Comparison with PaaS

Given that serverless applications or FaaS applications do tend to be similar to The Twelve-Factor applications, people often compare them to PaaS offerings. However, if you look closely, PaaS offerings are not built to bring your entire application up and down for every request, but FaaS or serverless applications are built to do that. For example, if you look at a popular PaaS offering from AWS,  AWS Elastic Beanstalk, it is not designed to bring up the entire infrastructure every time a request is processed. However, it does provide lots of capabilities to the developers, where it makes the deployment and management of web applications very easy. 

The other key difference between PaaS and FaaS is scaling. With PaaS offerings, you still need a solution to handle the scaling of your application to the load. But with FaaS offerings, this is completely transparent. Lots of PaaS solutions, such as AWS Elastic Beanstalk, do offer autoscaling based on different parameters, such as CPU, memory, or network. However, this is still not tailored towards individual requests, which makes FaaS offerings much more efficient in scaling and provides best bang for buck in terms of cost.