How to Enable a Replica Set in MongoDB on Coolify (for Prisma ORM Compatibility)

Introduction

If you're using Prisma ORM with MongoDB, you may encounter an unexpected blocker: Prisma requires MongoDB to be part of a replica set — even if you're only running a single-node deployment. This requirement is non-negotiable, and without a replica set, Prisma simply won't work with MongoDB.

In this article, we’ll walk you through how to enable a single-node replica set on a MongoDB instance hosted via Coolify on your VPS. This is the simplest workaround for Prisma’s replica set dependency when you're not running a full production-ready MongoDB cluster.

Why Prisma Requires a Replica Set

Prisma uses features like transactions and change streams, which require MongoDB to be deployed as a replica set — even if you’re using just one node. This doesn’t mean you have to set up multiple MongoDB instances; you can configure a replica set on a single-node MongoDB server to satisfy Prisma’s requirements.

Prerequisites

• Coolify is already installed (see this tutorial)
• You've deployed a MongoDB database
• Your app uses Prisma

Step 1 - Access Your Coolify Dashboard

Log into your Coolify instance.

You should have a project with a MongoDB resource and a server where Coolify is running on.

Step 2 - Generate a Secure Keyfile

The replica set requires a shared keyfile for internal authentication, even if it's just one node.

1. In the dashboard, select the server where Coolify itself is running.

2. Switch to the terminal tab.

3. Run the following command to generate a 741-byte base64 key:

   openssl rand -base64 741

4. Create a new file:

   nano keyfile-mongo

5. Paste the generated key and save the file.

6. Secure the keyfile with proper permissions:

   chmod 400 keyfile-mongo
   chown 999:999 keyfile-mongo

7. Create a directory to store the keyfile and move it there:

   mkdir -p /root/replica
   mv keyfile-mongo /root/replica/replica.key

Step 3 - Mount the Keyfile in Your MongoDB Instance

1. In the Coolify dashboard, select the project with MongoDB and open your MongoDB instance.

2. Go to Persistent Storage.

3. Click + Add to add a new volume:

   • Name: replica
   • Source Path: /root/replica
   • Destination Path: /tmp/mongodb

This mounts your keyfile inside the MongoDB container.

Step 4 - Update the MongoDB Configuration

1. Go to the General tab for your MongoDB instance.

2. Scroll down to Custom MongoDB Configuration, and enter:

   replication:
     replSetName: "rs0"
   security:
     authorization: enabled
     keyFile: /tmp/mongodb/replica.key

   

Step 5 - Enable Replica Set Initialization

1. Start your MongoDB instance.

2. Go to the Terminal tab for your MongoDB instance.

3. Connect to the MongoDB server:

   mongosh -u root -p <mongodb_password> --authenticationDatabase admin

4. Now run:

   Replace 27017 with the port of your MongoDB instance.

   rs.initiate({
     _id: "rs0",
     members: [{ _id: 0, host: "localhost:27017" }],
   });

5. Save and restart your MongoDB service.

Step 6 - Testing the Setup

After restarting MongoDB:

1. Connect to the MongoDB server:

   mongosh -u root -p <mongodb_password> --authenticationDatabase admin

2. Run:

   rs.status();

3. Confirm that the replica set is active.

4. Test your Prisma application to ensure the connection works.

Step 7 - Production Considerations (Optional)

This tutorial sets up a single-node replica set to satisfy Prisma’s requirements. For high availability and production-grade environments, consider setting up a three-node replica set across separate containers or servers.

Conclusion

You've now configured MongoDB with a single-node replica set in Coolify, ensuring full compatibility with Prisma ORM — without the complexity of managing multiple MongoDB instances. This setup is ideal for local development, staging, or lightweight production use cases.

When you're ready to scale, transitioning to a true multi-node replica set will be straightforward.

License: MIT