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If you have cross zone load balancing disabled and you only have one instance per AZ, how do you ensure that when an instance is down or during a deploy, when not all AZ might have instances, that you don't have downtimes? Cross zone load balancing in NLB seems a must to me if you are constantly deploying new targets.

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There’s a few strategies you can employ. One is to roll each AZ one at a time, and take each out of service first.

Another strategy is to have redundancy in each AZ such that your rolling strategy never takes the AZ itself offline.

Just depends on how much infra you want to manage to be honest. Taking an AZ offline can be as easy as having an ingress hop that signals back to the LBs that it is now failing health checks and should be temporarily removed from service.

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