Add monitor plugin loading

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

cmd/containerd/main.go

@@ -104,7 +104,11 @@ func main() {
 		if err := serveDebugAPI(); err != nil {
 			return err
 		}
-		runtimes, err := loadRuntimes()
+		monitor, err := loadMonitor()
+		if err != nil {
+			return err
+		}
+		runtimes, err := loadRuntimes(monitor)
 		if err != nil {
 			return err
 		}
@@ -237,7 +241,7 @@ func resolveContentStore() (*content.Store, error) {
 	return content.NewStore(cp)
 }
 
-func loadRuntimes() (map[string]containerd.Runtime, error) {
+func loadRuntimes(monitor plugin.ContainerMonitor) (map[string]containerd.Runtime, error) {
 	o := make(map[string]containerd.Runtime)
 	for name, rr := range plugin.Registrations() {
 		if rr.Type != plugin.RuntimePlugin {
@@ -248,6 +252,7 @@ func loadRuntimes() (map[string]containerd.Runtime, error) {
 			Root:    conf.Root,
 			State:   conf.State,
 			Context: log.WithModule(global, fmt.Sprintf("runtime-%s", name)),
+			Monitor: monitor,
 		}
 		if rr.Config != nil {
 			if err := conf.decodePlugin(name, rr.Config); err != nil {
@@ -264,6 +269,30 @@ func loadRuntimes() (map[string]containerd.Runtime, error) {
 	return o, nil
 }
 
+func loadMonitor() (plugin.ContainerMonitor, error) {
+	var monitors []plugin.ContainerMonitor
+	for name, m := range plugin.Registrations() {
+		if m.Type != plugin.ContainerMonitorPlugin {
+			continue
+		}
+		log.G(global).Infof("loading monitor plugin %q...", name)
+		ic := &plugin.InitContext{
+			Root:    conf.Root,
+			State:   conf.State,
+			Context: log.WithModule(global, fmt.Sprintf("monitor-%s", name)),
+		}
+		mm, err := m.Init(ic)
+		if err != nil {
+			return nil, err
+		}
+		monitors = append(monitors, mm.(plugin.ContainerMonitor))
+	}
+	if len(monitors) == 0 {
+		return plugin.NewNoopMonitor(), nil
+	}
+	return plugin.NewMultiContainerMonitor(monitors...), nil
+}
+
 func loadSnapshotter(store *content.Store) (snapshot.Snapshotter, error) {
 	for name, sr := range plugin.Registrations() {
 		if sr.Type != plugin.SnapshotPlugin {

container.go

@@ -32,7 +32,3 @@ type State interface {
 	// Pid is the main process id for the container
 	Pid() uint32
 }
-
-type ContainerMonitor interface {
-	Monitor(context.Context, Container) error
-}

plugin/monitor.go

@@ -0,0 +1,54 @@
+package plugin
+
+import "github.com/docker/containerd"
+
+// ContainerMonitor provides an interface for monitoring of containers within containerd
+type ContainerMonitor interface {
+	// Monitor adds the provided container to the monitor
+	Monitor(containerd.Container) error
+	// Stop stops and removes the provided container from the monitor
+	Stop(containerd.Container) error
+}
+
+func NewMultiContainerMonitor(monitors ...ContainerMonitor) ContainerMonitor {
+	return &multiContainerMonitor{
+		monitors: monitors,
+	}
+}
+
+func NewNoopMonitor() ContainerMonitor {
+	return &noopContainerMonitor{}
+}
+
+type noopContainerMonitor struct {
+}
+
+func (mm *noopContainerMonitor) Monitor(c containerd.Container) error {
+	return nil
+}
+
+func (mm *noopContainerMonitor) Stop(c containerd.Container) error {
+	return nil
+}
+
+type multiContainerMonitor struct {
+	monitors []ContainerMonitor
+}
+
+func (mm *multiContainerMonitor) Monitor(c containerd.Container) error {
+	for _, m := range mm.monitors {
+		if err := m.Monitor(c); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (mm *multiContainerMonitor) Stop(c containerd.Container) error {
+	for _, m := range mm.monitors {
+		if err := m.Stop(c); err != nil {
+			return err
+		}
+	}
+	return nil
+}

plugin/plugin.go

@@ -18,6 +18,7 @@ const (
 	RuntimePlugin PluginType = iota + 1
 	GRPCPlugin
 	SnapshotPlugin
+	ContainerMonitorPlugin
 )
 
 type Registration struct {
@@ -26,6 +27,7 @@ type Registration struct {
 	Init   func(*InitContext) (interface{}, error)
 }
 
+// TODO(@crosbymichael): how to we keep this struct from growing but support dependency injection for loaded plugins?
 type InitContext struct {
 	Root        string
 	State       string
@@ -34,6 +36,7 @@ type InitContext struct {
 	Snapshotter snapshot.Snapshotter
 	Config      interface{}
 	Context     context.Context
+	Monitor     ContainerMonitor
 }
 
 type Service interface {