In the past, I have done Load Balancer status checks against a special /status endpoint. I queried all the connected services (i.e. DB, Redis, etc) with a super fast query (i.e. `SELECT version();`). Monitoring CPU/MEM usage for scaling was separate. Comparing this to checking the home page, what is the best way to setup a health check for your load balancers?
1) If you do have a back-end failure, this setup can cloud the root cause during recovery because your downstream web servers are down as well.
2) Transitory back-end failures can cascade, and your health checks can make this worse as things flap around. You need to be VERY careful with your timers and retry logic, and tune them appropriately. eg, how does `/status` handle a single TCP reset from the DB? When does it decide to timeout if the DB doesn't respond? It's hard to get this right - network errors vs protocol errors vs timeouts are often handled differently at different layers of the controller, and the load balancer has its own retries and timeouts.
3) If this health check is being used for an API, recovery can be more difficult because of thundering herds. eg, 5/5 API servers go down because of a temporary DB failure. Queues and requests backup. 1/5 API servers is restored to service a bit earlier than the others, and immediately goes down again because it's not degrading gracefully under heavy load. Wash/rinse/repeat until you figure out how to load shed.
4) Are you absolutely positive that your app is worthless without a DB/redis/backend-baz, and every endpoint is broken? Ideally, the app will degrade gracefully if certain request can be served from cache, or don't require the failed backend.
5) The failure case where this type of thing might be useful (network partition affecting DB connectivity from a subset of your webservers) isn't very common in the environments I've been involved with.
A far more productive approach if you absolutely need this sort of thing is to implement circuit breakers[1] at the app level, and explicitly make certain tripped breakers a hard failure for the /status endpoint. This has the advantage of not depending solely on synthetic queries, and having very explicit restoration logic.
For load balancer health checks, I prefer ones that hit the controller and expect a 200, and nothing more. (The DB and overall health of the service cluster are monitored through more organic instrumentation.)
I was laughing to myself when I read the Stack Overflow post mortem because I have a healthy pile of healthcheck-too-expensive war stories, and their experience resonated.