Platform & DevOps·Placement, resources and the pod lifecycle
all three replicas were on one node and one reboot took the service down, which is exactly what this rule prevents.
Pod anti-affinity
Also calledanti-affinity, spread rule
A rule that keeps copies of the same workload apart — on different nodes, racks or zones — expressed relative to other workloads rather than to node labels. Without it a scheduler optimising for packing will cheerfully place every replica of a service on the same machine, and the redundancy you are paying for is imaginary. Required anti-affinity across zones also caps your replica count at the number of zones, which is a surprise the first time autoscaling hits it.