Handle container links

Ensures that linked containers are restarted if any of their
dependencies are restarted -- and makes sure that everything happens in
the correct order.

docker/client.go

@@ -0,0 +1,116 @@
+package docker
+
+import (
+	"log"
+
+	"github.com/samalba/dockerclient"
+)
+
+var (
+	pullImages bool
+)
+
+func init() {
+	pullImages = true
+}
+
+type Client interface {
+	ListContainers() ([]Container, error)
+	RefreshImage(container *Container) error
+	Stop(container Container) error
+	Start(container Container) error
+}
+
+func NewClient() Client {
+	docker, err := dockerclient.NewDockerClient("unix:///var/run/docker.sock", nil)
+
+	if err != nil {
+		log.Fatalf("Error instantiating Docker client: %s\n", err)
+	}
+
+	return DockerClient{api: docker}
+}
+
+type DockerClient struct {
+	api dockerclient.Client
+}
+
+func (client DockerClient) ListContainers() ([]Container, error) {
+	cs := []Container{}
+
+	runningContainers, err := client.api.ListContainers(false, false, "")
+	if err != nil {
+		return nil, err
+	}
+
+	for _, runningContainer := range runningContainers {
+		containerInfo, err := client.api.InspectContainer(runningContainer.Id)
+		if err != nil {
+			return nil, err
+		}
+
+		imageInfo, err := client.api.InspectImage(containerInfo.Image)
+		if err != nil {
+			return nil, err
+		}
+
+		cs = append(cs, Container{containerInfo: containerInfo, imageInfo: imageInfo})
+	}
+
+	return cs, nil
+}
+
+func (client DockerClient) RefreshImage(c *Container) error {
+	containerInfo := c.containerInfo
+	oldImageInfo := c.imageInfo
+	imageName := containerInfo.Config.Image
+
+	if pullImages {
+		log.Printf("Pulling %s for %s\n", imageName, c.Name())
+		if err := client.api.PullImage(imageName, nil); err != nil {
+			return err
+		}
+	}
+
+	newImageInfo, err := client.api.InspectImage(imageName)
+	if err != nil {
+		return err
+	}
+
+	if newImageInfo.Id != oldImageInfo.Id {
+		log.Printf("Found new %s image (%s)\n", imageName, newImageInfo.Id)
+		c.Stale = true
+	}
+
+	return nil
+}
+
+func (client DockerClient) Stop(c Container) error {
+	signal := "SIGTERM"
+
+	if sig, ok := c.containerInfo.Config.Labels["com.centurylinklabs.watchtower.stop-signal"]; ok {
+		signal = sig
+	}
+
+	log.Printf("Stopping: %s\n", c.Name())
+
+	if err := client.api.KillContainer(c.containerInfo.Id, signal); err != nil {
+		return err
+	}
+
+	return client.api.RemoveContainer(c.containerInfo.Id, true, false)
+}
+
+func (client DockerClient) Start(c Container) error {
+	config := c.runtimeConfig()
+	hostConfig := c.hostConfig()
+
+	log.Printf("Starting: %s\n", c.Name())
+
+	newContainerId, err := client.api.CreateContainer(config, c.Name())
+	if err != nil {
+		return err
+	}
+
+	return client.api.StartContainer(newContainerId, hostConfig)
+}