Difference between Scale Up and Scale Out
Scaling up means using a more powerful single server to process workloads within its boundaries. Common targets for scaling up include CPU, network, and storage resources. The goal is to increase the resources available to your application to achieve or maintain adequate performance. In a hardware-centric world, this often means installing a larger hard drive or replacing the entire computer with a more powerful machine. Managing a non-cloud system can make the scaling-up process lengthy, taking weeks or months to request, purchase, install, and deploy new resources. Whether dealing with virtual or physical resources, the key point is moving from smaller resources to larger, more performant ones.
On the other hand, scaling out a microservices application is as simple as launching a new container running a web server and adding it to the load balancer pool. The idea behind scaling out is to add identical services to improve performance. Systems that support this model can also handle resource removal as the load decreases, allowing for greater adaptability in resource scaling. This flexibility lets you quickly add or remove services to meet changing demands, reducing costs by only using (and paying for) the resources needed at the moment.
Scale-out enables you to combine multiple machines into a virtual single machine with a larger memory pool than a scale-up environment would require. While scale-up achieves higher performance, it faces limitations due to relying on a single processor. The complexity of the architecture means that scale-up and scale-out do not perform linearly. For example, adding two machines won’t necessarily double the performance of a single machine. In a high-demand environment, combining two machines may not yield double the performance, but this trade-off is worthwhile for the architectural flexibility it offers.