Cost model

Suppose that you have built an online store with serverless. The average user will make some requests to see a few products and a few more requests to decide whether they will buy something or not. In serverless, a single unit of code has a predictable time to execute for a given input. After collecting some data, you can predict how much a single user costs on average, and this unit cost will remain almost constant as your application grows in usage.

Knowing how much a single user costs and keeping this number fixed is very important for a startup. It helps to decide how much you need to charge for a service or earn through ads or sales to have a profit.

In a traditional infrastructure, you need to make payments in advance, and scaling your application means increasing your capacity in steps. So, calculating the unit cost of a user is a more difficult task and it's a variable number.

In the following diagram, the left-hand side shows traditional infrastructures with stepped costs and the right-hand side depicts serverless infrastructures with linear costs: