Add config option to disable cmdline cache for System Process Metrics…

…et (#3891)

Add the ability to disable the caching of the system process metricset's `system.process.cmdline` value. Some systems allow processes to update their command line so having these changes reflected in the MetricSet's data is desired.

The default behavior is caching enabled.

Closes #3799

CHANGELOG.asciidoc

@@ -114,6 +114,7 @@ https://github.com/elastic/beats/compare/v5.1.1...master[Check the HEAD diff]
 - Add the ability to collect the environment variables from system processes. {pull}3337[3337]
 - Add experimental metricset `perfmon` to Windows module. {pull}3758[3758]
 - Add memcached module with stats metricset. {pull}3693[3693]
+- Add the `process.cmdline.cache.enabled` config option to the System Process Metricset. {pull}3891[3891]
 
 *Packetbeat*
 - Add `fields` and `fields_under_root` to packetbeat protocols configurations. {pull}3518[3518]

metricbeat/metricbeat.full.yml

@@ -64,6 +64,9 @@ metricbeat.modules:
   # if true, exports the CPU usage in ticks, together with the percentage values
   #cpu_ticks: false
 
+  # If false, cmdline of a process is not cached.
+  #process.cmdline.cache.enabled: true
+
   # Enable collection of cgroup metrics from processes on Linux.
   #process.cgroups.enabled: true
 

metricbeat/module/system/_meta/config.full.yml

@@ -36,6 +36,9 @@
   # if true, exports the CPU usage in ticks, together with the percentage values
   #cpu_ticks: false
 
+  # If false, cmdline of a process is not cached.
+  #process.cmdline.cache.enabled: true
+
   # Enable collection of cgroup metrics from processes on Linux.
   #process.cgroups.enabled: true
 

metricbeat/module/system/process/_meta/docs.asciidoc

@@ -10,6 +10,14 @@ This metricset is available on:
 - Linux
 - Windows
 
+[float]
+=== Cache CmdLine
+
+This metricset caches the command line args for a running process. This means if you alter
+the command line for a process while this metricset is running, these changes are not detected.
+This feature can be disabled by adding
+`process.cmdline.cache.enabled: false` to the system module configuration.
+
 [float]
 === Control Group (cgroup) Metrics
 

metricbeat/module/system/process/helper.go

@@ -40,6 +40,7 @@ type ProcStats struct {
 	ProcsMap     ProcsMap
 	CpuTicks     bool
 	EnvWhitelist []string
+	CacheCmdLine bool
 
 	procRegexps []match.Matcher // List of regular expressions used to whitelist processes.
 	envRegexps  []match.Matcher // List of regular expressions used to whitelist env vars.
@@ -342,7 +343,9 @@ func (procStats *ProcStats) GetProcStats() ([]common.MapStr, error) {
 		var cmdline string
 		var env common.MapStr
 		if previousProc := procStats.ProcsMap[pid]; previousProc != nil {
-			cmdline = previousProc.CmdLine
+			if procStats.CacheCmdLine {
+				cmdline = previousProc.CmdLine
+			}
 			env = previousProc.Env
 		}
 

metricbeat/module/system/process/process.go

@@ -27,8 +27,9 @@ func init() {
 // MetricSet that fetches process metrics.
 type MetricSet struct {
 	mb.BaseMetricSet
-	stats  *ProcStats
-	cgroup *cgroup.Reader
+	stats        *ProcStats
+	cgroup       *cgroup.Reader
+	cacheCmdLine bool
 }
 
 // New creates and returns a new MetricSet.
@@ -38,8 +39,10 @@ func New(base mb.BaseMetricSet) (mb.MetricSet, error) {
 		Cgroups      *bool    `config:"process.cgroups.enabled"`
 		EnvWhitelist []string `config:"process.env.whitelist"`
 		CPUTicks     bool     `config:"cpu_ticks"`
+		CacheCmdLine bool     `config:"process.cmdline.cache.enabled"`
 	}{
-		Procs: []string{".*"}, // collect all processes by default
+		Procs:        []string{".*"}, // collect all processes by default
+		CacheCmdLine: true,
 	}
 	if err := base.Module().UnpackConfig(&config); err != nil {
 		return nil, err
@@ -51,6 +54,7 @@ func New(base mb.BaseMetricSet) (mb.MetricSet, error) {
 			Procs:        config.Procs,
 			EnvWhitelist: config.EnvWhitelist,
 			CpuTicks:     config.CPUTicks,
+			CacheCmdLine: config.CacheCmdLine,
 		},
 	}
 	err := m.stats.InitProcStats()