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kubeadm: add TS guide note about CoreOS read-only /usr (#19166)

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* kubeadm: add TS guide note about CoreOS read-only /usr

* Update content/en/docs/setup/production-environment/tools/kubeadm/troubleshooting-kubeadm.md

Co-Authored-By: Tim Bannister <tim@scalefactory.com>

Co-authored-by: Tim Bannister <tim@scalefactory.com>
This commit is contained in:
Lubomir I. Ivanov
2020-02-19 02:54:24 +02:00
committed by GitHub
parent 1513a7b29a
commit 2d0bde0458
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@@ -319,4 +319,46 @@ There are at least two workarounds:
```bash
kubectl taint nodes NODE_NAME role.kubernetes.io/master:NoSchedule-
```
## `/usr` is mounted read-only on nodes {#usr-mounted-read-only}
On Linux distributions such as Fedora CoreOS, the directory `/usr` is mounted as a read-only filesystem.
For [flex-volume support](https://github.com/kubernetes/community/blob/ab55d85/contributors/devel/sig-storage/flexvolume.md),
Kubernetes components like the kubelet and kube-controller-manager use the default path of
`/usr/libexec/kubernetes/kubelet-plugins/volume/exec/`, yet the flex-volume directory _must be writeable_
for the feature to work.
To workaround this issue you can configure the flex-volume directory using the kubeadm
[configuration file](https://godoc.org/k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm/v1beta2).
On the primary control-plane Node (created using `kubeadm init`) pass the following
file using `--config`:
```yaml
apiVersion: kubeadm.k8s.io/v1beta2
kind: InitConfiguration
nodeRegistration:
kubeletExtraArgs:
volume-plugin-dir: "/opt/libexec/kubernetes/kubelet-plugins/volume/exec/"
---
apiVersion: kubeadm.k8s.io/v1beta2
kind: ClusterConfiguration
controllerManager:
extraArgs:
flex-volume-plugin-dir: "/opt/libexec/kubernetes/kubelet-plugins/volume/exec/"
```
On joining Nodes:
```yaml
apiVersion: kubeadm.k8s.io/v1beta2
kind: JoinConfiguration
nodeRegistration:
kubeletExtraArgs:
volume-plugin-dir: "/opt/libexec/kubernetes/kubelet-plugins/volume/exec/"
```
Alternatively, you can modify `/etc/fstab` to make the `/usr` mount writeable, but please
be advised that this is modifying a design principle of the Linux distribution.
{{% /capture %}}