Scaling Vertically vs Scaling Horizontally

• May 13, 2025
• 2 Views
• By Patrick Chidera

As your backend application grows, one of the most important questions you’ll face is: how do I scale? If you’ve ever been confused by the terms “vertical scaling” and “horizontal scaling”, this post is for you.

What is Vertical Scaling?

Vertical scaling (also called scaling up) means adding more power to a single server. You're improving the server itself by:

• Upgrading the CPU (e.g., from 4-core to 16-core)
• Adding more RAM
• Using faster SSD storage

You're still using one machine—just a bigger, stronger one.

Pros:

• Simpler to implement
• No need to handle load balancing or distributed data

Cons:

• There’s a hardware limit—you can’t upgrade forever
• Single point of failure: if the server dies, everything dies

What is Horizontal Scaling?

Horizontal scaling (or scaling out) means adding more servers to your system.

Instead of upgrading one server, you use multiple smaller servers (nodes) that work together. This is common in cloud-native applications, distributed systems, and microservices architectures.

Pros:

• Can handle massive loads by distributing traffic
• Better fault tolerance (if one server crashes, others still run)

Cons:

• More complex architecture (load balancers, service discovery, etc.)
• Requires stateless design or session replication

Real-Life Example

Imagine you’re building a Backend-as-a-Service (BaaS) that supports real-time document updates via WebSocket.

• Vertical Scaling: You use a single big server with FastAPI and a lot of RAM to handle all WebSocket connections.
• Horizontal Scaling: You deploy 5 smaller FastAPI instances behind a load balancer, and use Redis pub/sub so they can all stay in sync when documents change.

When Should You Scale Vertically?

• You’re in early-stage development or MVP phase
• Your app has low to moderate traffic
• You want to keep infrastructure simple

When Should You Scale Horizontally?

• You expect high traffic and real-time demand
• You want high availability and fault tolerance
• Your app needs to run on multiple servers or in the cloud

Final Thoughts

There’s no one-size-fits-all answer. Most startups start with vertical scaling, and switch to horizontal scaling as demand grows.

The good news? Modern tools like Docker, Kubernetes, Redis, and cloud platforms (like AWS, GCP, DigitalOcean) make horizontal scaling more accessible than ever.

Start small. Scale smart.