[ECS] [request]: Allow redirecting STDIN of a container

[kjkuan]

With docker it's possible to pipe data into a container like this:

$ (echo hello; echo world) | docker run -i ubuntu nl
     1  hello
     2  world
$

However, in ECS, even though it's possible to configure a container to be interactive in its task definition, doing so does not allow one to later pipe data to it. For example, this is possible with docker:

$ docker run --name nl -i ubuntu nl >/dev/null 2>&1 &
[2] 22254
$ (echo hello; echo world) | docker attach nl
     1  hello
     2  world
[2]+  Done                    docker run --name nl -i ubuntu nl > /dev/null 2>&1
$

But, if you have a container that's configured to be interactive (specifically, interactive is true and pseudoTerminal is false) via a task, you can not, later, on the host running the container, docker attach to its STDIN. Doing so blocks the docker attach command and would not return.

I suspect this is because the AttachStdin option in the create container API is not set to true when a container is created. In fact, docker inspect-ing the nl container in the above example, I see:

$ docker inspect nl | grep Attach
            "AttachStdin": true,
            "AttachStdout": true,
            "AttachStderr": true,

However, for a container started by ECS, I see:

            "AttachStdin": false,
            "AttachStdout": false,
            "AttachStderr": false,

Is there a plan to make these options (maybe the StdinOnce options as well) configurable in a ECS task definition? It would be very convenient for our tooling to be able to pipe data to an one-off container in ECS this way, to avoid having to re-build the docker image to include the data, or having to get the data over the network, in which case we probably have to upload them somewhere first.

Thank you

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[kjkuan]

As a work around, currently we use docker exec -i ... to feed the input data to a named pipe in the container. The container process will then redirect its STDIN from the named pipe.