1. This doesn't work if you were actually trying to build your API as microservices. You might have 60+ functions, some which call each other, and keeping them all warm is not really a good option.
2. Keeping a minimum number of instances warm fails to account for half the point of using serverless architectures: being able to scale. Sure, if you have little to no traffic, you can keep a couple instances warm and be up, but if your app needs to scale to 5 or 10 or more instances to handle bursts of traffic, the surfers who hit that cold start end up dealing with an extremely bad experience.
More importantly, as Lambda gets more popular, uptime pingers get less and less useful because of tragedy of the commons. The reason for needing cold starts at all is that AWS is rotating out instances to be able to keep up with overall demand with limited resourcs. If only a few people are sending heartbeats to their instances, their instances stay in rotation because other people's get rotated out instead. If everyone is sending heartbeat requests, some of them will still end up getting rotated out, and therefore everyone will need to increase the frequency of the heartbeat requests to keep their functions warm. It's not a sustainable solution, and I'm baffled that AWS tacitly promotes it as a resolution to the problem they themselves have caused.
It's been years. AWS needs to fix Lambda VPC cold starts.
