Earlier this year, AWS had a major Availability Zone outage in us-east-1. Only one AZ went down, but if your workloads were running there, you know how it went: alerts firing, runbooks open, manual fixes, and a race to move traffic before customers noticed. For those who were not lucky enough to be in a different AZ, it raised an obvious question: why isn’t there a button for this? There is. It’s called ARC Zonal Shift. ...
Introduction Topology Aware Routing (TAR) is a Kubernetes feature designed to keep traffic within the same availability zone (AZ). This can reduce cross-AZ traffic costs on cloud providers like AWS and GCP, where inter-AZ traffic incurs charges. Additionally, it can lower latency by keeping network requests local. However, TAR is not a silver bullet. While it helps optimize costs and performance, it strictly prohibits cross-zone traffic, regardless of the system’s health or workload distribution. This limitation can lead to unintended service disruptions. ...