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0 pointsTenzer10y ago0 comments

Regarding how the ELB works, then I think the AWS engineers have a different idea on how to implement stuff. AWS is very much a dynamic platform and the engineers seem to have embraced this when they came up with this solution.

It doesn't necessarily mean you can't use websockets through an ELB, it just means that you would need to be able to handle reconnects, but that shouldn't be a new challenge for any system relying on connections being open for long. Also, the load balancer servers doesn't switch every 60 seconds, you can have connections running for a lot longer than that. I would also assume the load balancers keep handling connections for a while after they were taken out of the DNS rotation, in order to make sure DNS caches are updated before the IP addresses stops working.

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6 comments · 3 top-level

lisper10y ago· 2 in thread

> you would need to be able to handle reconnects, but that shouldn't be a new challenge for any system relying on connections being open for long

That's true, but it kind of misses the point. Normally, if a connection is dropped it means something has gone wrong. In this case, connections are dropped by design, and there is no way (AFAICT) to work around this. Designing so that behavior that is otherwise the result of things going wrong is now the normal designed-for behavior is, IMHO, the very definition of Bad Design.

ishigoemon10y ago

I'd argue that this design promotes building reliable applications. A system that cannot reconnect is fragile, and the best way to know if the system can handle that failure is to occasionally induce the event. Assuming that you are running across a lossless, ideal network is, IMHO, the very definition of Bad Design.

"If it hurts, do it more often." -- Martin Fowler

lisper10y ago

Certainly systems should be designed to be robust against failures. But encouraging this by deliberately producing failures in production seems like a bad idea to me. It's kind of like saying, "Let's see if the new hull design works by deliberately steering the boat into an iceberg!"

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JimmyL10y ago· 1 in thread

AWS support has said that ELBs will continue to accept connections (and use the correct backend) for at least an hour after the CNAME stops resolving to a particular IP.

lisper10y ago

Ah, I didn't know that. That makes a big difference.

But there's still a significant hole here: is there any way to get notified that this has happened other than polling the DNS?

bmurphy197610y ago

My analysis shows an AWS ELB changes ip addresses on us roughly every 2 weeks. Often enough to cause problems if you aren't prepared but infrequent enough to give you a false confidence that things are working as designed.

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