[toomuchtodo]

Do health checks work within a VPC? My understanding was they don't, so this only works for externally facing services.

I agree Haproxy is solid, but ELBs are wonderful for internal microservices.

If you do decide to use Haproxy for microservices internally, I highly recommend Synapse from AirBnB: https://github.com/airbnb/synapse

[frugalmail]

Ruby, High Availablity and High Scalability? Despite idempotency, I'm not sure how comfortable I am with that.

[mryan]

Synapse is a service discovery framework. Essentially, it just writes HAProxy config files based on discovered upstreams - it does not receive any requests itself. The scalability is handled by HAProxy.