Set up MongoDB primary and secondary with Docker.

MongoDB is a popular choice for developers today when it comes to NoSQL databases. The MongoDB Community Edition is readily available as a Docker image.

To enable MongoDB transactional queries, you need to configure a replica set with primary and secondary database connections.

In this post, we’ll walk through how to set up MongoDB’s primary and secondary nodes and configure a replica set using a single docker-compose file.

Prerequisites for Running the Below docker-compose File

• Create a Docker Network

 docker network create dev_network

• Replica Set Configuration Script

Create a file named replicaset.sh under the scripts directory to configure the replica set:

scripts/replicaset.sh

	#!/bin/bash
	#MONGODB1=`ping -c 1 mongo1 | head -1 | cut -d "(" -f 2 | cut -d ")" -f 1`
	#MONGODB2=`ping -c 1 mongo2 | head -1 | cut -d "(" -f 2 | cut -d ")" -f 1`
	#MONGODB3=`ping -c 1 mongo3 | head -1 | cut -d "(" -f 2 | cut -d ")" -f 1`
	MONGODB1=primary
	MONGODB2=secondary1
	MONGODB3=secondary2
	echo "**********************************************" ${MONGODB1}
	echo "Waiting for startup.."
	until curl http://${MONGODB1}:27017/serverStatus\?text\=1 2>&1 | grep uptime | head -1; do
	printf '.'
	sleep 1
	done
	# echo curl http://${MONGODB1}:28017/serverStatus\?text\=1 2>&1 | grep uptime | head -1
	# echo "Started.."
	echo SETUP.sh time now: `date +"%T" `
	mongosh --host ${MONGODB1}:27017 <<EOF
	var cfg = {
	"_id": "rs0",
	"protocolVersion": 1,
	"version": 1,
	"members": [
	{
	"_id": 0,
	"host": "${MONGODB1}:27017",
	"priority": 2
	},
	{
	"_id": 1,
	"host": "${MONGODB2}:27017",
	"priority": 0
	},
	{
	"_id": 2,
	"host": "${MONGODB3}:27017",
	"priority": 0
	}
	],settings: {chainingAllowed: true}
	};
	rs.initiate(cfg, { force: true });
	rs.reconfig(cfg, { force: true });
	db.getMongo().setReadPref('nearest');
	db.getMongo().setSlaveOk();
	rs.secondaryOk();
	EOF

view raw replicaset.sh hosted with ❤ by GitHub

• Grant Permissions to the Script Ensure the script has execute permissions so Docker can access it:

 chmod +x scripts/replicaset.sh

• Update the Host File for Resolvers

Map the Mongo paths to localhost by editing the /etc/hosts file:

127.0.0.1   primary secondary1 secondary2 # mongo docker resolvers

• Create the Docker Compose File

Define your MongoDB configuration in a docker-compose.yml file:

	name: 'dev-services'
	version: "3.8"
	# refer https://dev.to/prakash_chokalingam/set-up-mongodb-primary-and-secondary-with-docker-7gn
	mongo-replica-setup:
	container_name: mongo-replica-setup
	image: mongo:latest
	restart: on-failure
	networks:
	- dev_network
	volumes:
	- ./scripts:/scripts
	entrypoint: [ "/scripts/replicaset.sh" ]
	depends_on:
	- mongo-primary
	- mongo-secondary1
	- mongo-secondary2
	mongo-primary:
	hostname: primary
	container_name: primarymongo
	image: mongo:latest
	networks:
	- dev_network
	expose:
	- 27017
	ports:
	- 27017:27017
	restart: always
	entrypoint: [ "/usr/bin/mongod", "--bind_ip_all", "--replSet", "rs0", "--dbpath", "/data/db" ]
	volumes:
	- ./volumes/mongo/primary/db:/data/db
	- ./volumes/mongo/primary/configdb:/data/configdb
	environment:
	- MONGO_INITDB_DATABASE=dbname
	mongo-secondary1:
	hostname: secondary1
	container_name: secondary1mongo
	image: mongo:latest
	networks:
	- dev_network
	expose:
	- 27017
	ports:
	- 27018:27017
	restart: always
	entrypoint: [ "/usr/bin/mongod", "--bind_ip_all", "--replSet", "rs0", "--dbpath", "/data/db"]
	volumes:
	- ./volumes/mongo/secondary1/db:/data/db
	- ./volumes/mongo/secondary1/configdb:/data/configdb
	# Arbiter
	mongo-secondary2:
	hostname: secondary2
	container_name: secondary2mongo
	image: mongo:latest
	networks:
	- dev_network
	expose:
	- 27017
	ports:
	- 27019:27017
	restart: always
	entrypoint: [ "/usr/bin/mongod", "--bind_ip_all", "--replSet", "rs0", "--dbpath", "/data/db" ]
	volumes:
	- ./volumes/mongo/secondary2/db:/data/db
	- ./volumes/mongo/secondary2/configdb:/data/configdb
	networks:
	dev_network:
	name: 'dev_network'
	external: true

view raw docker-compose.yml hosted with ❤ by GitHub

• Run the Docker Compose File Start the containers using the following command:

docker-compose up

🎉 That’s it! Your MongoDB primary and secondaries are up and running. The replica set is configured and ready to use.

Your MongoDB connection URL is:

mongodb://localhost:27020,localhost:27021,localhost:27022/dbname?replicaSet=rs0&retryWrites=true&w=majority