If "serverless" is referring to AWS Lambda, Azure Functions, etc. then cost and scalability make it a great idea for some applications. If load varies by time, and there are surges and troughs, then running servers can cost more and potentially be less responsive to changing demand. Its a nice way to take load off a web server.
I feel like the use case is much smaller than the number of people preaching it warrants though.
You really have to have extremely unpredictable and spikey needs as well as need the processing immediately. Because if the traffic is predictable, you can schedule spot instances for much cheaper and same for if the data doesn't have to be processed immediately.
To me, the best use cases are very infrequent, spikey, brief needs. I haven't seen a lot of examples that meet that.
I agree. Where I saw it used, I'd say 99% of the application logic was in the web server, 1% in functions.
The 1% in functions was for processing large PDF files where users were sitting their looking at a progress bar waiting for the file to be processed in real time.
Another use case might be for something that is very low load, and say you have a lot of these services you may not want a VM for each one. However Docker provides a nicer solution for that: Get a VM (reserve if required) and run some kind of Docker host/orchestration on it, and run all your little services from there.
