Resource saturation is the most common reason for application failure. Often, you will encounter the issue where your applications start rejecting requests due to CPU, memory, or hard disk overload. Adding more resources is not always a straightforward task as you should have additional capacity available when needed.

In a traditional on-premises environment, you need to calculate server capacity based on the assumption in advance. Workload capacity prediction becomes more challenging for a business such as a shopping website and any online business. Online traffic is very unpredictable and fluctuates heavily driven by global trends. Usually, procuring hardware can take anywhere between 3 to 6 months, and it's tough to guess capacity in advance. Ordering excess hardware will incur an extra cost as a resource is sitting idle, and a lack of resources will cause the loss of business due to application unreliability.

You need an environment where you don't need to guess capacity, and your application can scale on-demand. A public cloud provider such as AWS provides Infrastructure-as-a-Service (IaaS), which facilitates the on-demand availability of resources. In the cloud, you can monitor system supply and demand. You can automate the addition or removal of resources as needed. It allows you to maintain the level of resources that will satisfy demand without over-provisioning or under-provisioning.