AttachStdout not working in StartContainer

[ebuchman]

I have an existing data-container. I'd like to create a new container with volumes from the data-container and stomp around in it interactively, or at the very least run a command and get to see Stdout. Unfortunately attaching Stdout, or anything else I've tried, doesn't work. Some code:

         // vars that exist ...
        // var interactive bool
        // var args []string
        // var DockerClient *docker.Client
        volumesFrom := "existing_data_container"
        opts := docker.CreateContainerOptions{
                Name: "exec_" + volumesFrom,
                Config: &docker.Config{
                        Image:        "myimage",
                        User:         "root",
                        AttachStdout: true,
                        AttachStderr:    true,
                        NetworkDisabled: true,
                },
                HostConfig: &docker.HostConfig{
                        VolumesFrom: []string{volumesFrom},
                },
        }
        if interactive {
                opts.Config.AttachStdin = true
                opts.Config.OpenStdin = true
                opts.Config.Cmd = []string{"/bin/bash"}
        } else {
                opts.Config.Cmd = args
        }
        cont, err := DockerClient.CreateContainer(opts)
        if err != nil {
                return err 
        }   
        id_main := cont.ID
        logger.Infoln("Data Container ID: " + id_main)

        // start the container
        if err := DockerClient.StartContainer(id, opts.HostConfig); err != nil {
                return err 
        }   

        logger.Infof("Waiting for %s to exit so we can remove the container\n", id_main)
        if err := waitContainer(id_main); err != nil {
                return err 
        }   

        logger.Infof("Removing container %s\n", id_main)
        if err := removeContainer(id_main); err != nil {
                return err 
        }   
        return nil 

If I pass some command, say args = []string{"ls"}, I get something like:

Data Container ID: cb9913cd3d89bd8a303475acf96c6f83cdbae01e40da6b5d9c9c218aa6101575
Waiting for cb9913cd3d89bd8a303475acf96c6f83cdbae01e40da6b5d9c9c218aa6101575 to exit so we can remove the container
Removing container cb9913cd3d89bd8a303475acf96c6f83cdbae01e40da6b5d9c9c218aa6101575

So it works but no output from ls.

If I avoid removing the container and check docker logs, the output of ls is there and correct, but it doesn't make it to my terminal's stdout. And if I try to do the interactive thing, it just hangs.

Of course it works just fine from the cli:

docker run --volumes-from existing_data_container myimage ls

Any idea what I'm doing wrong?

[pwaller]

Hi @ebuchman. You also have to attach to the container to obtain the stream, and copy that to os.Stdout, something like this: https://gist.github.com/pwaller/314c7591a8bfd32f8999#file-dockerclient-bug-go-L60

I think the bug here is that the documentation is possibly not clear enough as to what the meaning of AttachStdout is. For that you have to look at for the docker docs themselves, but those aren't very clear either: http://docs.docker.com/engine/reference/api/docker_remote_api_v1.20/#create-a-container. It just says "Attaches stdout" which I take to mean "don't send stdout to /dev/null". To actually obtain the stream you need to run a separate attach command. Beware though, that this isn't easy!

[fsouza]

@pwaller thanks for helping him!

@ebuchman does it work for you?

Do you both think that improving the Docker would be enough here. Maybe providing a godoc example along with the field description?