Add prometheus container level metrics

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

metrics/cgroups/cgroups.go

@@ -0,0 +1,70 @@
+package cgroups
+
+import (
+	"github.com/crosbymichael/cgroups"
+	"github.com/crosbymichael/cgroups/prometheus"
+	"github.com/docker/containerd"
+	"github.com/docker/containerd/plugin"
+	metrics "github.com/docker/go-metrics"
+	"golang.org/x/net/context"
+)
+
+const name = "cgroups"
+
+func init() {
+	plugin.Register(name, &plugin.Registration{
+		Type: plugin.ContainerMonitorPlugin,
+		Init: New,
+	})
+}
+
+func New(ic *plugin.InitContext) (interface{}, error) {
+	var (
+		ns        = metrics.NewNamespace("containerd", "container", nil)
+		collector = prometheus.New(ns)
+	)
+	oom, err := prometheus.NewOOMCollector(ns)
+	if err != nil {
+		return nil, err
+	}
+	metrics.Register(ns)
+	return &cgroupsMonitor{
+		collector: collector,
+		oom:       oom,
+		context:   ic.Context,
+	}, nil
+}
+
+type cgroupsMonitor struct {
+	collector *prometheus.Collector
+	oom       *prometheus.OOMCollector
+	context   context.Context
+}
+
+func (m *cgroupsMonitor) Monitor(c containerd.Container) error {
+	// skip non-linux containers
+	if _, ok := c.(containerd.LinuxContainer); !ok {
+		return nil
+	}
+	id := c.Info().ID
+	state, err := c.State(m.context)
+	if err != nil {
+		return err
+	}
+	cg, err := cgroups.Load(cgroups.V1, cgroups.PidPath(int(state.Pid())))
+	if err != nil {
+		return err
+	}
+	if err := m.collector.Add(id, cg); err != nil {
+		return err
+	}
+	return m.oom.Add(id, cg)
+}
+
+func (m *cgroupsMonitor) Stop(c containerd.Container) error {
+	if _, ok := c.(containerd.LinuxContainer); !ok {
+		return nil
+	}
+	m.collector.Remove(c.Info().ID)
+	return nil
+}