A Docker Compose file that spins up a MongoDB replica set with one master and two slave nodes.

.env

MONGODB_ROOT_USERNAME="YOUR_USERNAME_HERE"
MONGODB_ROOT_PASSWORD="YOUR_PASSWORD_HERE"

# Use `openssl rand -base64 756` to generate a valid MongoDB key.

MONGO_REPLICA_SET_KEY="YOUR_REPLICA_SET_KEY_HERE"

docker-compose.yml

name: mongodb_replica_set

services:
  master:
    image: mongo:latest
    command: mongod --port 27017 --replSet rs0 --bind_ip_all --keyFile /data/configdb/keyfile
    ports:
      - "27017:27017"
    extra_hosts:
      - "host.docker.internal:host-gateway"
    restart: unless-stopped
    environment:
      - MONGO_INITDB_ROOT_USERNAME=${MONGODB_ROOT_USERNAME}
      - MONGO_INITDB_ROOT_PASSWORD=${MONGODB_ROOT_PASSWORD}
      - MONGO_REPLICA_SET_KEY=${MONGO_REPLICA_SET_KEY}
    volumes:
      - ./keyfile.sh:/docker-entrypoint-initdb.d/keyfile.sh
      - master_data_db:/data
      - master_data_configdb:/data/configdb
    healthcheck:
      test: 'mongosh --quiet --port 27017 --eval "db.runCommand({ ping: 1 }).ok" | grep 1'
      interval: 5s

  slave_1:
    image: mongo:latest
    command: mongod --port 27018 --replSet rs0 --bind_ip_all --keyFile /data/configdb/keyfile
    ports:
      - "27018:27018"
    extra_hosts:
      - "host.docker.internal:host-gateway"
    restart: unless-stopped
    environment:
      - MONGO_REPLICA_SET_KEY=${MONGO_REPLICA_SET_KEY}
    volumes:
      - ./keyfile.sh:/docker-entrypoint-initdb.d/keyfile.sh
      - slave_1_data_db:/data
      - slave_1_data_configdb:/data/configdb
    healthcheck:
      test: 'mongosh --quiet --port 27018 --eval "db.runCommand({ ping: 1 }).ok" | grep 1'

  slave_2:
    image: mongo:latest
    command: mongod --port 27019 --replSet rs0 --bind_ip_all --keyFile /data/configdb/keyfile
    ports:
      - "27019:27019"
    extra_hosts:
      - "host.docker.internal:host-gateway"
    restart: unless-stopped
    environment:
      - MONGO_REPLICA_SET_KEY=${MONGO_REPLICA_SET_KEY}
    volumes:
      - ./keyfile.sh:/docker-entrypoint-initdb.d/keyfile.sh
      - slave_2_data_db:/data
      - slave_2_data_configdb:/data/configdb
    healthcheck:
      test: 'mongosh --quiet --port 27019 --eval "db.runCommand({ ping: 1 }).ok" | grep 1'

  init:
    image: mongo:latest
    restart: no
    extra_hosts:
      - "host.docker.internal:host-gateway"
    depends_on:
      master:
        condition: service_healthy
      slave_1:
        condition: service_healthy
      slave_2:
        condition: service_healthy
    command: >
      mongosh -u root -p root --host host.docker.internal --port 27017 --eval '
      rs.initiate({
        _id: "rs0",
        members: [
          { _id: 0, host: "host.docker.internal:27017" },
          { _id: 1, host: "host.docker.internal:27018" },
          { _id: 2, host: "host.docker.internal:27019" }
        ]
      })
      '

volumes:
  master_data_db:
  master_data_configdb:
  slave_1_data_db:
  slave_1_data_configdb:
  slave_2_data_db:
  slave_2_data_configdb:

networks:
  default:
    name: mongodb_replica_set_network

keyfile.sh

#!/bin/bash

# Echo MONGO_REPLICA_SET_KEY to the keyfile.

echo $MONGO_REPLICA_SET_KEY > /data/configdb/keyfile

# Change the permissions of the keyfile.

chmod 400 /data/configdb/keyfile

# Change the ownership of the keyfile.

chown mongodb:mongodb /data/configdb/keyfile