Any service with more than 400 users that want to run a batch process for each user in constant time with respect to number of users.
Right, how many of those do exist with an internal architecture that will fit the Lambda model?
I'm curious more generally why would somebody use Lambda at all? Surely its far more expensive than running on your own servers (or instances), no?
Lambda's billed in 100 millisecond increments. EC2 servers are billed in one hour increments. If you need short tasks that run in bursty workloads, Lambda's (potentially) a no-brainer.
Firebase users don't want to run their own servers.
Wouldn't this still require linear time to scan a database and map users to work?