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docs: add x509 for faq #533

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docs: add x509 for faq #533

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docs: add x509 for faq
QianChenglong May 24, 2020
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Expand Up @@ -72,6 +72,56 @@ Default 60 seconds, can be changed using `metrics-resolution` flag. We are not r

## Known issues

#### Incorrectly configured front-proxy certificate

Metrics Server needs to validate requests coming from kube-apiserver. You can recognize problems with front-proxy certificate configuration if you observe line below in your logs:
```
E0524 01:37:36.055326 1 authentication.go:65] Unable to authenticate the request due to an error: x509: certificate signed by unknown authority
```

To fix this problem you need to provide kube-apiserver proxy-client CA to Metrics Server under `--requestheader-client-ca-file` flag. You can read more about this flag in [Authenticating Proxy](https://kubernetes.io/docs/reference/access-authn-authz/authentication/#authenticating-proxy)


For cluster created by kubeadm:

1. Find your front-proxy certificates by checking arguments passed in kube-apiserver config (by default located in /etc/kubernetes/manifests/kube-apiserver.yaml)

```
- --proxy-client-cert-file=/etc/kubernetes/pki/front-proxy-client.crt
- --proxy-client-key-file=/etc/kubernetes/pki/front-proxy-client.key
```

2. Create configmap including `front-proxy-ca.crt`

```
kubectl -nkube-system create configmap front-proxy-ca --from-file=front-proxy-ca.crt=/etc/kubernetes/pki/front-proxy-ca.crt -o yaml | kubectl -nkube-system replace configmap front-proxy-ca -f -
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```

3. Mount configmap in Metrics Server deployment and add `--requestheader-client-ca-file` flag

```
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@serathius serathius May 25, 2020 •
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(Optional) Have you considered using kubectl patch instead?

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@QianChenglong QianChenglong May 25, 2020 •
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I tried, but it seems that patch cannot modify args.

- args:
- --requestheader-client-ca-file=/ca/front-proxy-ca.crt // ADD THIS!
- --cert-dir=/tmp
- --secure-port=4443
- --kubelet-insecure-tls // ignore validate kubelet x509
- --kubelet-preferred-address-types=InternalIP // using InternalIP to connect kubelet

volumeMounts:
- mountPath: /tmp
name: tmp-dir
- mountPath: /ca // ADD THIS!
name: ca-dir

volumes:
- emptyDir: {}
name: tmp-dir
- configMap: // ADD THIS!
defaultMode: 420
name: front-proxy-ca
name: ca-dir
```

#### Network problems

Metrics server needs to contact all nodes in cluster to collect metrics. Problems with network would can be recognized by following symptoms:
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