Added support to migrate containers

This commit adds an option to the checkpoint command to export a
checkpoint into a tar.gz file as well as importing a checkpoint tar.gz
file during restore. With all checkpoint artifacts in one file it is
possible to easily transfer a checkpoint and thus enabling container
migration in Podman. With the following steps it is possible to migrate
a running container from one system (source) to another (destination).

 Source system:
  * podman container checkpoint -l -e /tmp/checkpoint.tar.gz
  * scp /tmp/checkpoint.tar.gz destination:/tmp

 Destination system:
  * podman pull 'container-image-as-on-source-system'
  * podman container restore -i /tmp/checkpoint.tar.gz

The exported tar.gz file contains the checkpoint image as created by
CRIU and a few additional JSON files describing the state of the
checkpointed container.

Now the container is running on the destination system with the same
state just as during checkpointing. If the container is kept running
on the source system with the checkpoint flag '-R', the result will be
that the same container is running on two different hosts.

Signed-off-by: Adrian Reber <areber@redhat.com>

3 files changed, 112 insertions, 3 deletions

diff --git a/pkg/adapter/checkpoint_restore.go b/pkg/adapter/checkpoint_restore.go
new file mode 100644
index 000000000..9df1704ea
--- /dev/null
+++ b/pkg/adapter/checkpoint_restore.go
@@ -0,0 +1,99 @@
+// +build !remoteclient
+
+package adapter
+
+import (
+	"context"
+	"github.com/containers/libpod/libpod"
+	"github.com/containers/storage/pkg/archive"
+	jsoniter "github.com/json-iterator/go"
+	spec "github.com/opencontainers/runtime-spec/specs-go"
+	"github.com/pkg/errors"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+)
+
+// Prefixing the checkpoint/restore related functions with 'cr'
+
+// crImportFromJSON imports the JSON files stored in the exported
+// checkpoint tarball
+func crImportFromJSON(filePath string, v interface{}) error {
+	jsonFile, err := os.Open(filePath)
+	if err != nil {
+		return errors.Wrapf(err, "Failed to open container definition %s for restore", filePath)
+	}
+	defer jsonFile.Close()
+
+	content, err := ioutil.ReadAll(jsonFile)
+	if err != nil {
+		return errors.Wrapf(err, "Failed to read container definition %s for restore", filePath)
+	}
+	json := jsoniter.ConfigCompatibleWithStandardLibrary
+	if err = json.Unmarshal([]byte(content), v); err != nil {
+		return errors.Wrapf(err, "Failed to unmarshal container definition %s for restore", filePath)
+	}
+
+	return nil
+}
+
+// crImportCheckpoint it the function which imports the information
+// from checkpoint tarball and re-creates the container from that information
+func crImportCheckpoint(ctx context.Context, runtime *libpod.Runtime, input string) ([]*libpod.Container, error) {
+	// First get the container definition from the
+	// tarball to a temporary directory
+	archiveFile, err := os.Open(input)
+	if err != nil {
+		return nil, errors.Wrapf(err, "Failed to open checkpoint archive %s for import", input)
+	}
+	defer archiveFile.Close()
+	options := &archive.TarOptions{
+		// Here we only need the files config.dump and spec.dump
+		ExcludePatterns: []string{
+			"checkpoint",
+			"artifacts",
+			"ctr.log",
+			"network.status",
+		},
+	}
+	dir, err := ioutil.TempDir("", "checkpoint")
+	if err != nil {
+		return nil, err
+	}
+	defer os.RemoveAll(dir)
+	err = archive.Untar(archiveFile, dir, options)
+	if err != nil {
+		return nil, errors.Wrapf(err, "Unpacking of checkpoint archive %s failed", input)
+	}
+
+	// Load spec.dump from temporary directory
+	spec := new(spec.Spec)
+	if err := crImportFromJSON(filepath.Join(dir, "spec.dump"), spec); err != nil {
+		return nil, err
+	}
+
+	// Load config.dump from temporary directory
+	config := new(libpod.ContainerConfig)
+	if err = crImportFromJSON(filepath.Join(dir, "config.dump"), config); err != nil {
+		return nil, err
+	}
+
+	// This should not happen as checkpoints with these options are not exported.
+	if (len(config.Dependencies) > 0) || (len(config.NamedVolumes) > 0) {
+		return nil, errors.Errorf("Cannot import checkpoints of containers with named volumes or dependencies")
+	}
+
+	// Now create a new container from the just loaded information
+	container, err := runtime.RestoreContainer(ctx, spec, config)
+	if err != nil {
+		return nil, err
+	}
+
+	var containers []*libpod.Container
+	if container == nil {
+		return nil, nil
+	}
+
+	containers = append(containers, container)
+	return containers, nil
+}
diff --git a/pkg/adapter/containers.go b/pkg/adapter/containers.go
index 34ee70d3d..b7f4c272b 100644
--- a/pkg/adapter/containers.go
+++ b/pkg/adapter/containers.go
@@ -526,7 +526,7 @@ func (r *LocalRuntime) Checkpoint(c *cliconfig.CheckpointValues, options libpod.
 }
 
 // Restore one or more containers
-func (r *LocalRuntime) Restore(c *cliconfig.RestoreValues, options libpod.ContainerCheckpointOptions) error {
+func (r *LocalRuntime) Restore(ctx context.Context, c *cliconfig.RestoreValues, options libpod.ContainerCheckpointOptions) error {
 	var (
 		containers     []*libpod.Container
 		err, lastError error
@@ -538,7 +538,9 @@ func (r *LocalRuntime) Restore(c *cliconfig.RestoreValues, options libpod.Contai
 		return state == libpod.ContainerStateExited
 	})
 
-	if c.All {
+	if c.Import != "" {
+		containers, err = crImportCheckpoint(ctx, r.Runtime, c.Import)
+	} else if c.All {
 		containers, err = r.GetContainers(filterFuncs...)
 	} else {
 		containers, err = shortcuts.GetContainersByContext(false, c.Latest, c.InputArgs, r.Runtime)
diff --git a/pkg/adapter/containers_remote.go b/pkg/adapter/containers_remote.go
index bc6a9cfcd..776fcbb70 100644
--- a/pkg/adapter/containers_remote.go
+++ b/pkg/adapter/containers_remote.go
@@ -664,6 +664,10 @@ func (r *LocalRuntime) Attach(ctx context.Context, c *cliconfig.AttachValues) er
 
 // Checkpoint one or more containers
 func (r *LocalRuntime) Checkpoint(c *cliconfig.CheckpointValues, options libpod.ContainerCheckpointOptions) error {
+	if c.Export != "" {
+		return errors.New("the remote client does not support exporting checkpoints")
+	}
+
 	var lastError error
 	ids, err := iopodman.GetContainersByContext().Call(r.Conn, c.All, c.Latest, c.InputArgs)
 	if err != nil {
@@ -699,7 +703,11 @@ func (r *LocalRuntime) Checkpoint(c *cliconfig.CheckpointValues, options libpod.
 }
 
 // Restore one or more containers
-func (r *LocalRuntime) Restore(c *cliconfig.RestoreValues, options libpod.ContainerCheckpointOptions) error {
+func (r *LocalRuntime) Restore(ctx context.Context, c *cliconfig.RestoreValues, options libpod.ContainerCheckpointOptions) error {
+	if c.Import != "" {
+		return errors.New("the remote client does not support importing checkpoints")
+	}
+
 	var lastError error
 	ids, err := iopodman.GetContainersByContext().Call(r.Conn, c.All, c.Latest, c.InputArgs)
 	if err != nil {