[rodrigorcs]

This is incredibly generous context... thank you. A few of these hit close to problems I'm thinking about.

The Decider pattern you're describing (reading keys from memcache to decide behavior at runtime) is essentially what Openfuse is trying to productize. A centralized place that tells your fleet how to behave, without each process figuring it out independently. So it's validating to hear that's where Twitter landed organically.

On the PM2 point: you're right, holding a connection per process doesn't scale well at that huge scale. A local sidecar that receives state updates and exposes them via socket or shared memory to sibling processes is a much better model at that density. That's not how it works today, each process holds its own connection, but your framing is exactly how I'd want to evolve it. However, I can't say that is in the short-term goals for now, need to validate the product first and add some important features + publish the self hosted version.

On the dogpile: the half-open state is where this matters most. When a breaker opens and then transitions to half-open, you don't want 50 instances all sending probe requests simultaneously. The coalescing pattern you're describing from DataLoader is a neat way of solving it, I wonder if I can implement this somehow without adding a service/proxy closer to the clients just for that.

On failure modes: agreed, "service is down" is the simplest case. Catatonic connections, slow degradation, partial responses that look valid but aren't, those are harder to classify. Right now Openfuse trips on error rates, timeouts, and latency. However, the back-end is ready for custom metrics, I just didn't implement them yet. Having the breaker tripping based on OpenTelemetry metrics is also something I am looking forward to try, which opens a whole new world.

I'm not going to pretend this is built for Twitter-scale problems today. But hearing that the patterns you arrived at are directionally where this is headed is really encouraging.