Dockerfile

FROM ubuntu:18.04
RUN apt-get update
RUN apt-get install -y --no-install-recommends apt-utils
RUN apt-get install software-properties-common -y
RUN apt-add-repository ppa:bitcoin/bitcoin
RUN apt-get install bitcoind -y
ADD entrypoint.sh $HOME/entrypoint.sh

CMD ["./entrypoint.sh"]

entrypoint.sh

#!/bin/bash
mkdir regtest
cd regtest
mkdir node1 node2
echo -e "\nStarting both bitcoin nodes.\n"
bitcoind -regtest -port=1111 -datadir=/regtest/node1 -rpcport=1112 --daemon
bitcoind -regtest -port=2222 -datadir=/regtest/node2 -rpcport=2223 --daemon
echo -e "Created an bitcoin-cli alias for each node:"
echo -e "   node1: bitcoin-cli -regtest -datadir=/regtest/node1 -rpcport=1112"
echo -e "   node2: bitcoin-cli -regtest -datadir=/regtest/node1 -rpcport=1112\n"
echo -e "You can interact with both nodes via typing their alias followed by a bitcoind RPC-command."
echo -e "Example: node1 getblockchaininfo\n"
echo -e "(If the shell didn't open, make sure you started the container interactively: 'docker run -it imageName')."

# Create aliases for both nodes so it's more comfortable to make RPC calls.
# Example: node1 getblockchaininfo
function node1(){
    bitcoin-cli -regtest -datadir=/regtest/node1 -rpcport=1112 $@
}
function node2() {
    bitcoin-cli -regtest -datadir=/regtest/node2 -rpcport=2223 $@
}

export -f node1;
export -f node2;

/bin/bash "$@"