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This is why their new load balancer variants are insidious, as they require you to have instances in multiple availability zones :/.

But you don't need to enable cross-AZ traffic. Or to be precise you can disable it (if you give up on some features like stickiness).

Only helps if your instances don’t need to talk to each other

Instances can still do cross-AZ traffic, this just prevents the incoming load balanced traffic from crossing AZs.

They did this with managed Kafka too.