MongoDB test replica set with a single container

mongo_rs.sh

#!/bin/zsh

# You will need a keyfile. This is how you generate one:
# `openssl rand -base64 756 > mgkey`
# It needs to have specific permissions, so `chmod 400 mgkey` it.

# Start the MongoDB container.
docker run \
   -d \
   --rm \
   --detach \
   --name mg \
   -p 27017:27017 \
   -e MONGO_INITDB_ROOT_USERNAME=<root> \
   -e MONGO_INITDB_ROOT_PASSWORD=<root password> \
   -v <path to keyfile>:/data/mgkey \
   -v <path to data dir>:/data/db \
mongo:4.4.1 mongod --port=27017 --replSet=my_repl_set --keyFile=/data/mgkey

# Wait for MongoDB to start.
sleep 3

# Tell MongoDB to initialise a replica set with localhost as the only member.
docker exec mg mongo -u <root> -p <root password> --port 27017 --eval "rs.initiate({_id: \"my_repl_set\", members: [{ _id: 0, host: \"localhost:27017\" }]})"