pod readiness gate

https://kubernetes-sigs.github.io/aws-alb-ingress-controller/guide/ingress/pod-conditions/

The condition status on a pod will only be set to True when the corresponding target in the ALB target group shows a health state of »Healthy«. This prevents the rolling update of a deployment from terminating old pods until the newly created pods are »Healthy« in the ALB target group and ready to take traffic.

只有ALB ingress设置了readiness gate对应的status之后，pod才真正是ready，deployment才能继续滚动更新。

ALB设置pod readiness gate的前提条件是，pod 的container已经ready（通过readiness check）