Mongo container with a replica set with only one node in docker-compose

Question

I want to create a Docker container with an instance of Mongo. In particular, I would like to create a replica set with only one node (since I'm interested in transactions and they are only available for replica sets).

Dockerfile

FROM mongo
RUN echo "rs.initiate();" > /docker-entrypoint-initdb.d/replica-init.js
CMD ["--replSet", "rs0"]

docker-compose.yml

version: "3"
services:
  db:
    build:
      dockerfile: Dockerfile
      context: .
    ports:
      - "27017:27017"

If I use the Dockerfile alone everything is fine, while if I use docker-compose it does not work: in fact if I then log to the container I got prompted as rs0:OTHER> instead of rs0:PRIMARY>.

I consulted these links but the solutions proposed are not working:

https://github.com/docker-library/mongo/issues/246#issuecomment-382072843 https://github.com/docker-library/mongo/issues/249#issuecomment-381786889

Answer 1

This is the compose file I have used for a while now for local development. You can remove the keyfile pieces if you don't need to connect via SSL.

version: "3.8"
services:
  mongodb:
    image : mongo:4
    container_name: mongodb
    hostname: mongodb
    restart: on-failure
    environment:
      - PUID=1000
      - PGID=1000
      - MONGO_INITDB_ROOT_USERNAME=mongo
      - MONGO_INITDB_ROOT_PASSWORD=mongo
      - MONGO_INITDB_DATABASE=my-service
      - MONGO_REPLICA_SET_NAME=rs0
    volumes:
      - mongodb4_data:/data/db
      - ./:/opt/keyfile/
    ports:
      - 27017:27017
    healthcheck:
      test: test $$(echo "rs.initiate().ok || rs.status().ok" | mongo -u $${MONGO_INITDB_ROOT_USERNAME} -p $${MONGO_INITDB_ROOT_PASSWORD} --quiet) -eq 1
      interval: 10s
      start_period: 30s
    command: "--bind_ip_all --keyFile /opt/keyfile/keyfile --replSet rs0"
volumes:
  mongodb4_data:

It uses Docker's health check (with a startup delay) to sneak in the rs.initiate() if it actually needs it after it's already running.

To create a keyfile.

Mac:

openssl rand -base64 741 > keyfile
chmod 600 keyfile

Linux:

openssl rand -base64 756 > keyfile
chmod 600 keyfile
sudo chown 999 keyfile
sudo chgrp 999 keyfile