kubernetes continually evict pod when node's inode exhausted
kubernetes等容器技术可以将所有的业务进程运行在公共的资源池中，提高资源利用率，节约成本，但是为避免不同进程之间相互干扰，对底层docker, kubernetes的隔离性就有了更高的要求，kubernetes作为一门新盛的技术，在这方面还不够成熟， 近期在一个staging集群就发生了，inode资源被耗尽的事件：
现象
在测试集群中，许多pod被Evicted掉
[root@node01 ~]$ kubectl get pods
NAME READY STATUS RESTARTS AGE
default-http-backend-78d96f979f-5ljx4 1/1 Running 0 8d
perfcounter-proxy-8b884c4ff-2ng4j 0/2 Evicted 0 1d
perfcounter-proxy-8b884c4ff-5hq5k 0/2 Evicted 0 1d
perfcounter-proxy-8b884c4ff-66qfw 0/2 Evicted 0 23h
perfcounter-proxy-8b884c4ff-6hf7f 0/2 Evicted 0 23h
perfcounter-proxy-8b884c4ff-6knrm 0/2 Evicted 0 1d
perfcounter-proxy-8b884c4ff-6m9p5 0/2 Evicted 0 1d
perfcounter-proxy-8b884c4ff-768g6 0/2 Evicted 0 1d
perfcounter-proxy-8b884c4ff-7d74k 0/2 Evicted 0 20h
perfcounter-proxy-8b884c4ff-998kx 0/2 Evicted 0 1d
perfcounter-proxy-8b884c4ff-bmvjc 0/2 Evicted 0 1d
perfcounter-proxy-8b884c4ff-cbh6m 0/2 Evicted 0 23h
perfcounter-proxy-8b884c4ff-cd8jb 0/2 Evicted 0 1d
perfcounter-proxy-8b884c4ff-d2m25 0/2 Evicted 0 1d
perfcounter-proxy-8b884c4ff-dgtkk 0/2 Evicted 0 1d
perfcounter-proxy-8b884c4ff-ftf2r 0/2 Evicted 0 20h
perfcounter-proxy-8b884c4ff-hdz9x 0/2 Evicted 0 23h
perfcounter-proxy-8b884c4ff-hgftx 0/2 Evicted 0 23h
perfcounter-proxy-8b884c4ff-ks5sq 0/2 Evicted 0 1d
perfcounter-proxy-8b884c4ff-kwf6x 0/2 Evicted 0 23h
perfcounter-proxy-8b884c4ff-lnqct 2/2 Running 0 20h
perfcounter-proxy-8b884c4ff-ngs9s 0/2 Evicted 0 2d
pod驱逐一般发生在某个node状态notready后，比如说磁盘写满，网络异常等，此时kuernetes就会将该异常node上面的pod进行驱逐，以免影响服务实例数，但是上面显示的如此频繁的驱逐是一定有问题的，机器状态不稳定，不断的flapping，执行kubectl describe node node04之后发现是由于node04机器上inode资源不足导致：
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Warning EvictionThresholdMet 3d (x3 over 4d) kubelet, node04.kscn Attempting to reclaim nodefsInodes
Normal NodeHasDiskPressure 3d (x3 over 4d) kubelet, node04.kscn Node node04.kscn status is now: NodeHasDiskPressure
Normal NodeHasNoDiskPressure 3d (x3 over 4d) kubelet, node04.kscn Node node04.kscn status is now: NodeHasNoDiskPressure
Warning EvictionThresholdMet 2d (x8 over 2d) kubelet, node04.kscn Attempting to reclaim nodefsInodes
Normal NodeHasDiskPressure 2d (x2 over 2d) kubelet, node04.kscn Node node04.kscn status is now: NodeHasDiskPressure
Normal NodeHasNoDiskPressure 2d (x2 over 2d) kubelet, node04.kscn Node node04.kscn status is now: NodeHasNoDiskPressure
Warning EvictionThresholdMet 20h (x9 over 1d) kubelet, node04.kscn Attempting to reclaim nodefsInodes
Normal NodeHasDiskPressure 20h (x6 over 1d) kubelet, node04.kscn Node node04.kscn status is now: NodeHasDiskPressure
Normal NodeHasNoDiskPressure 20h (x6 over 1d) kubelet, node04.kscn Node node04.kscn status is now: NodeHasNoDiskPressure
登录到node04，查看后确实/home分区inode数据可用比较少
[root@node04 gaorong]# df -i
Filesystem Inodes IUsed IFree IUse% Mounted on
/dev/vda1 1310720 150802 1159918 12% /
devtmpfs 4116012 359 4115653 1% /dev
tmpfs 4118414 61 4118353 1% /dev/shm
tmpfs 4118414 2083 4116331 1% /run
tmpfs 4118414 15 4118399 1% /sys/fs/cgroup
/dev/vdb 819200 762459 56741 94% /home
解决
首先需要确定到底是那个服务导致inode耗尽的，确定inode占用较多的是那个目录， 根据目录可以确定是那个服务了，这里使用inodes这个工具来显示每个目录的占用inodes数目，发现/home/docker/aufs这个目录占用较多:
[root@node04 gaorong]# inodes --d /home/docker/aufs/ -t 50000 -e 500
------------------------------------------
[CONFIG] Directory to scan specified as /home/docker/aufs/
------------------------------------------
[CONFIG] Tree directories above 50000 inodes
------------------------------------------
[CONFIG] Exclude directories below 100 inodes
------------------------------------------
INODE USAGE SUMMARY
------------------------------------------
INODES | SIZE | DIRECTORY
------------------------------------------
493221 | 16G | diff
--5417 | --130M | --016fe5bdd62c9264bcda0c44ef1548aaf8b82acfee2b0b8943e7394218118550
--166 | --65M | --047d364456b37521445751910a4251faa6adcd50908f4d2f064ecbe80f20d332
--10536 | --203M | --0a0b37e475c91a49cea4d732f83e6f87010edae86e25f4c7e14203e66c4122ea
... 此处省略若干行....
--2050 | --64M | --f5fa7a7efabad90d1dfa4519f5c7fae611bdbfc9a9b43eb58b8c8bc035a15336
--8714 | --304M | --f7618789addc900474c931ce9bbdc52abd5bf61ab98cd23d46e6189bd41094d1
--241 | --174M | --faf7ea4dc438088688dded3164ce7a11018a7a5dc346d621b43965bc3b0e60cb
--10921 | --325M | --fb08d1ed58bcdd3374ed835fcb27554ab52bcdd4822d502eb00066dec4d70650
386 | 1.6M | layers
179712 | 6.4G | mnt
--7110 | --467M | --06feaf7d4336e97f3b11440865b97c0fadedd5488126215216be616c656e82f5
--10764 | --337M | --26f394cad00c1876f832e2a4fb83816253dd8d70303a0d3b96a46edaf3564a05
--18914 | --1.2G | --3912a58cf254540753d8accf69ed7a8c1c9d9539d73d35be9bd105dde94effe5
--2965 | --168M | --401c0221bb62e36b3fcfb181420b64ec21147783860c72732299dba2f69f0280
--3759 | --85M | --773333aef4b7f00f1f585b4c41fcbe20906c28b53999cfb78df268034d9b59e4
--18692 | --626M | --79a76870faa7ed5f218b87e942d12523e5a9dd14cdb8449ccea5af279f45b526
--26462 | --758M | --81d5c11dcc68df6ceee547fe84236c0234e4a63844e4ffc19047b6846185871b
--2333 | --24M | --91bc77e078602f1e7285d2d742368a7a17ad0c0c3c736305fcbe68a11aa23e4c
--10623 | --218M | --97a5ff749684b366c4a3ecff5536990e1db907577065deb7839e9da3c116ff93
--18914 | --1.2G | --a4b945841c02a8a38463096f5cc1fd314563d94c78f8ccc92221b7f2571b2c3c
--6749 | --157M | --aaa03c1ad6cd6fb332cce4c033eb74e2ae9f62364d5ea6e9d434aa88b6925644
--17989 | --488M | --b6fb0a75102f0f25aa14a2f76b3013fab19c3f49b9ab49a2a8c230d52b84ff74
--28536 | --674M | --d01bdbddb09cf36411c6179cb9657390eb4ed0f440f8aa05c94e38f7de49439c
--5284 | --113M | --e3c555a3df172a2cd852cff210b43693bbc1cfa0b7cb5dbaee7645a4abdcfdb0
------------------------------------------
673320 | 22G | /home/docker/aufs/
------------------------------------------
/home/docker/aufs目录是docker采用aufs作为storage driver时用来存储镜像layer的目录，镜像中的每个文件都会在这里找到对应的文件。(docker默认的存储位置是/var/lib/docker，此环境因为项目需要改为/home/docker目录)，aufs中小文件太多导致inode耗尽也是是比较常见的问题，如果使用deviceMapper等这种块设备的storage driver就不存在这个问题了。kubernetes会定期自动清理imagefs中的文件，删除没用的镜像和容器， 如果还是没有足够的资源的话才会驱逐pod。经过确认之后，该node上面的镜像都在使用中， kubernetes应该是尽力去清理镜像了， 清理完之后还是有inode pressure， 于是只能驱逐pod了， 驱逐之后node状态变为ready , 随后有新创建的pod会调度到该node上面，运行一段时间后inode资源又不足， 又进行驱逐回收... 如此循环往复，导致集群状态不稳定，有大量的pod被evict掉。因为Image资源我们没有办法继续清理，只能交给kubernetes去回收了。看看还有那些目录占用资源较多。
上面显示aufs占用的是673320，但df -i显示占用的inode数目是819200，说明还有其他地方导致占用比较多，约20w。仔细查找后发现另一个占用比较多的目录home/docker/volumes。
[root@node04 docker]# inodes --d /home/docker/volumes -t 50000 -e 500
------------------------------------------
[CONFIG] Directory to scan specified as /home/docker/volumes
------------------------------------------
[CONFIG] Tree directories above 50000 inodes
------------------------------------------
[CONFIG] Exclude directories below 500 inodes
------------------------------------------
INODE USAGE SUMMARY
------------------------------------------
INODES | SIZE | DIRECTORY
------------------------------------------
10995 | 715M | 0afe5e70b2b22d1bee735977a8e931e2f2a65da5d79c08babf08a4de1a69877a
6576 | 378M | 0d0453ed64d4e830f408cf920a5ae13cefe1d4bfe3444464b9e612e699872a17
8497 | 414M | 1708cd1ce59818132e93bada3db8926a9eb03e08f553ad66f9df738424408704
6862 | 289M | 2940dea37d29501423d6eb50056034c89a9caf92cd2cd567ea3ffc02b54c813d
3224 | 102M | 2fe657a647b3c8b9b9a4d552cdeee682bd465edff14d90477a3277d79eeed807
9522 | 409M | 354c182b47707cc173de72ccf7ad99cabccc61d1f44e70a72d66a32334894d14
15204 | 533M | 4d49d25d55ab02f59fef56d984bfd811c3a2c8ec02378c0d7e860fac9df9d3ee
9546 | 407M | 4e1d2bb4ab8ca730df17b8a16910740dba8046cf8d9dc71625a017d67e16f95f
9205 | 408M | 51acc932cc72f620c9fded3cb93ea877467b78364731d35e58c08a72b2b247c2
9801 | 481M | 56a0e0a016c8c65cc27430dcd4053a18dec81bfd444da505148fe3fc30f4506c
17675 | 473M | 6ee2b44c4351790ef36bb7a1774fa2647b6d4c9ecc5dce1bcb33a9a522ea0808
9035 | 484M | 7928e4c94867ee49de041565e92a4c36517a6a7f904149dbd5b7df331b4f6a0e
7788 | 285M | 85c76690344f6b11ccaa95153df0b317b6ade6a6f6179e19ad3c40b9c2ba4d27
11193 | 856M | 8d51785afbeb6754e70286c73ee1fa5044b8eab02b606d692e64eea342303449
3054 | 79M | 9252da456a675c2c6519568b1bae3c7e410f1d5dc89e47f4e13bdd26964367e4
8604 | 377M | 962d4c2e6dd47f642aafe49557b660b9767b859c472ae0002c4f2ef4789bb350
5366 | 132M | 9bb9e9d8eff02f63eeea8dee9c351d6608b3e061d659a013ee5370b961961707
9171 | 480M | b8edb07ae19b7e5920b3aa254fb437670cc2f21f570cde693a778400a8e2784f
15088 | 592M | bd017c95ed823d8bbe7e4d7ee8bb40160c86b613fe9683c9a09a1e4dde3f017e
7813 | 285M | bf89566ba7852b07dc52fa5ef9d3a467dbcc5608532f6c2b0682feebed508401
14454 | 1.2G | c5a858a1ea25032f90d97b3765bebd32ffcecd5b911087451cd6d4fdaee1c92c
10427 | 467M | c9548dfca3e3de3dd1387c47a1a6771fe8aaf3908ab17a58287dad8511fa416c
4530 | 215M | cc4bde58318575c1c5fa8dde53e05d1f082b5a9944cecec23ac50989cebd963c
8036 | 381M | ced3dd5ecabdde6e313db4514290b30f735f8f18431ac6cb848d65d980e101b5
6439 | 374M | d0b3ca6b65cf9a686f0d521a813cb27d91e9dfd6078b80171e1dc16fdba6a922
15891 | 589M | e6292e24cc7d4a5ec43ed5ede58e9356b369e8e72f24327d297dd668fc20a640
11088 | 831M | ef175210467e4b58fb2215e35d679435699f8ce1f043a6225ff4fa1033c0e345
------------------------------------------
259083 | 15G | /home/docker/volumes
------------------------------------------
/home/docker/volumes目录是docker创建的，用于支持VOLUME 定义匿名卷，(默认路径是 /var/lib/docker/volumes ， 此处是由于项目需要改变为 /home/docker/volumes目录)。我们平时启动容器的时候，挂载数据卷一般是执行docker run -ti -v /home/gaorong/:/home/gaorong nginx，这样就将容器里的"/home/gaorong"目录和宿主机上的"/home/gaorong"绑定在一起， 但是如果我们没有显式指定要挂载在宿主机的那个目录， 那docker 只能为其创建一个默认的目录了，比如执行docker run -ti -v /home/gaorong nginx， 他在容器中的目录"/home/gaorong"，其实挂载的是宿主机上/var/libe/docker/volumes这个目录。
我们看看里面有些什么？
[root@node04 volumes]# tree -L 3
.
├── 0ad528934774355e22f4afa2df56a85cbe18bed0f922f37d054c1c0362baf648
│ └── _data
│ └── luhualin
├── 16d08b2bdb76ebeede9b6ee6da1378e44cf47ba825d6545f1a0ead8e21f9ffc0
│ └── _data
├── 1708cd1ce59818132e93bada3db8926a9eb03e08f553ad66f9df738424408704
│ └── _data
│ ├── global-bigdata-micsql
│ └── global-bigdata-micsql.tmp
├── 1a5c420084d42c370ac670d6e483cc2a960f4da71cf0fa0a765e1bf099a7c027
│ └── _data
│ ├── data
│ ├── meta
│ └── wal
├── 1fca6975f0af913c116aad7273a32f0a2795e62f3439ab779b39524c9434cf5d
│ └── _data
│ └── ContainerCloud
├── 3bb2d14dd39cca6d93296c742bbce8446c79a5c441b81c60d07a661a9a252b63
│ └── _data
├── 3c4845e864469457b3dac0a077e7f542db0dcfd9e20fbb112fde0e514d23a261
│ └── _data
├── 53ea91b9a833cb676d71cf336ffab97f20fe326bbd165427b64c9685e26a0f1f
│ └── _data
│ └── ContainerCloud
...此处省略若干行...
├── fc82dfd844191eb8baf1a68d3378e8fe0553d9cc705eb2fdfd3e5398a17783e2
│ └── _data
│ ├── k8s-node-frigga
│ └── k8s-node-frigga.tmp
├── fd3dec13f142dc59ad8dbbc2acf3841fd893f6d548ebe74aa2348af8f26fa448
│ └── _data
└── metadata.db
可以看到其中有许多小文件，该集群中有些CICD 任务， 下载了许多源码文件，小而多的文件占用inode较多。 我们可以通过docker volume ls查看到目前没有被删除的匿名volume
[root@node04 volumes]# docker volume ls
DRIVER VOLUME NAME
local 3a42fa60c84ebf1363c9b65c874a86e5663c883f2629edd0ac22575893f9a9ae
local 2714f98661dfb0c6f94c99a0acf2c33f30d491667ce251e6499b069497095260
...此处省略若干行...
local ac04c0925a0203cd87c55eaf1c6f094cf7e0b2cf3173c80d9de459f2aca1ccd4
接下来就需要定位是那个容器/pod创建的，为什么会创建匿名volume。 执行docker ps -a | grep -v NAME | awk '{print $1}' | xargs docker inspect | grep -B 100 3a42fa60c84ebf1363c9b65c874a86e5663c883f2629edd0ac22575893f9a9ae看一看是哪个容器创建的这些volume，找到其中一个容器 docker inpsect一下：
[root@node04 global-bigdata]# docker inspect 25b3d4902305
[
{
"Id": "25b3d4902305258371fbc71851dcb4aade62e393f567750f4776b7a3843e1ae4",
"Created": "2019-02-27T06:58:27.091296766Z",
"Path": "/docker-entrypoint.sh",
"Args": [
"zkServer.sh",
"start-foreground"
],
...此处省略若干行...
"GraphDriver": {
"Data": null,
"Name": "aufs"
},
"Mounts": [
{
"Type": "bind",
"Source": "/home/kubelet/pods/1461d38d-3a5d-11e9-a499-fa163e08f614/volumes/kubernetes.io~secret/default-token-h7vj9",
"Destination": "/var/run/secrets/kubernetes.io/serviceaccount",
"Mode": "ro,rslave",
"RW": false,
"Propagation": "rslave"
},
{
"Type": "bind",
"Source": "/home/kubelet/pods/1461d38d-3a5d-11e9-a499-fa163e08f614/etc-hosts",
"Destination": "/etc/hosts",
"Mode": "",
"RW": true,
"Propagation": "rprivate"
},
{
"Type": "bind",
"Source": "/home/kubelet/pods/1461d38d-3a5d-11e9-a499-fa163e08f614/containers/zk/1d590aa4",
"Destination": "/dev/termination-log",
"Mode": "",
"RW": true,
"Propagation": "rprivate"
},
{
"Type": "volume",
"Name": "ac04c0925a0203cd87c55eaf1c6f094cf7e0b2cf3173c80d9de459f2aca1ccd4",
"Source": "/home/docker/volumes/ac04c0925a0203cd87c55eaf1c6f094cf7e0b2cf3173c80d9de459f2aca1ccd4/_data",
"Destination": "/data",
"Driver": "local",
"Mode": "",
"RW": true,
"Propagation": ""
},
{
"Type": "volume",
"Name": "3a42fa60c84ebf1363c9b65c874a86e5663c883f2629edd0ac22575893f9a9ae",
"Source": "/home/docker/volumes/3a42fa60c84ebf1363c9b65c874a86e5663c883f2629edd0ac22575893f9a9ae/_data", <- 注意看这里
"Destination": "/datalog",
"Driver": "local",
"Mode": "",
"RW": true,
"Propagation": ""
},
{
"Type": "volume",
"Name": "2714f98661dfb0c6f94c99a0acf2c33f30d491667ce251e6499b069497095260",
"Source": "/home/docker/volumes/2714f98661dfb0c6f94c99a0acf2c33f30d491667ce251e6499b069497095260/_data",
"Destination": "/logs",
"Driver": "local",
"Mode": "",
"RW": true,
"Propagation": ""
}
],
"Config": {
"Hostname": "zk-7848b46c9d-6nqhz",
"Domainname": "",
"User": "0",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"ExposedPorts": {
"2181/tcp": {},
"2888/tcp": {},
"3888/tcp": {}
},
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Cmd": [
"zkServer.sh",
"start-foreground"
],
"Healthcheck": {
"Test": [
"NONE"
]
},
"ArgsEscaped": true,
"Volumes": {
"/data": {},
"/datalog": {},
"/logs": {}
},
"WorkingDir": "/zookeeper-3.4.13",
"Entrypoint": [
"/docker-entrypoint.sh"
],
"OnBuild": null,
"Labels": {
"annotation.io.kubernetes.container.hash": "ee6d75c4",
"annotation.io.kubernetes.container.ports": "[{\"containerPort\":2181,\"protocol\":\"TCP\"}]",
"annotation.io.kubernetes.container.restartCount": "0",
"annotation.io.kubernetes.container.terminationMessagePath": "/dev/termination-log",
"annotation.io.kubernetes.container.terminationMessagePolicy": "File",
"annotation.io.kubernetes.pod.terminationGracePeriod": "30",
"io.kubernetes.container.logpath": "/var/log/pods/1461d38d-3a5d-11e9-a499-fa163e08f614/zk/0.log",
"io.kubernetes.container.name": "zk",
"io.kubernetes.docker.type": "container",
"io.kubernetes.pod.name": "zk-7848b46c9d-6nqhz",
"io.kubernetes.pod.namespace": "rpc",
"io.kubernetes.pod.uid": "1461d38d-3a5d-11e9-a499-fa163e08f614",
"io.kubernetes.sandbox.id": "a0fd95b0bb06a573e385f23dc21187c23b8232d59a252d0d8790770e946851a5"
}
},
}
]
看到确实就是该容器mount这个目录， 其对应的image是zookper这个image, 我们看看其DockerFile是怎么写的：
[root@node04 global-bigdata]# docker image history zookper
IMAGE CREATED CREATED BY SIZE COMMENT
06b178591ab3 3 weeks ago /bin/sh -c #(nop) CMD ["zkServer.sh" "start… 0B
<missing> 3 weeks ago /bin/sh -c #(nop) ENTRYPOINT ["/docker-entr… 0B
<missing> 3 weeks ago /bin/sh -c #(nop) COPY file:e241c4b758b1c071… 1.13kB
<missing> 3 weeks ago /bin/sh -c #(nop) ENV PATH=/usr/local/sbin:… 0B
<missing> 3 weeks ago /bin/sh -c #(nop) EXPOSE 2181 2888 3888 0B
<missing> 3 weeks ago /bin/sh -c #(nop) VOLUME [/data /datalog /l… 0B <- 注意看这里
<missing> 3 weeks ago /bin/sh -c #(nop) WORKDIR /zookeeper-3.4.13 0B
<missing> 3 weeks ago |2 DISTRO_NAME=zookeeper-3.4.13 GPG_KEY=C61B… 61.1MB
<missing> 3 weeks ago /bin/sh -c #(nop) ARG DISTRO_NAME=zookeeper… 0B
<missing> 3 weeks ago /bin/sh -c #(nop) ARG GPG_KEY=C61B346552DC5… 0B
<missing> 3 weeks ago /bin/sh -c set -ex; adduser -D "$ZOO_USE… 4.83kB
<missing> 3 weeks ago /bin/sh -c #(nop) ENV ZOO_USER=zookeeper ZO… 0B
<missing> 3 weeks ago /bin/sh -c apk add --no-cache bash s… 4.12MB
<missing> 3 weeks ago /bin/sh -c set -x && apk add --no-cache o… 79.5MB
<missing> 3 weeks ago /bin/sh -c #(nop) ENV JAVA_ALPINE_VERSION=8… 0B
<missing> 3 weeks ago /bin/sh -c #(nop) ENV JAVA_VERSION=8u191 0B
<missing> 3 weeks ago /bin/sh -c #(nop) ENV PATH=/usr/local/sbin:… 0B
<missing> 3 weeks ago /bin/sh -c #(nop) ENV JAVA_HOME=/usr/lib/jv… 0B
<missing> 3 weeks ago /bin/sh -c { echo '#!/bin/sh'; echo 'set… 87B
<missing> 3 weeks ago /bin/sh -c #(nop) ENV LANG=C.UTF-8 0B
<missing> 4 weeks ago /bin/sh -c #(nop) CMD ["/bin/sh"] 0B
<missing> 4 weeks ago /bin/sh -c #(nop) ADD file:2a1fc9351afe35698… 5.53MB
原来是DockerFile中指定了VOLUME，但在启动改pod/容器的时候却没有mount到具体的某个目录，所以就会docker会创建一个匿名volume， 挂载到/home/docker/volume下，在其中写入大量小文件，进而占用该文件系统的inode。
查看官方的Dockfile文档里有这么一句话：
The host directory is declared at container run-time: The host directory (the mountpoint) is, by its nature, host-dependent. This is to preserve image portability, since a given host directory can’t be guaranteed to be available on all hosts. For this reason, you can’t mount a host directory from within the Dockerfile. The VOLUME instruction does not support specifying a host-dir parameter. You must specify the mountpoint when you create or run the container.
也就是说我们在启动该镜像的时候必须覆盖该Volume mountpoint，如果不覆盖的话就会在/home/docker/volumes目录下生成一个默认的mountPoint， 对应于kubernetes，也就是我们必须手动指定volume来挂载到该目录上， 可以是emptyDir, PV等whatever只要覆盖就不会写到该默认的路径下面了。
如果不进行覆盖该mount point， 使用默认配置，则该匿名volume的生命周期对应于pod的生命周期，pod删除就会自动删除该volume，/home/docker/volumes下对应的数据也会删除。如果想在pod退出后还保存这部分数据的就应该小心了。
言归正传，对于这种inode耗尽的问题要想从本质上解决问题还是得限制每个pod/容器可以占用的inode数目， 但是目前大多数的container storage driver不支持inode隔离的， 还是得使用诸如deviceMapper这类基于块设备的存储插件比较合适， 还有就是单独给一些特殊的pod/容器，IO比较特殊的任务单独挂载一块磁盘（当然此处磁盘也可以是虚拟化出来的）， 避免相互影响。
2019.9 update:
社区issue: https://github.com/kubernetes/kubernetes/issues/52032
