I disagree. If application is not deployed correctly that server is definitely not healhy. If you mark it healthy, users will see some page not found error (If checker accepts codes 100-500, then it would also accept 404 - page not found.)- which is even worse than if you don't have session replication (in that case they will think they were just logged out, and not that a server went down). Users should never encouter HTTP code 500 or 404 if URL was correct. I do not think such a check this load balancer is performing is OK. The acceptable HTTP response code should be configurable. Unfortunately the link you posted doesn't mention how to change acceptable HTTP response code.
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