What AWS is calling out
The New Stack, on July 10, published a walk-through of what running Kubernetes across a very large EKS fleet has taught AWS about availability zone failures. The operational take is one line: the failures that hurt production the most are not the ones that trip the alarms, and EKS now has a primitive that treats that mode as its own category.
The piece frames gray failures as a class of their own. A zone is slow but not down. Latency climbs on some paths and stays flat on others. Health checks keep answering. Nothing looks broken enough to justify the on-call pushing the button, so traffic keeps landing there, and the partial outage runs longer than it should.
Per the write-up, EKS zonal shift is the mechanism to redirect traffic away from an impaired zone. AWS now automates that shift on the customer's behalf, so the reordering happens on suspicion rather than on operator confirmation. That is the news underneath the phrase "lessons learned".
How zonal shift moves the traffic
