Enable replication

Extends Install official release

Replication is used to shard one Mongo instance. It’s especially useful when working in bigger clusters.

It also is a requirement to use MongoDB Change Streams + SSE properly.

The following setup assumes you have a .env file looking smth like this:

UID=1000
GID=1000
  
MONGO_HOSTNAME=mongo
MONGO_PORT=27017
MONGO_USER=mongoapp
MONGO_PASSWORD=password

In order to enable replication, do the following:

1. Create a Keyfile, e.g. with openssl
2. Assign proper rights on the file

openssl rand -base64 756 > ./db/keys/replica_set_key
sudo chmod 400 ./db/keys/replica_set_key

3. Add the following to mongod.conf file:

security:
  authorization: enabled
  keyFile: /var/lib/mongo/keys/replica_set_key
  
replication:
  replSetName: "rs0"
  
net:
  bindIp: 0.0.0.0

4. Add the proper entrypoint, admin user and bind mounts to docker-compose.yml

mongo:
  image: mongo
  user: "${UID}:${GID}"
  hostname: $MONGO_HOSTNAME
  restart: always
  env_file:
    - ./.env
  environment:
    MONGO_INITDB_ROOT_USERNAME: $MONGO_USER
    MONGO_INITDB_ROOT_PASSWORD: $MONGO_PASSWORD
  ports:
    - "27017:27017"
  entrypoint: ["mongod", "--config", "/etc/mongod.conf"]
  
  volumes:
    - ./db/keys:/var/lib/mongo/keys
    - ./db/mongod.conf:/etc/mongod.conf
    - ./db/data:/data/db

5. Add a helper service to the docker compose file. It will activate

mongosetup:
  image: mongo
  depends_on:
    - mongo
  restart: "no"
  env_file:
    - ./.env
  entrypoint: [ "bash", "-c", "sleep 5 && mongosh --host mongo:27017 --username ${MONGO_USER} --password ${MONGO_PASSWORD} --eval 'rs.initiate()'"]