Originally published at blog.apario.net

When a containerised process needs input via stdin, delivering it from outside the container is often done in a more complex way than necessary. This article describes a lightweight, robust approach using a host-created FIFO mounted into the container, providing a simple, near-zero-overhead, atomic, scriptable, multi-source stdin channel with no extra daemons, no docker exec , and no PTY involvement.

The problem

Some processes use stdin as their primary input channel. When such a process runs inside a Docker container, the conventional options for sending input to it from the host are:

docker exec -i container command — spawns a new process inside the container rather than reaching the existing one's stdin, introduces extra pipes and process overhead, and is unsuitable for automation when ordering or atomicity matters.

docker attach , or docker run -i with a held-open stdin — attaches a stdin stream to the container's primary process, but is fragile, blocks the…