Merge pull request #60979 from kawych/master

Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Add Troubleshooting sections to Heapster and Metrics Server addons documentation

**What this PR does / why we need it**:
Add Troubleshooting sections to Heapster and Metrics Server addons documentation

**Release note**:
```release-note
NONE
```

cluster/addons/cluster-monitoring/README.md

@@ -5,4 +5,17 @@ Heapster collects signals from kubelets and the api server, processes them, and
 
 More details can be found in [Monitoring user guide](http://kubernetes.io/docs/user-guide/monitoring/).
 
+## Troubleshooting
+
+Heapster supports up to 30 pods per cluster node. In clusters where there are more running pods, Heapster may be throttled or fail with OOM error. Starting with Kubernetes 1.9.2, Heapster resource requirements may be overwritten manually. [Learn more about Addon Resizer configuration](https://github.com/kubernetes/autoscaler/tree/master/addon-resizer#addon-resizer-configuration)
+
+### Important notices
+
+Decreasing resource requirements for cluster addons may cause system instability. The effects may include (but are not limited to):
+  - Metrics not being exported
+  - Horizontal Pod Autoscaler not working
+  - `kubectl top` not working
+
+Overwritten configuration persists through cluster updates, therefore may cause all effects above after a cluster update.
+
 [![Analytics](https://kubernetes-site.appspot.com/UA-36037335-10/GitHub/cluster/addons/cluster-monitoring/README.md?pixel)]()

cluster/addons/metrics-server/README.md

@@ -0,0 +1,20 @@
+# Metrics Server
+
+[Metrics Server](https://github.com/kubernetes-incubator/metrics-server) exposes
+core Kubernetes metrics via metrics API.
+
+More details can be found in [Core metrics pipeline documentation](https://kubernetes.io/docs/tasks/debug-application-cluster/core-metrics-pipeline/).
+
+## Troubleshooting
+
+Metrics Server supports up to 30 pods per cluster node. In clusters where there are more running pods, Metrics Server may be throttled or fail with OOM error. Starting with Kubernetes 1.9.2, Metrics Server resource requirements may be overwritten manually. [Learn more about Addon Resizer configuration](https://github.com/kubernetes/autoscaler/tree/master/addon-resizer#addon-resizer-configuration)
+
+### Important notices
+
+Decreasing resource requirements for cluster addons may cause system instability. The effects may include (but are not limited to):
+  - Horizontal Pod Autoscaler not working
+  - `kubectl top` not working (starting with Kubernetes 1.10)
+
+Overwritten configuration persists through cluster updates, therefore may cause all effects above after a cluster update.
+
+[![Analytics](https://kubernetes-site.appspot.com/UA-36037335-10/GitHub/cluster/addons/cluster-monitoring/README.md?pixel)]()