Understanding Scaling in AWS: Vertical vs. Horizontal

Understanding Scaling in AWS: Vertical vs. Horizontal


Scaling is a basic part of cloud computing that helps control how well an application works and if it's always available. In AWS, there are two main ways to scale: vertical scaling and horizontal scaling. Both methods have their own benefits and situations where they work best.

Vertical Scaling (Scaling Up)

Vertical scaling, or scaling up, involves increasing the capacity of an existing server or instance by adding more resources like CPU, RAM, or storage. It's like upgrading your computer to a stronger version. This method is simple and can work well for apps with scaling limits or databases that do better with a single-node structure.


Vertical scaling works well for apps with a single-node design or when you need stronger computing resources without making things more complicated. However, it has limits, mostly because of the server's hardware restrictions and possible downtime during upgrades.

Horizontal Scaling (Scaling Out)

Horizontal scaling, or scaling out, means adding more servers to your group to share the load better. This method lets the application handle more tasks by spreading them across many servers, instead of depending on just one server.


Horizontal scaling is preferred for apps that work in parallel or spread-out systems, like web apps and microservices. It makes it easy to manage more load by adding or taking away instances as needed. AWS services like Elastic Load Balancing and Auto Scaling make it simpler to share traffic and change the instance count.

Key Differences

  • Flexibility and Scalability: Horizontal scaling is more flexible and can manage growth better over time without being limited by server size.

  • Cost Implications: Vertical scaling can be simpler but may lead to higher costs when using more powerful (and expensive) instances. Horizontal scaling can be more cost-effective by using smaller, cheaper instances.

  • Complexity: Horizontal scaling makes the architecture more complex, needing methods for load balancing, session management, and possibly more advanced data management strategies.

  • Downtime: Vertical scaling might need downtime to upgrade to a bigger instance, while horizontal scaling can often be done without downtime.

Which to pick?

Horizontal scaling is preferred due to a couple of reasons:

  • Flexibility: It easily adjusts to changing demands by adding more instances.

  • Fault Tolerance: It improves reliability since the failure of one instance doesn't bring down the entire system.

  • Cost-Effectiveness: Pay only for extra resources when needed, aligning costs with actual usage.

  • Better Load Management: Distributes traffic across multiple instances, preventing any single point of overload or failure.