Implement pre and post-update command execution.

actions/update.go

@@ -49,6 +49,19 @@ func Update(client container.Client, filter container.Filter, cleanup bool, noRe
 		}
 
 		if container.Stale {
+
+                        // Execute the pre-update command if it is defined.
+                        preUpdateCommandInfo, err := container.PreUpdateCommandInfo()
+                        if err != nil {
+                                log.Error("Error while reading pre-update command info.")
+                                log.Error(err)
+                        } else if preUpdateCommandInfo.IsDefined() {
+                                log.Info("Executing pre-update command.")
+		                if err := client.ExecuteCommand(container, preUpdateCommandInfo); err != nil {
+				        log.Error(err)
+			        }
+                        }
+
 			if err := client.StopContainer(container, timeout); err != nil {
 				log.Error(err)
 			}
@@ -72,6 +85,18 @@ func Update(client container.Client, filter container.Filter, cleanup bool, noRe
 			if !noRestart {
 				if err := client.StartContainer(container); err != nil {
 					log.Error(err)
+				} else {
+				        // Execute the post-update command if it is defined.
+                                        postUpdateCommandInfo, err := container.PostUpdateCommandInfo()
+                                        if err != nil {
+                                                 log.Error("Error while reading post-update command info.")
+                                                 log.Error(err)
+                                        } else if postUpdateCommandInfo.IsDefined() {
+                                                log.Info("Executing post-update command.")
+		                                if err := client.ExecuteCommand(container, postUpdateCommandInfo); err != nil {
+			                                log.Error(err)
+			                        }
+                                        }
 				}
 			}
 

container/client.go

@@ -25,6 +25,7 @@ type Client interface {
 	RenameContainer(Container, string) error
 	IsContainerStale(Container) (bool, error)
 	RemoveImage(Container) error
+	ExecuteCommand(Container, CommandInfo) error
 }
 
 // NewClient returns a new Client instance which can be used to interact with
@@ -222,6 +223,52 @@ func (client dockerClient) IsContainerStale(c Container) (bool, error) {
 	return false, nil
 }
 
+func (client dockerClient) ExecuteCommand(c Container, commandInfo CommandInfo) error {
+	bg := context.Background()
+
+        // Get the id of the actual container
+        containerJSON, err := client.api.ContainerInspect(bg, c.Name())
+        if err != nil {
+		return err
+	}
+	containerID := containerJSON.ID
+
+	// Create the exec
+	execConfig := types.ExecConfig{
+	        User: commandInfo.User,
+                Privileged: commandInfo.Privileged,
+                Tty: true,
+                AttachStderr: true,
+                AttachStdout: true,
+                Detach: false,
+                Env: commandInfo.Env,
+                Cmd: commandInfo.Cmd,
+	}
+	exec, err := client.api.ContainerExecCreate(bg, containerID, execConfig)
+	if err != nil {
+		return err
+	}
+
+	// Run the exec
+	execStartCheck := types.ExecStartCheck{Detach: false, Tty: true}
+	err = client.api.ContainerExecStart(bg, exec.ID, execStartCheck)
+	if err != nil {
+		return err
+	}
+
+        // Inspect the exec to get the exit code and print a message if the
+        // exit code is not success
+	execInspect, err := client.api.ContainerExecInspect(bg, exec.ID)
+        if err != nil {
+		return err
+	}
+        if execInspect.ExitCode > 0 {
+	        log.Error("Failed to execute command.")
+        }
+
+	return nil
+}
+
 func (client dockerClient) RemoveImage(c Container) error {
 	imageID := c.ImageID()
 	log.Infof("Removing image %s", imageID)

container/command_info.go

@@ -0,0 +1,27 @@
+package container
+
+import (
+        "encoding/json"
+)
+
+type CommandInfo struct {
+	User         string
+        Privileged   bool
+        Env          []string
+        Cmd          []string
+}
+
+func ReadCommandInfoFromJSON(commandInfoJSON string) (CommandInfo, error) {
+        commandInfo := CommandInfo{}
+
+        err := json.Unmarshal([]byte(commandInfoJSON), &commandInfo)
+        if err != nil {
+		return CommandInfo{}, err
+	}
+
+        return commandInfo, nil
+}
+
+func (commandInfo CommandInfo) IsDefined() bool {
+        return commandInfo.Cmd != nil && len(commandInfo.Cmd) > 0
+}

container/container.go

@@ -10,10 +10,12 @@ import (
 )
 
 const (
-	watchtowerLabel = "com.centurylinklabs.watchtower"
-	signalLabel     = "com.centurylinklabs.watchtower.stop-signal"
-	enableLabel     = "com.centurylinklabs.watchtower.enable"
-	zodiacLabel     = "com.centurylinklabs.zodiac.original-image"
+	watchtowerLabel        = "com.centurylinklabs.watchtower"
+	signalLabel            = "com.centurylinklabs.watchtower.stop-signal"
+	enableLabel            = "com.centurylinklabs.watchtower.enable"
+	zodiacLabel            = "com.centurylinklabs.zodiac.original-image"
+	preUpdateCommandLabel  = "com.centurylinklabs.watchtower.pre-update-command"
+	postUpdateCommandLabel = "com.centurylinklabs.watchtower.post-update-command"
 )
 
 // NewContainer returns a new Container instance instantiated with the
@@ -117,6 +119,36 @@ func (c Container) StopSignal() string {
 	return ""
 }
 
+// PreUpdateCommand returns the pre-update command set in the container's
+// metadata or an empty string if the user did not set it.
+func (c Container) PreUpdateCommandInfo() (CommandInfo, error) {
+	if val, ok := c.containerInfo.Config.Labels[preUpdateCommandLabel]; ok {
+
+		commandInfo, err := ReadCommandInfoFromJSON(val)
+                if err != nil {
+		        return CommandInfo{}, err
+	        }
+		return commandInfo, nil
+	}
+
+	return CommandInfo{}, nil
+}
+
+// PostUpdateCommand returns the post-update command set in the container's
+// metadata or an empty string if the user did not set it.
+func (c Container) PostUpdateCommandInfo() (CommandInfo, error) {
+	if val, ok := c.containerInfo.Config.Labels[postUpdateCommandLabel]; ok {
+
+		commandInfo, err := ReadCommandInfoFromJSON(val)
+                if err != nil {
+		        return CommandInfo{}, err
+	        }
+		return commandInfo, nil
+	}
+
+	return CommandInfo{}, nil
+}
+
 // Ideally, we'd just be able to take the ContainerConfig from the old container
 // and use it as the starting point for creating the new container; however,
 // the ContainerConfig that comes back from the Inspect call merges the default