomad/client/driver/structs"
-	"github.com/hashicorp/nomad/client/fingerprint"
 	"github.com/hashicorp/nomad/client/getter"
 	"github.com/hashicorp/nomad/nomad/structs"
 	"github.com/mitchellh/mapstructure"
@@ -23,8 +21,8 @@ import (
 // features.
 type ExecDriver struct {
 	DriverContext
-	fingerprint.StaticFingerprinter
 }
+
 type ExecDriverConfig struct {
 	ArtifactSource string   `mapstructure:"artifact_source"`
 	Checksum       string   `mapstructure:"checksum"`
@@ -47,9 +45,9 @@ func NewExecDriver(ctx *DriverContext) Driver {
 }
 
 func (d *ExecDriver) Fingerprint(cfg *config.Config, node *structs.Node) (bool, error) {
-	// Only enable if we are root on linux.
-	if runtime.GOOS != "linux" {
-		d.logger.Printf("[DEBUG] driver.exec: only available on linux, disabling")
+	// Only enable if cgroups are available and we are root
+	if _, ok := node.Attributes["unique.cgroup.mountpoint"]; !ok {
+		d.logger.Printf("[DEBUG] driver.exec: cgroups unavailable, disabling")
 		return false, nil
 	} else if syscall.Geteuid() != 0 {
 		d.logger.Printf("[DEBUG] driver.exec: must run as root user, disabling")
@@ -60,6 +58,10 @@ func (d *ExecDriver) Fingerprint(cfg *config.Config, node *structs.Node) (bool,
 	return true, nil
 }
 
+func (d *ExecDriver) Periodic() (bool, time.Duration) {
+	return true, 15 * time.Second
+}
+
 func (d *ExecDriver) Start(ctx *ExecContext, task *structs.Task) (DriverHandle, error) {
 	var driverConfig ExecDriverConfig
 	if err := mapstructure.WeakDecode(task.Config, &driverConfig); err != nil {

client/driver/exec_test.go

@@ -22,7 +22,9 @@ func TestExecDriver_Fingerprint(t *testing.T) {
 	driverCtx, _ := testDriverContexts(&structs.Task{Name: "foo"})
 	d := NewExecDriver(driverCtx)
 	node := &structs.Node{
-		Attributes: make(map[string]string),
+		Attributes: map[string]string{
+			"unique.cgroup.mountpoint": "/sys/fs/cgroup",
+		},
 	}
 	apply, err := d.Fingerprint(&config.Config{}, node)
 	if err != nil {

client/fingerprint/cgroup.go

@@ -0,0 +1,88 @@
+package fingerprint
+
+import (
+	"fmt"
+	"log"
+	"time"
+
+	client "github.com/hashicorp/nomad/client/config"
+	"github.com/hashicorp/nomad/nomad/structs"
+)
+
+const (
+	cgroupAvailable   = "available"
+	cgroupUnavailable = "unavailable"
+	interval          = 15
+)
+
+type CGroupFingerprint struct {
+	logger             *log.Logger
+	lastState          string
+	mountPointDetector MountPointDetector
+}
+
+// An interface to isolate calls to the cgroup library
+// This facilitates testing where we can implement
+// fake mount points to test various code paths
+type MountPointDetector interface {
+	MountPoint() (string, error)
+}
+
+// Implements the interface detector which calls the cgroups library directly
+type DefaultMountPointDetector struct {
+}
+
+// Call out to the default cgroup library
+func (b *DefaultMountPointDetector) MountPoint() (string, error) {
+	return FindCgroupMountpointDir()
+}
+
+// NewCGroupFingerprint returns a new cgroup fingerprinter
+func NewCGroupFingerprint(logger *log.Logger) Fingerprint {
+	f := &CGroupFingerprint{
+		logger:             logger,
+		lastState:          cgroupUnavailable,
+		mountPointDetector: &DefaultMountPointDetector{},
+	}
+	return f
+}
+
+// Fingerprint tries to find a valid cgroup moint point
+func (f *CGroupFingerprint) Fingerprint(cfg *client.Config, node *structs.Node) (bool, error) {
+	mount, err := f.mountPointDetector.MountPoint()
+	if err != nil {
+		f.clearCGroupAttributes(node)
+		return false, fmt.Errorf("Failed to discover cgroup mount point: %s", err)
+	}
+
+	// Check if a cgroup mount point was found
+	if mount == "" {
+		// Clear any attributes from the previous fingerprint.
+		f.clearCGroupAttributes(node)
+
+		if f.lastState == cgroupAvailable {
+			f.logger.Printf("[INFO] fingerprint.cgroups: cgroups are unavailable")
+		}
+		f.lastState = cgroupUnavailable
+		return true, nil
+	}
+
+	node.Attributes["unique.cgroup.mountpoint"] = mount
+
+	if f.lastState == cgroupUnavailable {
+		f.logger.Printf("[INFO] fingerprint.cgroups: cgroups are available")
+	}
+	f.lastState = cgroupAvailable
+	return true, nil
+}
+
+// clearCGroupAttributes clears any node attributes related to cgroups that might
+// have been set in a previous fingerprint run.
+func (f *CGroupFingerprint) clearCGroupAttributes(n *structs.Node) {
+	delete(n.Attributes, "unique.cgroup.mountpoint")
+}
+
+// Periodic determines the interval at which the periodic fingerprinter will run.
+func (f *CGroupFingerprint) Periodic() (bool, time.Duration) {
+	return true, interval * time.Second
+}

client/fingerprint/cgroup_linux.go

@@ -0,0 +1,24 @@
+// +build linux
+
+package fingerprint
+
+import (
+	"github.com/opencontainers/runc/libcontainer/cgroups"
+)
+
+// FindCgroupMountpointDir is used to find the cgroup mount point on a Linux
+// system.
+func FindCgroupMountpointDir() (string, error) {
+	mount, err := cgroups.FindCgroupMountpointDir()
+	if err != nil {
+		switch e := err.(type) {
+		case *cgroups.NotFoundError:
+			// It's okay if the mount point is not discovered
+			return "", nil
+		default:
+			// All other errors are passed back as is
+			return "", e
+		}
+	}
+	return mount, nil
+}

client/fingerprint/cgroup_test.go

@@ -0,0 +1,100 @@
+package fingerprint
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/hashicorp/nomad/client/config"
+	"github.com/hashicorp/nomad/nomad/structs"
+)
+
+// A fake mount point detector that returns an empty path
+type MountPointDetectorNoMountPoint struct{}
+
+func (m *MountPointDetectorNoMountPoint) MountPoint() (string, error) {
+	return "", nil
+}
+
+// A fake mount point detector that returns an error
+type MountPointDetectorMountPointFail struct{}
+
+func (m *MountPointDetectorMountPointFail) MountPoint() (string, error) {
+	return "", fmt.Errorf("cgroup mountpoint discovery failed")
+}
+
+// A fake mount point detector that returns a valid path
+type MountPointDetectorValidMountPoint struct{}
+
+func (m *MountPointDetectorValidMountPoint) MountPoint() (string, error) {
+	return "/sys/fs/cgroup", nil
+}
+
+// A fake mount point detector that returns an empty path
+type MountPointDetectorEmptyMountPoint struct{}
+
+func (m *MountPointDetectorEmptyMountPoint) MountPoint() (string, error) {
+	return "", nil
+}
+
+func TestCGroupFingerprint(t *testing.T) {
+	f := &CGroupFingerprint{
+		logger:             testLogger(),
+		lastState:          cgroupUnavailable,
+		mountPointDetector: &MountPointDetectorMountPointFail{},
+	}
+
+	node := &structs.Node{
+		Attributes: make(map[string]string),
+	}
+
+	ok, err := f.Fingerprint(&config.Config{}, node)
+	if err == nil {
+		t.Fatalf("expected an error")
+	}
+	if ok {
+		t.Fatalf("should not apply")
+	}
+	if a, ok := node.Attributes["unique.cgroup.mountpoint"]; ok {
+		t.Fatalf("unexpected attribute found, %s", a)
+	}
+
+	f = &CGroupFingerprint{
+		logger:             testLogger(),
+		lastState:          cgroupUnavailable,
+		mountPointDetector: &MountPointDetectorValidMountPoint{},
+	}
+
+	node = &structs.Node{
+		Attributes: make(map[string]string),
+	}
+
+	ok, err = f.Fingerprint(&config.Config{}, node)
+	if err != nil {
+		t.Fatalf("unexpected error, %s", err)
+	}
+	if !ok {
+		t.Fatalf("should apply")
+	}
+	assertNodeAttributeContains(t, node, "unique.cgroup.mountpoint")
+
+	f = &CGroupFingerprint{
+		logger:             testLogger(),
+		lastState:          cgroupUnavailable,
+		mountPointDetector: &MountPointDetectorEmptyMountPoint{},
+	}
+
+	node = &structs.Node{
+		Attributes: make(map[string]string),
+	}
+
+	ok, err = f.Fingerprint(&config.Config{}, node)
+	if err != nil {
+		t.Fatalf("unexpected error, %s", err)
+	}
+	if !ok {
+		t.Fatalf("should apply")
+	}
+	if a, ok := node.Attributes["unique.cgroup.mountpoint"]; ok {
+		t.Fatalf("unexpected attribute found, %s", a)
+	}
+}

client/fingerprint/cgroup_universal.go

@@ -0,0 +1,8 @@
+// +build !linux
+
+package fingerprint
+
+// FindCgroupMountpointDir returns an empty path on non-Linux systems
+func FindCgroupMountpointDir() (string, error) {
+	return "", nil
+}

client/fingerprint/fingerprint.go

@@ -12,10 +12,11 @@ import (
 // EmptyDuration is to be used by fingerprinters that are not periodic.
 const EmptyDuration = time.Duration(0)
 
-// BuiltinFingerprints is a slice containing the key names of all regestered
+// BuiltinFingerprints is a slice containing the key names of all registered
 // fingerprints available, to provided an ordered iteration
 var BuiltinFingerprints = []string{
 	"arch",
+	"cgroup",
 	"consul",
 	"cpu",
 	"env_aws",
@@ -30,6 +31,7 @@ var BuiltinFingerprints = []string{
 // which are available, corresponding to a key found in BuiltinFingerprints
 var builtinFingerprintMap = map[string]Factory{
 	"arch":    NewArchFingerprint,
+	"cgroup":  NewCGroupFingerprint,
 	"consul":  NewConsulFingerprint,
 	"cpu":     NewCPUFingerprint,
 	"env_aws": NewEnvAWSFingerprint,