Data Durability in Replica Sets

Now that you are clear on how replication works and how it is implemented let’s look into some other details.

In one of the previous lessons, what happens when a primary node fails.

However, what happens if one of the secondary nodes is killed?

We learned previously that the goal of replication is to ensure that no data is lost if a server fails. Hence, the data is still available even if a secondary node is killed off.

Implementation

Now, let’s create a replica set, kill a secondary node, and then look at its impact on the data stored in the database.

Follow the steps below:

Creating a replica set

As in the previous lesson, the three mongod instances are initiated first.

The three commands, for running the mongod instances, have already been run for you in the terminal below.

To see the details of the commands used to run these mongod instances, go to the following lesson.

Starting the Mongo Shell

Next, connect to one of the running mongod processes using the MongoDB shell client.

Call mongo to connect to the mongod process that is running on port 27017.

Note: This will act as our primary node.

Type the command below on the terminal: