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Deploy replica set mongodb docker

Basically, we are going to have three containers, which are all inside their own Docker container network.

Let’s name them mongo1, mongo2, and mongo3. These are three Mongo instances of our replica set.

We are also going to expose each of them to our local machine, so that we can access them using the Mongo shell interface from our local machine.

Each of the three Mongo containers should be able to communicate with all other containers in the network.Advertisements

Creating a New Network

To see all networks currently on your system, run the command

$ docker network ls
NETWORK ID          NAME                DRIVER              SCOPE
2a4e341c6039        bridge              bridge              local
4fbef5286425        host                host                local
8062e4e7cdca        none                null                local

We will be adding a new network called my-mongo-cluster :

$ docker network create my-mongo-cluster

The new network should now be added to your list of networks :

$ docker network ls
NETWORK ID          NAME                DRIVER              SCOPE
2a4e341c6039        bridge              bridge              local
4fbef5286425        host                host                local
f65e93c94e42        mongo-cluster       bridge              local
8062e4e7cdca        none                null                local

Setting up Our Containers

To start up our first container, mongo1 run the command:

$ docker run \
-p 30001:27017 \
--name mongo1 \
--net my-mongo-cluster \
mongo mongod --replSet my-mongo-set

Let’s see what each part of this command does :

• docker run : Start a container from an imageAdvertisements
• -p 30001:27017 : Expose port 27017 in our container, as port 30001 on the localhost
• --name mongo1 : name this container “mongo1”
• --net my-mongo-cluster : Add this container to the “my-mongo-cluster” network.
• mongo : the name of the image we are using to spawn this container
• mongod --replSet my-mongo-set : Run mongod while adding this mongod instance to the replica set named “my-mongo-set”

Set up the other 2 containers by running :

$ docker run \
-p 30002:27017 \
--name mongo2 \
--net my-mongo-cluster \
mongo mongod --replSet my-mongo-set

$ docker run \
-p 30003:27017 \
--name mongo3 \
--net my-mongo-cluster \
mongo mongod --replSet my-mongo-set

Configuring Database Replication

Now that we have all our Mongo instances up and running, let’s add them to a replica set.

Connect to the Mongo shell in any of the containers.

docker exec -it mongo1 mongo

This command will open up the Mongo shell in our running mongo1 container (but you can also run it from the mongo2 or mongo3 container as well).

Inside the Mongo shell, we first create our configuration :

MongoDB shell version v5.0.8
> db = (new Mongo('localhost:27017')).getDB('test')
test
> config = {
  	"_id" : "my-mongo-set",
  	"members" : [
  		{
  			"_id" : 0,
  			"host" : "mongo1:27017"
  		},
  		{
  			"_id" : 1,
  			"host" : "mongo2:27017"
  		},
  		{
  			"_id" : 2,
  			"host" : "mongo3:27017"
  		}
  	]
  }

The first _id key in the config, should be the same as the --replSet flag which was set for our mongod instances, which is my-mongo-set in our case. We then list all the members we want in our replica set.

Since we added all our Mongo instances to our docker network. Their name in each container resolver to their respective IP addresses in the my-mongo-cluster network.

Finally, start the replica set by running the following command in the Mongo shell:

> rs.initiate(config)
{ "ok" : 1 }

If the command succeeds, your prompt should change to reflect that the current database is part of a replice set:

my-mongo-set:PRIMARY>

This means that the shell is currently associated with the PRIMARY database in our my-mongo-set cluster.

Let’s play around with our new replica set to make sure it works as intended. (I am omitting the my-mongo-set:PRIMARY> prompt for readability)

First, let’s insert a document into our primary database :

> db.mycollection.insert({name : 'sample'})
WriteResult({ "nInserted" : 1 })
> db.mycollection.find()
{ "_id" : ObjectId("57761827767433de37ff95ee"), "name" : "sample" }

We then make a new connection to one of our secondary databases (located on mongo2) and check if our document has replicate:

> db2 = (new Mongo('mongo2:27017')).getDB('test')
test
> db2.setSecondaryOk()
> db2.mycollection.find()
{ "_id" : ObjectId("57761827767433de37ff95ee"), "name" : "sample" }

We run the db2.setSecondaryOk() command to let the shell know that we are intentionally querying a database that is not our primary.

Conclusion

To conclude, our Support Engineers demonstrated how to deploy replica set mongodb docker