Running a Local Mongo Replica Set

Contents

• What is it?
• Are there any prerequisites?
• How do I run the Replica Set?
• How do I access the Mongo Shells for each Instance?
• How does it work?
• Robo 3T
• Thanks / Further Reading

What is it?

This docker-compose setup starts a local mongo replica set with 3 instances running on:

• mongo1:30001
• mongo2:30002
• mongo3:30003

Are there any prerequisites?

• Docker Compose • Docker • The following in your /etc/hosts file:

127.0.0.1       mongo1
127.0.0.1       mongo2
127.0.0.1       mongo3

How do I run the Replica Set?

Simples:

docker-compose up -d

How do I access the Mongo Shells for each Instance?

docker exec -it mongo1 sh -c "mongo --port 30001"
docker exec -it mongo2 sh -c "mongo --port 30002"
docker exec -it mongo3 sh -c "mongo --port 30003"

How does it work?

• Starts three instances of Mongo
• On the first instance it runs the following Mongo Shell command:

rs.initiate(
  {
    _id : 'my-replica-set',
    members: [
      { _id : 0, host : "mongo1:30001" },
      { _id : 1, host : "mongo2:30002" },
      { _id : 2, host : "mongo3:30003" }
    ]
  }
)

• This causes all 3 instances to join the replica set named my-replica-set and start talking to each other
• One is elected to become the PRIMARY and the other two become SECONDARY instances
• The Docker healthcheck config is used to cause the initialisation of the replica set. More info in the further reading links.

Robo 3T

I used Robo 3T to test it locally and used the following config for the connection:

Thanks / Further Reading

• How to turn standalone MongoDB server into a replica set with Docker-Compose
• Creating a MongoDB replica set using Docker 🍃
• asoorm/docker-compose-mongo-replicaset.yml