Add comments and small improvements to cgroup fingerprinter

client/driver/exec.go

@@ -46,7 +46,7 @@ func NewExecDriver(ctx *DriverContext) Driver {
 
 func (d *ExecDriver) Fingerprint(cfg *config.Config, node *structs.Node) (bool, error) {
 	// Only enable if cgroups are available and we are root
-	if _, ok := node.Attributes["cgroup.mountpoint"]; !ok {
+	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 {

client/driver/exec_test.go

@@ -23,7 +23,7 @@ func TestExecDriver_Fingerprint(t *testing.T) {
 	d := NewExecDriver(driverCtx)
 	node := &structs.Node{
 		Attributes: map[string]string{
-			"cgroup.mountpoint": "/sys/fs/cgroup",
+			"unique.cgroup.mountpoint": "/sys/fs/cgroup",
 		},
 	}
 	apply, err := d.Fingerprint(&config.Config{}, node)

client/fingerprint/cgroup.go

@@ -12,6 +12,7 @@ import (
 const (
 	cgroupAvailable   = "available"
 	cgroupUnavailable = "unavailable"
+	interval          = 15
 )
 
 type CGroupFingerprint struct {
@@ -36,6 +37,7 @@ func (b *DefaultMountPointDetector) MountPoint() (string, error) {
 	return FindCgroupMountpointDir()
 }
 
+// NewCGroupFingerprint returns a new cgroup fingerprinter
 func NewCGroupFingerprint(logger *log.Logger) Fingerprint {
 	f := &CGroupFingerprint{
 		logger:             logger,
@@ -45,10 +47,11 @@ func NewCGroupFingerprint(logger *log.Logger) Fingerprint {
 	return f
 }
 
+// Fingerprint tries to find a valid cgroup moint point
 func (f *CGroupFingerprint) Fingerprint(cfg *client.Config, node *structs.Node) (bool, error) {
-	// Try to find a valid cgroup mount point
 	mount, err := f.mountPointDetector.MountPoint()
 	if err != nil {
+		f.clearCGroupAttributes(node)
 		return false, fmt.Errorf("Failed to discover cgroup mount point: %s", err)
 	}
 
@@ -64,7 +67,7 @@ func (f *CGroupFingerprint) Fingerprint(cfg *client.Config, node *structs.Node)
 		return true, nil
 	}
 
-	node.Attributes["cgroup.mountpoint"] = mount
+	node.Attributes["unique.cgroup.mountpoint"] = mount
 
 	if f.lastState == cgroupUnavailable {
 		f.logger.Printf("[INFO] fingerprint.cgroups: cgroups are available")
@@ -73,10 +76,13 @@ func (f *CGroupFingerprint) Fingerprint(cfg *client.Config, node *structs.Node)
 	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, "cgroup.mountpoint")
+	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, 15 * time.Second
+	return true, interval * time.Second
 }

client/fingerprint/cgroup_linux.go

@@ -6,6 +6,8 @@ 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 {

client/fingerprint/cgroup_test.go

@@ -54,7 +54,7 @@ func TestCGroupFingerprint(t *testing.T) {
 	if ok {
 		t.Fatalf("should not apply")
 	}
-	if a, ok := node.Attributes["cgroup.mountpoint"]; ok {
+	if a, ok := node.Attributes["unique.cgroup.mountpoint"]; ok {
 		t.Fatalf("unexpected attribute found, %s", a)
 	}
 
@@ -75,7 +75,7 @@ func TestCGroupFingerprint(t *testing.T) {
 	if !ok {
 		t.Fatalf("should apply")
 	}
-	assertNodeAttributeContains(t, node, "cgroup.mountpoint")
+	assertNodeAttributeContains(t, node, "unique.cgroup.mountpoint")
 
 	f = &CGroupFingerprint{
 		logger:             testLogger(),
@@ -94,7 +94,7 @@ func TestCGroupFingerprint(t *testing.T) {
 	if !ok {
 		t.Fatalf("should apply")
 	}
-	if a, ok := node.Attributes["cgroup.mountpoint"]; ok {
+	if a, ok := node.Attributes["unique.cgroup.mountpoint"]; ok {
 		t.Fatalf("unexpected attribute found, %s", a)
 	}
 }

client/fingerprint/cgroup_universal.go

@@ -2,7 +2,7 @@
 
 package fingerprint
 
-// cgroups only exist on Linux
+// FindCgroupMountpointDir returns an empty path on non-Linux systems
 func FindCgroupMountpointDir() (string, error) {
 	return "", nil
 }

client/fingerprint/fingerprint.go

@@ -12,7 +12,7 @@ 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",
@@ -43,7 +43,6 @@ var builtinFingerprintMap = map[string]Factory{
 }
 
 // NewFingerprint is used to instantiate and return a new fingerprint
-
 // given the name and a logger
 func NewFingerprint(name string, logger *log.Logger) (Fingerprint, error) {
 	// Lookup the factory function