So, when using AWS ELB, there's a health check url we use to ping db server / check out bound connection, etc.
If there are unhealthy instances, they are removed. But if the db server is down, our web server is designed to continue function to the best of its ability. (Design for failure).
These 2 concepts seems to conflict each other? If a single server is not health, it'd be removed. If all server is affected, we want to keep them online.
How to solve this dilemma?