#!/bin/bash

install() {
    # Install needed software once
    sudo apt -y install docker.io
    sudo groupadd docker
    sudo usermod -aG docker $USER
    # Logout and login if you were not in group 'docker' before
    docker run hello-world
}
setup() {
    # Configure the virtual servers
    mkdir -p my-ubuntu/ ssh/
    cp ~/.ssh/id_rsa.pub ssh/
    cat ssh/*.pub > my-ubuntu/authorized_keys
    cat >my-ubuntu/Dockerfile <<EOF
FROM ubuntu:bionic
RUN apt update && \
    apt install -y openssh-server
RUN mkdir /root/.ssh
COPY authorized_keys /root/.ssh/authorized_keys
# run blocking command which prevents container to exit immediately after start. 
CMD service ssh start && tail -f /dev/null
EOF
    docker build my-ubuntu -t my-ubuntu
}
start() {
    testssh() {
	ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null root@"$1" echo "'$1'" '`uptime`'
    }
    export -f testssh
    # Start the virtual servers
    seq 100 |
	parallel -j0 'docker run -d --rm --name my-ubuntu-{} my-ubuntu; docker inspect my-ubuntu-{}' |
	# After this it is possible to do:
	#   ssh 10.0.0.99
	# from another physical server
	perl -nE '/"IPAddress": "(\S+)"/ and not $seen{$1}++ and say $1' |
	parallel testssh
    docker ps
}
stop() {
    # Stop the virtual servers
    # After there is no running processes on the host server
    # and after this it is no longer possible to do:
    #   ssh 10.0.0.99
    # from another physical server
    # The host server returns to the state before running `start`
    seq 100 | parallel -j0 docker stop my-ubuntu-{}
    docker ps
}
destroy() {
    # Remove the setup
    # After this the host server returns to the state before running `setup`
    rm -rf my-ubuntu/
    docker rmi my-ubuntu
}

full() {
    install
    setup
    start
    stop
    destroy
}