mongodb, replicates and error: { "$err" : "not master and slaveOk=false", "code" : 13435 }

📝🔥🤔 MongoDB Replication with Error: { "$err" : "not master and slaveOk=false", "code" : 13435 }

If you're new to MongoDB replication and you've encountered the error message "not master and slaveOk=false", don't worry, you're not alone! This error usually occurs when you try to perform a read operation on a secondary node that is not currently serving as the primary node. 🙅‍♂️🔐

Let's break down the problem and go through a step-by-step guide to help you understand and resolve it. 🚀💡

Understanding the Error

When you set up a MongoDB replica set, you have multiple nodes (instances) that act as a cluster. In this setup, one node is elected as the primary and the others are called secondaries. The primary node handles all write operations, while the secondaries replicate the data from the primary to serve read operations and provide redundancy. 👥💾

However, by default, MongoDB secondaries do not allow client applications to read from them. When you try to read from a secondary node without explicitly allowing it, you will encounter the "not master and slaveOk=false" error. 😱

Solution: Allowing Read Operations on Secondaries

To resolve this error and allow read operations on the secondary nodes, you need to follow these steps:

1. Connect to the primary node using the mongo shell or any MongoDB client.

2. Run the rs.slaveOk() command to allow read operations on the secondary nodes.

Example:

mongo --host Primary_IP_Address
rs.slaveOk()

After running this command, you should be able to perform read operations on the secondary nodes without encountering the error. You can now try running db.tt.find() on the secondary node, and it should return the expected results. 🎉

Verifying Successful Replication

To ensure that the replication is working correctly, you can monitor the replication status using the MongoDB ReplSet status page. Access it by navigating to:

http://<your_aws_instance_hostname>:28017/_replSet

On this status page, you should see the primary, secondary, and arbiter nodes listed, confirming that your replication setup is working as expected. 🔄🔎

Conclusion

MongoDB replication enables high availability and fault tolerance by synchronizing data across multiple nodes. However, accessing secondary nodes for read operations requires enabling the slaveOk() option explicitly. By following the steps outlined in this guide, you should be able to resolve the "not master and slaveOk=false" error and ensure smooth data replication across your MongoDB replica set. ✅🔄🗂

Now that you have a better understanding of MongoDB replication and how to handle common issues, go ahead and experiment with your setup. If you have any questions or encounter any challenges, feel free to leave a comment below. Happy replicating! 😊👍

Did you find this guide helpful? Share your experience with MongoDB replication in the comments below! 💬👇