Creating A MongoDB Replica Set Using Docker

A replica set in MongoDB is a group of database servers that maintain multiple copies of the same data. This helps in achieving redundancy and high availability of your data.

I will assume that you are already familiar with the following topics

Lets get started…

docker pull mongo

Create a custom virtual network in docker

Run the command given below to create a virtual network named mongodb-local-replicaset

docker network create mongodb-local-replicaset

Now lets decide upon the number of servers we would like to have in our replica set

Create 3 docker containers from the downloaded MongoDB image with each container representing a database server by running the commands given below.

docker run --name mongodb-local-1 --net mongodb-local-replicaset -d mongo --replSet "rs0"docker run --name mongodb-local-2 --net mongodb-local-replicaset -d mongo --replSet "rs0"docker run --name mongodb-local-3 --net mongodb-local-replicaset -d mongo --replSet "rs0"

The above commands create 3 MongoDB servers named mongodb-local-1,2 and 3.

It attaches them to the custom virtual network called mongodb-local-replicaset which we created earlier and sets the name of the replica set that each server is going to be a part of by passing it as an argument to the docker image name — mongo (the docker image is configured to pass in the argument to the mongod server process)

We should now have 3 containers running MongoDB servers in the background named mongodb-local-1, mongodb-local-2 and mongodb-local-3. Verify it by running the command given below.

docker ps -a

Time to initialize the replica set

Run the command given below to connect to the MongoDB server present within the container using the mongo client executable.

docker exec -it mongodb-local-1 mongo

This will create a client connection to the mongodb-local-1 server.

Now lets initiate the replica set specifying all the members by running the command given below

rs.initiate({ _id: "rs0", members: [{_id: 0, host: "mongodb-local-1:27017" }, {_id: 1, host: "mongodb-local-2:27017" },{_id: 2, host: "mongodb-local-3:27017" }]})

This will initiate the replica set with the value of _id as the same replica set name which we had given earlier while creating the containers and members containing the names of all the 3 containers along with the default port — 27017 on which the MongoDB server listens for client connections.

On successful execution, the above command gives the following output which indicates that the replica set is created successfully.

"ok" : 1,
"$clusterTime" : {
"clusterTime" : Timestamp(1615043092, 1),
"signature" : {
"keyId" : NumberLong(0)
"operationTime" : Timestamp(1615043092, 1)

To get more details on the replica set created, run the following commands and check the output.

// To get the entire configuration data of the replica set
// To get the current status of the replica set

Hope you enjoyed reading this and were able to create a replica set by following all the steps mentioned in the article. Feel free to comment in case your stuck or have any doubts and I’ll be happy to help. Cheers! :)

Further Reading

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