Recipe for SSH forwarding with dinghy (https://github.com/codekitchen/dinghy)

dinghy-connect.sh

function dinghy-connect {
    # Make sure SSH agent is running
    ssh-add -K

    # Make sure dinghy is up and running
    dinghy create 2> /dev/null || echo "dinghy VM already created"
    dinghy up     2> /dev/null || echo "dinghy VM already running"

    # Check if SSH forwarding is already in place
    DINGHY_SSH_SOCK=$(dinghy ssh find -type f /tmp/ssh-*/agent.* 2> /dev/null || echo "missing")
    if [ "$DINGHY_SSH_SOCK" = "missing" ]; then
        echo "starting SSH connection"
        # Cleanup dangling SSH connections (just in case)
        dinghy ssh 'sudo rm -rf /tmp/ssh-*'

        # Run an ssh connection:
        # - using an emulated terminal (-t)
        # - in the background (-fn)
        # - with ssh-agent forwarding (-A)
        dinghy ssh -tfnA 'while true; do sleep 1000; done'

        # Lookup the socket on the dinghy VM
        DINGHY_SSH_SOCK=$(dinghy ssh find /tmp/ssh-*/agent.*)
    else
        echo "existing SSH connection"
    fi

    export PROXY_SSH_AUTH_SOCK=$DINGHY_SSH_SOCK
    eval "$(dinghy env)"
    echo "dinghy ready!"
}

docker-compose.yml

version: '2'
services:
  bash:
    entrypoint: /bin/bash
    volumes:
      # SSH Forwarding (1/2)
      - $PROXY_SSH_AUTH_SOCK:/ssh-agent-sock
    environment:
      # SSH Forwarding (2/2)
      SSH_AUTH_SOCK: /ssh-agent-sock