Add template option for Cgroups (ncabatoff#199)

Add template tag for Cgroups.  If the cgroup is not available, we simply return an empty array as this
can commonly happen on older kernels using the v1 cgroups (found at `/proc/self/cgroups` instead of `/proc/self/cgroup`).

Co-authored-by: Nathan Monfils <[email protected]>
Co-authored-by: Nathan Monfils <[email protected]>

Author: Nathan Monfils

README.md

@@ -107,6 +107,9 @@ Template variables available:
   will only contain a single process.
 - `{{.StartTime}}` contains the start time of the process.  This can be useful
   in conjunction with PID because PIDs get reused over time.
+- `{{.Cgroups}}` contains (if supported) the cgroups of the process
+  (`/proc/self/cgroup`). This is particularly useful for identifying to which container
+  a process belongs.
 
 Using `PID` or `StartTime` is discouraged: this is almost never what you want,
 and is likely to result in high cardinality metrics which Prometheus will have

common.go

@@ -9,6 +9,7 @@ type (
 	ProcAttributes struct {
 		Name      string
 		Cmdline   []string
+		Cgroups   []string
 		Username  string
 		PID       int
 		StartTime time.Time

config/config.go

@@ -50,6 +50,7 @@ type (
 	}
 
 	templateParams struct {
+		Cgroups   []string
 		Comm      string
 		ExeBase   string
 		ExeFull   string
@@ -116,6 +117,7 @@ func (m *matchNamer) MatchAndName(nacl common.ProcAttributes) (bool, string) {
 	var buf bytes.Buffer
 	m.template.Execute(&buf, &templateParams{
 		Comm:      nacl.Name,
+		Cgroups:   nacl.Cgroups,
 		ExeBase:   exebase,
 		ExeFull:   exefull,
 		Matches:   matches,

fixtures/14804/cgroup

@@ -0,0 +1 @@
+0::/system.slice/docker-8dde0b0d6e919baef8d635cd9399b22639ed1e400eaec1b1cb94ff3b216cf3c3.scope

go.mod

@@ -12,7 +12,7 @@ require (
 	github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e // indirect
 	github.com/prometheus/client_golang v1.11.0
 	github.com/prometheus/common v0.26.0
-	github.com/prometheus/procfs v0.6.0
+	github.com/prometheus/procfs v0.7.1
 	github.com/rogpeppe/go-internal v1.8.0 // indirect
 	gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c
 	gopkg.in/yaml.v2 v2.4.0

go.sum

@@ -259,6 +259,8 @@ github.com/prometheus/procfs v0.2.0 h1:wH4vA7pcjKuZzjF7lM8awk4fnuJO6idemZXoKnULU
 github.com/prometheus/procfs v0.2.0/go.mod h1:lV6e/gmhEcM9IjHGsFOCxxuZ+z1YqCvr4OA4YeYWdaU=
 github.com/prometheus/procfs v0.6.0 h1:mxy4L2jP6qMonqmq+aTtOx1ifVWUgG/TAmntgbh3xv4=
 github.com/prometheus/procfs v0.6.0/go.mod h1:cz+aTbrPOrUb4q7XlbU9ygM+/jj0fzG6c1xBZuNvfVA=
+github.com/prometheus/procfs v0.7.1 h1:TlEtJq5GvGqMykEwWzbZWjjztF86swFhsPix1i0bkgA=
+github.com/prometheus/procfs v0.7.1/go.mod h1:cz+aTbrPOrUb4q7XlbU9ygM+/jj0fzG6c1xBZuNvfVA=
 github.com/rcrowley/go-metrics v0.0.0-20181016184325-3113b8401b8a/go.mod h1:bCqnVzQkZxMG4s8nGwiZ5l3QUCyqpo9Y+/ZMZ9VjZe4=
 github.com/rogpeppe/fastuuid v0.0.0-20150106093220-6724a57986af/go.mod h1:XWv6SoW27p1b0cqNHllgS5HIMJraePCO15w5zCzIWYg=
 github.com/rogpeppe/go-internal v1.3.0/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=

proc/base_test.go

@@ -67,7 +67,7 @@ func (n namer) MatchAndName(nacl common.ProcAttributes) (bool, string) {
 
 func newProcIDStatic(pid, ppid int, startTime uint64, name string, cmdline []string) (ID, Static) {
 	return ID{pid, startTime},
-		Static{name, cmdline, ppid, time.Unix(int64(startTime), 0).UTC(), 1000}
+		Static{name, cmdline, []string{}, ppid, time.Unix(int64(startTime), 0).UTC(), 1000}
 }
 
 func newProc(pid int, name string, m Metrics) IDInfo {

proc/read.go

@@ -30,6 +30,7 @@ type (
 	Static struct {
 		Name         string
 		Cmdline      []string
+		Cgroups      []string
 		ParentPid    int
 		StartTime    time.Time
 		EffectiveUID int
@@ -135,6 +136,7 @@ type (
 		stat    *procfs.ProcStat
 		status  *procfs.ProcStatus
 		cmdline []string
+		cgroups []procfs.Cgroup
 		io      *procfs.ProcIO
 		fs      *FS
 		wchan   *string
@@ -299,6 +301,18 @@ func (p *proccache) getStatus() (procfs.ProcStatus, error) {
 	return *p.status, nil
 }
 
+func (p *proccache) getCgroups() ([]procfs.Cgroup, error) {
+	if p.cgroups == nil {
+		cgroups, err := p.Proc.Cgroups()
+		if err != nil {
+			return nil, err
+		}
+		p.cgroups = cgroups
+	}
+
+	return p.cgroups, nil
+}
+
 // GetProcID implements Proc.
 func (p *proccache) GetProcID() (ID, error) {
 	if p.procid == nil {
@@ -367,6 +381,19 @@ func (p *proccache) GetStatic() (Static, error) {
 		return Static{}, err
 	}
 
+	// /proc/<pid>/cgroup(s) is normally world-readable.
+	// However cgroups aren't always supported -> return an empty array in that
+	// case.
+	cgroups, err := p.getCgroups()
+	var cgroupsStr []string
+	if err != nil {
+		cgroupsStr = []string{}
+	} else {
+		for _, c := range cgroups {
+			cgroupsStr = append(cgroupsStr, c.Path)
+		}
+	}
+
 	effectiveUID, err := strconv.ParseInt(status.UIDs[1], 10, 64)
 	if err != nil {
 		return Static{}, err
@@ -375,6 +402,7 @@ func (p *proccache) GetStatic() (Static, error) {
 	return Static{
 		Name:         stat.Comm,
 		Cmdline:      cmdline,
+		Cgroups:      cgroupsStr,
 		ParentPid:    stat.PPID,
 		StartTime:    startTime,
 		EffectiveUID: int(effectiveUID),

proc/read_test.go

@@ -63,6 +63,7 @@ func TestReadFixture(t *testing.T) {
 	wantstatic := Static{
 		Name:         "process-exporte",
 		Cmdline:      []string{"./process-exporter", "-procnames", "bash"},
+		Cgroups:      []string{"/system.slice/docker-8dde0b0d6e919baef8d635cd9399b22639ed1e400eaec1b1cb94ff3b216cf3c3.scope"},
 		ParentPid:    10884,
 		StartTime:    stime,
 		EffectiveUID: 1000,

proc/tracker.go

@@ -419,6 +419,7 @@ func (t *Tracker) Update(iter Iter) (CollectErrors, []Update, error) {
 		nacl := common.ProcAttributes{
 			Name:      idinfo.Name,
 			Cmdline:   idinfo.Cmdline,
+			Cgroups:   idinfo.Cgroups,
 			Username:  t.lookupUid(idinfo.EffectiveUID),
 			PID:       idinfo.Pid,
 			StartTime: idinfo.StartTime,