telemetry: add process collector for envoy (#1948)

* telemetry: add process collector for envoy

* add test

* maybe fix macos

* address comments

internal/telemetry/metrics/processes.go

@@ -0,0 +1,151 @@
+package metrics
+
+import (
+	"context"
+
+	"github.com/prometheus/procfs"
+	"go.opencensus.io/stats"
+	"go.opencensus.io/stats/view"
+)
+
+// A ProcessCollector collects stats about a process.
+type ProcessCollector struct {
+	cpuTotal  *stats.Float64Measure
+	openFDs   *stats.Int64Measure
+	maxFDs    *stats.Int64Measure
+	vsize     *stats.Int64Measure
+	maxVsize  *stats.Int64Measure
+	rss       *stats.Int64Measure
+	startTime *stats.Float64Measure
+	views     []*view.View
+}
+
+// NewProcessCollector creates a new ProcessCollector.
+func NewProcessCollector(name string) *ProcessCollector {
+	pc := &ProcessCollector{
+		cpuTotal: stats.Float64(
+			name+"_process_cpu_seconds_total",
+			"Total user and system CPU time spent in seconds.",
+			stats.UnitSeconds,
+		),
+		openFDs: stats.Int64(
+			name+"_process_open_fds",
+			"Number of open file descriptors.",
+			"{file_descriptor}",
+		),
+		maxFDs: stats.Int64(
+			name+"_process_max_fds",
+			"Maximum number of open file descriptors.",
+			"{file_descriptor}",
+		),
+		vsize: stats.Int64(
+			name+"_process_virtual_memory_bytes",
+			"Virtual memory size in bytes.",
+			stats.UnitBytes,
+		),
+		maxVsize: stats.Int64(
+			name+"_process_virtual_memory_max_bytes",
+			"Maximum amount of virtual memory available in bytes.",
+			stats.UnitBytes,
+		),
+		rss: stats.Int64(
+			name+"_process_resident_memory_bytes",
+			"Resident memory size in bytes.",
+			stats.UnitBytes,
+		),
+		startTime: stats.Float64(
+			name+"_process_start_time_seconds",
+			"Start time of the process since unix epoch in seconds.",
+			stats.UnitSeconds,
+		),
+	}
+	pc.views = []*view.View{
+		{
+			Name:        pc.cpuTotal.Name(),
+			Description: pc.cpuTotal.Description(),
+			Measure:     pc.cpuTotal,
+			Aggregation: view.Sum(),
+		},
+		{
+			Name:        pc.openFDs.Name(),
+			Description: pc.openFDs.Description(),
+			Measure:     pc.openFDs,
+			Aggregation: view.LastValue(),
+		},
+		{
+			Name:        pc.maxFDs.Name(),
+			Description: pc.maxFDs.Description(),
+			Measure:     pc.maxFDs,
+			Aggregation: view.LastValue(),
+		},
+		{
+			Name:        pc.vsize.Name(),
+			Description: pc.vsize.Description(),
+			Measure:     pc.vsize,
+			Aggregation: view.LastValue(),
+		},
+		{
+			Name:        pc.maxVsize.Name(),
+			Description: pc.maxVsize.Description(),
+			Measure:     pc.maxVsize,
+			Aggregation: view.LastValue(),
+		},
+		{
+			Name:        pc.rss.Name(),
+			Description: pc.rss.Description(),
+			Measure:     pc.rss,
+			Aggregation: view.LastValue(),
+		},
+		{
+			Name:        pc.startTime.Name(),
+			Description: pc.startTime.Description(),
+			Measure:     pc.startTime,
+			Aggregation: view.LastValue(),
+		},
+	}
+	return pc
+}
+
+// Views returns the views for the process collector.
+func (pc *ProcessCollector) Views() []*view.View {
+	return pc.views
+}
+
+// Measure measures the stats for a process.
+func (pc *ProcessCollector) Measure(ctx context.Context, pid int) error {
+	proc, err := procfs.NewProc(pid)
+	if err != nil {
+		return err
+	}
+
+	procStat, err := proc.Stat()
+	if err != nil {
+		return err
+	}
+
+	procStartTime, err := procStat.StartTime()
+	if err != nil {
+		return err
+	}
+
+	procFDLen, err := proc.FileDescriptorsLen()
+	if err != nil {
+		return err
+	}
+
+	procLimits, err := proc.Limits()
+	if err != nil {
+		return err
+	}
+
+	stats.Record(ctx,
+		pc.cpuTotal.M(procStat.CPUTime()),
+		pc.openFDs.M(int64(procFDLen)),
+		pc.maxFDs.M(procLimits.OpenFiles),
+		pc.vsize.M(int64(procStat.VSize)),
+		pc.maxVsize.M(procLimits.AddressSpace),
+		pc.rss.M(int64(procStat.RSS)),
+		pc.startTime.M(procStartTime),
+	)
+	return nil
+}