k8s1.8引入的特性，限制容器存储空间的使用；对于容器资源隔离来说，非常有用，万一应用程序失控，写大量日志把node空间写满，影响就大了。

使用很简单，和cpu\memcache一样，如：

resources:
  requests:
    cpu: 1
    memory: 2048Mi
    ephemeral-storage: 2Gi
  limits:
    cpu: 2
    memory: 2048Mi
    ephemeral-storage: 5Gi

但，这玩意生效有条件：

猛一看，ephemeral-storage只能对镜像存放在“根分区”下的容器有效，也就是默认的"Docker Root Dir: /var/lib/docker"必须在根分区下；对于一个正常点的运维来说，程序路径与根分区分离是基本的做法，对于一个有节操的k8s运维来说，将/var/lib/docker用独立分区，再正常不过了。

测试结果如下：

docker Version: 18.09.8
k8s version:1.13.8
Docker Root Dir: /var/lib/docker
kubelet的--root-dir: 默认（/var/lib/kubelet）

/var/lib/docker在根分区下，ephemeral-storage有效果
/var/lib/docker不在根分区下（作为单独分区），ephemeral-storage没有效果

这有点沮丧，这么有用的功能难道不能派上用场，不太相信，求助github，有线索：https://github.com/kubernetes/enhancements/issues/361

其中有这样的回复：

The behavior you describe should work regardless of this feature. Make sure you have --root-dir set correctly. Docker reports its root directory to the kubelet, so as long as your images are stored on the same partition that contains /var/lib/docker (or whatever your docker root dir is), this should work correctly.

这句话貌似有误，/var/lib/docker应该写错了，换成/var/lib/kubelet才好理解，因为/var/lib/kubelet是--root-dir的默认配置，总的来说，意思是只要“Docker Root Dir: /var/lib/docker”和“kubelet --root-dir”在一个分区，就能起作用。

测试结果就是如此。

/var/lib/docker是独立分区的情况下，怎样实现kubelet的root-dir与/var/lib/docker一个分区呢？两个选择：

方案1. 修改root-dir

kubectl drain nodename
systemctl stop docker
systemctl stop kubelet

修改/usr/lib/systemd/system/kubelet.service.d/10-kubeadm.conf：
增加--root-dir=/var/lib/docker/kubelet/
将/var/lib/kubelet/修改为/var/lib/docker/kubelet/

修改/etc/kubernetes/kubelet.conf
将/var/lib/kubelet/修改为/var/lib/docker/kubelet/

mv /var/lib/kubelet /var/lib/docker

systemctl daemon-reload
systemctl start docker
systemctl start kubelet

有个遗留问题，重启kubelet后，又自动生产了以下目录，但kubelet运行正常

# tree /var/lib/kubelet -L 3   
/var/lib/kubelet
└── device-plugins
    ├── DEPRECATION
    ├── kubelet_internal_checkpoint
    └── kubelet.sock

 

方案2.root-dir软链到/var/lib/docker下

kubectl drain nodename
systemctl stop docker
systemctl stop kubelet

mv /var/lib/kubelet /var/lib/docker
ln -s /var/lib/kubelet /var/lib/docker/kubelet

systemctl start docker
systemctl start kubelet
systemctl uncordon nodename

PS：上述mv操作前，先df确认下是否有/var/lib/kubelet下的文件被mount，有则先umount再mv，否则报错“Device or resource busy”

# mv kubelet/ /var/lib/docker
mv: cannot remove ‘kubelet/pods/73a3d42a-b2a5-11e9-8e8d-005056b4f9d3/volumes/kubernetes.io~secret/kube-proxy-token-jccg4’: Device or resource busy
mv: cannot remove ‘kubelet/pods/73a36f7a-b2a5-11e9-8e8d-005056b4f9d3/volumes/kubernetes.io~secret/etcd-certs’: Device or resource busy
mv: cannot remove ‘kubelet/pods/73a36f7a-b2a5-11e9-8e8d-005056b4f9d3/volumes/kubernetes.io~secret/calico-node-token-tzfv8’: Device or resource busy
mv: cannot remove ‘kubelet/pods/e2542d86-ceef-11e9-8e8d-005056b4f9d3/volumes/kubernetes.io~secret/node-exporter-token-5926x’: Device or resource busy

# df -h
tmpfs                        20517564       0  20517564   0% /var/lib/kubelet/pods/73a3d42a-b2a5-11e9-8e8d-005056b4f9d3/volumes/kubernetes.io~secret/kube-proxy-token-jccg4
tmpfs                        20517564       0  20517564   0% /var/lib/kubelet/pods/73a36f7a-b2a5-11e9-8e8d-005056b4f9d3/volumes/kubernetes.io~secret/etcd-certs
tmpfs                        20517564       0  20517564   0% /var/lib/kubelet/pods/73a36f7a-b2a5-11e9-8e8d-005056b4f9d3/volumes/kubernetes.io~secret/calico-node-token-tzfv8
tmpfs                        20517564       0  20517564   0% /var/lib/kubelet/pods/e2542d86-ceef-11e9-8e8d-005056b4f9d3/volumes/kubernetes.io~secret/node-exporter-token-5926

测试结果：

在容器中dd生成一个5G的文件，终于可以evicted了。

# kubectl get pods -o wide                          
NAME                           READY   STATUS    RESTARTS   AGE     IP              NODE                   NOMINATED NODE   READINESS GATES
ptest-trade-747b894f54-mhrv4   0/1     Evicted   0          3m37s   <none>          lin-40-16-206.lb.com   <none>           <none>
ptest-trade-747b894f54-tx847   0/1     Running   0          26s     10.46.206.96    lin-40-16-206.lb.com   <none>           <none>


# kubectl describe pod p7881-trade-747b894f54-mhrv4 
Events:
  Warning  Evicted              12s  kubelet, lin-40-16-206.lb.com  Pod ephemeral local storage usage exceeds the total limit of containers 5Gi.
  Warning  ExceededGracePeriod  2s   kubelet, lin-40-16-206.lb.com  Container runtime did not kill the pod within specified grace period.
  Normal   Killing              1s   kubelet, lin-40-16-206.lb.com  Killing container with id docker://ptest-trade:Need to kill Pod