api/services: define the container metadata service

Working from feedback on the existing implementation, we have now
introduced a central metadata object to represent the lifecycle and pin
the resources required to implement what people today know as
containers. This includes the runtime specification and the root
filesystem snapshots. We also allow arbitrary labeling of the container.
Such provisions will bring the containerd definition of container closer
to what is expected by users.

The objects that encompass today's ContainerService, centered around the
runtime, will be known as tasks. These tasks take on the existing
lifecycle behavior of containerd's containers, which means that they are
deleted when they exit. Largely, there are no other changes except for
naming.

The `Container` object will operate purely as a metadata object. No
runtime state will be held on `Container`. It only informs the execution
service on what is required for creating tasks and the resources in use
by that container. The resources referenced by that container will be
deleted when the container is deleted, if not in use. In this sense,
users can create, list, label and delete containers in a similar way as
they do with docker today, without the complexity of runtime locks that
plagues current implementations.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

plugin/container.go

@@ -2,15 +2,16 @@ package plugin
 
 import "context"
 
-type ContainerInfo struct {
-	ID      string
-	Runtime string
-	Spec    []byte
+type TaskInfo struct {
+	ID          string
+	ContainerID string
+	Runtime     string
+	Spec        []byte
 }
 
-type Container interface {
+type Task interface {
 	// Information of the container
-	Info() ContainerInfo
+	Info() TaskInfo
 	// Start the container's user defined process
 	Start(context.Context) error
 	// State returns the container's state

plugin/monitor.go

@@ -1,44 +1,44 @@
 package plugin
 
-// ContainerMonitor provides an interface for monitoring of containers within containerd
-type ContainerMonitor interface {
+// TaskMonitor provides an interface for monitoring of containers within containerd
+type TaskMonitor interface {
 	// Monitor adds the provided container to the monitor
-	Monitor(Container) error
+	Monitor(Task) error
 	// Stop stops and removes the provided container from the monitor
-	Stop(Container) error
+	Stop(Task) error
 	// Events emits events from the monitor
 	Events(chan<- *Event)
 }
 
-func NewMultiContainerMonitor(monitors ...ContainerMonitor) ContainerMonitor {
-	return &multiContainerMonitor{
+func NewMultiTaskMonitor(monitors ...TaskMonitor) TaskMonitor {
+	return &multiTaskMonitor{
 		monitors: monitors,
 	}
 }
 
-func NewNoopMonitor() ContainerMonitor {
-	return &noopContainerMonitor{}
+func NewNoopMonitor() TaskMonitor {
+	return &noopTaskMonitor{}
 }
 
-type noopContainerMonitor struct {
+type noopTaskMonitor struct {
 }
 
-func (mm *noopContainerMonitor) Monitor(c Container) error {
+func (mm *noopTaskMonitor) Monitor(c Task) error {
 	return nil
 }
 
-func (mm *noopContainerMonitor) Stop(c Container) error {
+func (mm *noopTaskMonitor) Stop(c Task) error {
 	return nil
 }
 
-func (mm *noopContainerMonitor) Events(events chan<- *Event) {
+func (mm *noopTaskMonitor) Events(events chan<- *Event) {
 }
 
-type multiContainerMonitor struct {
-	monitors []ContainerMonitor
+type multiTaskMonitor struct {
+	monitors []TaskMonitor
 }
 
-func (mm *multiContainerMonitor) Monitor(c Container) error {
+func (mm *multiTaskMonitor) Monitor(c Task) error {
 	for _, m := range mm.monitors {
 		if err := m.Monitor(c); err != nil {
 			return err
@@ -47,7 +47,7 @@ func (mm *multiContainerMonitor) Monitor(c Container) error {
 	return nil
 }
 
-func (mm *multiContainerMonitor) Stop(c Container) error {
+func (mm *multiTaskMonitor) Stop(c Task) error {
 	for _, m := range mm.monitors {
 		if err := m.Stop(c); err != nil {
 			return err
@@ -56,7 +56,7 @@ func (mm *multiContainerMonitor) Stop(c Container) error {
 	return nil
 }
 
-func (mm *multiContainerMonitor) Events(events chan<- *Event) {
+func (mm *multiTaskMonitor) Events(events chan<- *Event) {
 	for _, m := range mm.monitors {
 		m.Events(events)
 	}

plugin/plugin.go

@@ -18,7 +18,7 @@ const (
 	RuntimePlugin PluginType = iota + 1
 	GRPCPlugin
 	SnapshotPlugin
-	ContainerMonitorPlugin
+	TaskMonitorPlugin
 )
 
 type Registration struct {
@@ -37,7 +37,7 @@ type InitContext struct {
 	Snapshotter snapshot.Snapshotter
 	Config      interface{}
 	Context     context.Context
-	Monitor     ContainerMonitor
+	Monitor     TaskMonitor
 }
 
 type Service interface {

plugin/runtime.go

@@ -33,11 +33,11 @@ type Exit struct {
 // arch, or custom usage.
 type Runtime interface {
 	// Create creates a container with the provided id and options
-	Create(ctx context.Context, id string, opts CreateOpts) (Container, error)
+	Create(ctx context.Context, id string, opts CreateOpts) (Task, error)
 	// Containers returns all the current containers for the runtime
-	Containers(context.Context) ([]Container, error)
+	Tasks(context.Context) ([]Task, error)
 	// Delete removes the container in the runtime
-	Delete(context.Context, Container) (*Exit, error)
+	Delete(context.Context, Task) (*Exit, error)
 	// Events returns events for the runtime and all containers created by the runtime
 	Events(context.Context) <-chan *Event
 }