Pay-per-use is one of the major drivers of serverless adoption. Small startups love it because their monthly bill is almost zero. Large organizations are attracted to improving their IT spending when the old servers have very low utilization and are mostly idle. While it sounds promising, it also produces a massive challenge – paying per use means that you don't know how much you are going to pay – why? Because most of us don't know exactly how much we are going to use. In addition, new and unique challenges arise – a bug in the code can suddenly lead to a very high cloud bill, as well as an external API that has a very slow response, causing us to pay for this additional time.