AWS Elastic Load Balancer Black Hole
Problem -
Load balancer acts as a proxy between client and server ensuring requests from multiple clients get fairly distributed to cluster of servers.
Whenever a server deregisters from ELB, ELB continues to forward it the requests to a black hole i.e. a place which no longer exists.
Clients many a times don't realize that their requests are getting lost if these requests are more of one way traffic without any response expectation.
Solution -
Once in a while, clients should send a request expecting a response esp. over a long lived connection. That way, if the actual server is down, client will know.
Instead of deregistering a server, shutting it down is better because that way, the server connections to the ELB are closed and the upstream clients are notified appropriately that what they were talking to is no longer available.
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