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>

containers/containers.go

@@ -0,0 +1,24 @@
+package containers
+
+import "context"
+
+// Container represents the set of data pinned by a container. Unless otherwise
+// noted, the resources here are considered in use by the container.
+//
+// The resources specified in this object are used to create tasks from the container.
+type Container struct {
+	ID      string
+	Labels  map[string]string
+	Image   string
+	Runtime string
+	Spec    []byte
+	RootFS  string
+}
+
+type Store interface {
+	Get(ctx context.Context, id string) (Container, error)
+	List(ctx context.Context, filter string) ([]Container, error)
+	Create(ctx context.Context, container Container) (Container, error)
+	Update(ctx context.Context, container Container) (Container, error)
+	Delete(ctx context.Context, id string) error
+}

containers/storage.go

@@ -0,0 +1,57 @@
+package containers
+
+import (
+	"context"
+
+	"github.com/boltdb/bolt"
+	"github.com/pkg/errors"
+)
+
+var (
+	ErrExists   = errors.New("images: exists")
+	ErrNotFound = errors.New("images: not found")
+)
+
+// IsNotFound returns true if the error is due to a missing image.
+func IsNotFound(err error) bool {
+	return errors.Cause(err) == ErrNotFound
+}
+
+func IsExists(err error) bool {
+	return errors.Cause(err) == ErrExists
+}
+
+var (
+	bucketKeyStorageVersion = []byte("v1")
+	bucketKeyContainers     = []byte("containers")
+)
+
+type storage struct {
+	tx *bolt.Tx
+}
+
+func NewStore(tx *bolt.Tx) Store {
+	return &storage{
+		tx: tx,
+	}
+}
+
+func (s *storage) Get(ctx context.Context, id string) (Container, error) {
+	panic("not implemented")
+}
+
+func (s *storage) List(ctx context.Context, filter string) ([]Container, error) {
+	panic("not implemented")
+}
+
+func (s *storage) Create(ctx context.Context, container Container) (Container, error) {
+	panic("not implemented")
+}
+
+func (s *storage) Update(ctx context.Context, container Container) (Container, error) {
+	panic("not implemented")
+}
+
+func (s *storage) Delete(ctx context.Context, id string) error {
+	panic("not implemented")
+}