* Add necessity of metrics-server for HPA
Current HPA doc1 mentions metrics-server like
For resource metrics, this is the metrics.k8s.io API,
generally provided by metrics-server. It can be launched
as a cluster addon.
The metrics.k8s.io API is mandatory for HPA, so the above means
metrics-server needs to be launched for HPA. However it is difficult
to understand that requirement because the above seems metrics-server
as just a addon, and that is described on small section.
In addition, many people are facing HPA issue that fetching metrics
doesn't work on the internet like
$ kubectl get hpa
NAME REFERENCE TARGETS MINPODS MAXPODS REPLICAS AGE
nginx Deployment/nginx <unknown>/50% 1 3 0 7s
The above sample "<unknown>" shows HPA feature cannot get current
metrics due to metrics-server doesn't work fine.
This adds necessity of metrics-server for HPA directly to solve
the problem.
fixes: #9728
* Copyedit
Ken'ichi Ohmichi
ab3fd0de7e