This repository contains a Dockerfile to build a Docker image with an SSH
server. It's based on Alpine Linux and installs OpenSSH (sshd).
The Dockerfile creates an unprivileged user account with no password and no
shell. The username can be set by providing the build-arg USER when building
the image. The default is tunnel.
The SSH server needs to be configured with host keys before it'll start. The
host public keys and the authorized_keys file can be written either during
the build or at runtime. At runtime, the env var tunnel_authorized_keys will be
written to /home/tunnel/.ssh/authorized_keys.
Adding the private host keys to the built image would be insecure, so this image
grabs the host keys from the environment at runtime. The host keys are then
written to the appropriate files before the SSH server is started, eg. the env
var ssh_host_ed25519_key_pub will be written to /etc/ssh/ssh_host_ed25519_key.pub.