在构建Kubernetes集群的时候我们使用到了一个名为Pause的镜像，这篇文章中我们来看一下在一个最基础的单元中Pause容器的使用状况。

事前准备：集群

本文使用Kubernetes 1.17.2，可参看下文进行快速环境搭建：

单机版本或者集群版本环境搭建

[root@host131 ansible]# kubectl get node -o wide
NAME              STATUS   ROLES    AGE     VERSION   INTERNAL-IP       EXTERNAL-IP   OS-IMAGE                KERNEL-VERSION          CONTAINER-RUNTIME
192.168.163.131   Ready    <none>   2m25s   v1.17.2   192.168.163.131   <none>        CentOS Linux 7 (Core)   3.10.0-957.el7.x86_64   docker://19.3.5
[root@host131 ansible]#

事前准备：Pod

使用如下Pod的YAML配置文件

[root@host131 Pod]# cat pod.yaml
---
apiVersion: v1
kind: Pod
metadata:name: testboxnamespace: default
spec:containers:- name: testbox-hostimage: busybox:latestcommand: ["sleep"]args: ["1000"]
...
[root@host131 Pod]#

创建并确认Pod信息

[root@host131 Pod]# kubectl create -f pod.yaml
pod/testbox created
[root@host131 Pod]#
[root@host131 Pod]# kubectl get pod -o wide
NAME      READY   STATUS    RESTARTS   AGE   IP             NODE              NOMINATED NODE   READINESS GATES
testbox   1/1     Running   0          8s    10.254.152.3   192.168.163.131   <none>           <none>
[root@host131 Pod]#
[root@host131 Pod]# kubectl describe pod testbox
Name:         testbox
Namespace:    default
Priority:     0
Node:         192.168.163.131/192.168.163.131
Start Time:   Sat, 08 Feb 2020 20:18:50 -0500
Labels:       <none>
Annotations:  <none>
Status:       Running
IP:           10.254.152.3
IPs:IP:  10.254.152.3
Containers:testbox-host:Container ID:  docker://de2eecac8a47ee6837cdd4915a1f2708366fe4b124611a4b2ac1469d9dd6924bImage:         busybox:latestImage ID:      docker-pullable://busybox@sha256:6915be4043561d64e0ab0f8f098dc2ac48e077fe23f488ac24b665166898115aPort:          <none>Host Port:     <none>Command:sleepArgs:1000State:          RunningStarted:      Sat, 08 Feb 2020 20:18:53 -0500Ready:          TrueRestart Count:  0Environment:    <none>Mounts:/var/run/secrets/kubernetes.io/serviceaccount from default-token-ljwn6 (ro)
Conditions:Type              StatusInitialized       True Ready             True ContainersReady   True PodScheduled      True
Volumes:default-token-ljwn6:Type:        Secret (a volume populated by a Secret)SecretName:  default-token-ljwn6Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300snode.kubernetes.io/unreachable:NoExecute for 300s
Events:Type    Reason     Age   From                      Message----    ------     ----  ----                      -------Normal  Scheduled  17s   default-scheduler         Successfully assigned default/testbox to 192.168.163.131Normal  Pulling    17s   kubelet, 192.168.163.131  Pulling image "busybox:latest"Normal  Pulled     14s   kubelet, 192.168.163.131  Successfully pulled image "busybox:latest"Normal  Created    14s   kubelet, 192.168.163.131  Created container testbox-hostNormal  Started    14s   kubelet, 192.168.163.131  Started container testbox-host
[root@host131 Pod]#

确认Pod的存在

使用docker ps命令以Pod名testbox为关键字进行搜索，可以看到除了BusyBox的容器之外还有一个pause的镜像，详细信息如下所示：

[root@host131 Pod]# docker ps |grep testbox
de2eecac8a47        busybox                                    "sleep 1000"             About a minute ago   Up About a minute                       k8s_testbox-host_testbox_default_1f0708d3-fe71-4668-b398-920d3278a546_0
4a39e1a37391        gcr.io/google_containers/pause-amd64:3.1   "/pause"                 About a minute ago   Up About a minute                       k8s_POD_testbox_default_1f0708d3-fe71-4668-b398-920d3278a546_0
[root@host131 Pod]#

pause容器和busybox的关联

对上述两个容器使用inspect命令，本文示例信息在下面的参考内容中全部贴出了，这里对其中的关联进行如下说明：

pause容器的ID（4a39e1a373912987af38d718c632ee0a184ec5470f37f840a76fc535fdfd1811）在busybox中NetworkMode和IpcMode等多处进行关联
HostConfig.Binds中pause容器未设定，而busybox中默认设定了service account的一些信息
CpuPeriod：pause容器被设定未0，而busybox设定为100000
环境变量Env与Labels等：pause容器中仅设定最基础的PATH，busybox在此基础上进行了设定，Labels等也类似
NetworkSettings：只在pause中设定，busybox不做设定。

整体说明：
pause作为Pod中第一个容器，它是为整个Pod提供网络基础设施设定的，所以整体的NetworkSettings中也只在pause容器中有所设定，而pause的Dockerfile也非常简单，它是一个from scratch的基础镜像。作为第一个启动的容器和Pid为1的进程，它所负责的内容和init比较类似，Pause主要负责如下内容：

包括基础网络设定的命名空间的共享（父子进程管理中，子进程会共享父进程的多种命名空前，在前面的文章中介绍过Linux的6种命令空间并进行过模拟，此处不再赘述）
负责僵尸进程的处理，在后续的源码解析中会进一步说明。

参考内容：inspect详细信息

pause容器的inspect信息

[root@host131 Pod]# docker inspect k8s_POD_testbox_default_1f0708d3-fe71-4668-b398-920d3278a546_0
[{"Id": "4a39e1a373912987af38d718c632ee0a184ec5470f37f840a76fc535fdfd1811","Created": "2020-02-09T01:18:50.407266072Z","Path": "/pause","Args": [],"State": {"Status": "running","Running": true,"Paused": false,"Restarting": false,"OOMKilled": false,"Dead": false,"Pid": 14657,"ExitCode": 0,"Error": "","StartedAt": "2020-02-09T01:18:50.684697657Z","FinishedAt": "0001-01-01T00:00:00Z"},"Image": "sha256:da86e6ba6ca197bf6bc5e9d900febd906b133eaa4750e6bed647b0fbe50ed43e","ResolvConfPath": "/var/lib/docker/containers/4a39e1a373912987af38d718c632ee0a184ec5470f37f840a76fc535fdfd1811/resolv.conf","HostnamePath": "/var/lib/docker/containers/4a39e1a373912987af38d718c632ee0a184ec5470f37f840a76fc535fdfd1811/hostname","HostsPath": "/var/lib/docker/containers/4a39e1a373912987af38d718c632ee0a184ec5470f37f840a76fc535fdfd1811/hosts","LogPath": "/var/lib/docker/containers/4a39e1a373912987af38d718c632ee0a184ec5470f37f840a76fc535fdfd1811/4a39e1a373912987af38d718c632ee0a184ec5470f37f840a76fc535fdfd1811-json.log","Name": "/k8s_POD_testbox_default_1f0708d3-fe71-4668-b398-920d3278a546_0","RestartCount": 0,"Driver": "overlay2","Platform": "linux","MountLabel": "","ProcessLabel": "","AppArmorProfile": "","ExecIDs": null,"HostConfig": {"Binds": null,"ContainerIDFile": "","LogConfig": {"Type": "json-file","Config": {"max-size": "1g"}},"NetworkMode": "default","PortBindings": {},"RestartPolicy": {"Name": "","MaximumRetryCount": 0},"AutoRemove": false,"VolumeDriver": "","VolumesFrom": null,"CapAdd": null,"CapDrop": null,"Capabilities": null,"Dns": null,"DnsOptions": null,"DnsSearch": null,"ExtraHosts": null,"GroupAdd": null,"IpcMode": "shareable","Cgroup": "","Links": null,"OomScoreAdj": -998,"PidMode": "","Privileged": false,"PublishAllPorts": false,"ReadonlyRootfs": false,"SecurityOpt": ["seccomp=unconfined"],"UTSMode": "","UsernsMode": "","ShmSize": 67108864,"Runtime": "runc","ConsoleSize": [0,0],"Isolation": "","CpuShares": 2,"Memory": 0,"NanoCpus": 0,"CgroupParent": "/kubepods/besteffort/pod1f0708d3-fe71-4668-b398-920d3278a546","BlkioWeight": 0,"BlkioWeightDevice": null,"BlkioDeviceReadBps": null,"BlkioDeviceWriteBps": null,"BlkioDeviceReadIOps": null,"BlkioDeviceWriteIOps": null,"CpuPeriod": 0,"CpuQuota": 0,"CpuRealtimePeriod": 0,"CpuRealtimeRuntime": 0,"CpusetCpus": "","CpusetMems": "","Devices": null,"DeviceCgroupRules": null,"DeviceRequests": null,"KernelMemory": 0,"KernelMemoryTCP": 0,"MemoryReservation": 0,"MemorySwap": 0,"MemorySwappiness": null,"OomKillDisable": false,"PidsLimit": null,"Ulimits": null,"CpuCount": 0,"CpuPercent": 0,"IOMaximumIOps": 0,"IOMaximumBandwidth": 0,"MaskedPaths": ["/proc/asound","/proc/acpi","/proc/kcore","/proc/keys","/proc/latency_stats","/proc/timer_list","/proc/timer_stats","/proc/sched_debug","/proc/scsi","/sys/firmware"],"ReadonlyPaths": ["/proc/bus","/proc/fs","/proc/irq","/proc/sys","/proc/sysrq-trigger"]},"GraphDriver": {"Data": {"LowerDir": "/var/lib/docker/overlay2/9aa12d8060b726b034c5c7828b38c05dff3d246c0886006931604188f1ae34d1-init/diff:/var/lib/docker/overlay2/92cf016f5ae66908dbca746c846be9d117d0a775f7f7d6ac59ced5f47811527f/diff","MergedDir": "/var/lib/docker/overlay2/9aa12d8060b726b034c5c7828b38c05dff3d246c0886006931604188f1ae34d1/merged","UpperDir": "/var/lib/docker/overlay2/9aa12d8060b726b034c5c7828b38c05dff3d246c0886006931604188f1ae34d1/diff","WorkDir": "/var/lib/docker/overlay2/9aa12d8060b726b034c5c7828b38c05dff3d246c0886006931604188f1ae34d1/work"},"Name": "overlay2"},"Mounts": [],"Config": {"Hostname": "testbox","Domainname": "","User": "","AttachStdin": false,"AttachStdout": false,"AttachStderr": false,"Tty": false,"OpenStdin": false,"StdinOnce": false,"Env": ["PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"],"Cmd": null,"Image": "gcr.io/google_containers/pause-amd64:3.1","Volumes": null,"WorkingDir": "","Entrypoint": ["/pause"],"OnBuild": null,"Labels": {"annotation.kubernetes.io/config.seen": "2020-02-08T20:18:50.092849465-05:00","annotation.kubernetes.io/config.source": "api","io.kubernetes.container.name": "POD","io.kubernetes.docker.type": "podsandbox","io.kubernetes.pod.name": "testbox","io.kubernetes.pod.namespace": "default","io.kubernetes.pod.uid": "1f0708d3-fe71-4668-b398-920d3278a546"}},"NetworkSettings": {"Bridge": "","SandboxID": "522acf2906641701cfcc6746769a3b989d3aff9ab3eb7056984ab8532f4f6326","HairpinMode": false,"LinkLocalIPv6Address": "","LinkLocalIPv6PrefixLen": 0,"Ports": {},"SandboxKey": "/var/run/docker/netns/522acf290664","SecondaryIPAddresses": null,"SecondaryIPv6Addresses": null,"EndpointID": "d522b1d76543bd1072c4e461e58b79a86433958c9c4fb2ad4b8317ddd21fbe4e","Gateway": "10.254.152.1","GlobalIPv6Address": "","GlobalIPv6PrefixLen": 0,"IPAddress": "10.254.152.3","IPPrefixLen": 21,"IPv6Gateway": "","MacAddress": "02:42:0a:fe:98:03","Networks": {"bridge": {"IPAMConfig": null,"Links": null,"Aliases": null,"NetworkID": "a0aaaf83254c57361b048203aa90422f4d150677fcdd606966f9b29e7a24b111","EndpointID": "d522b1d76543bd1072c4e461e58b79a86433958c9c4fb2ad4b8317ddd21fbe4e","Gateway": "10.254.152.1","IPAddress": "10.254.152.3","IPPrefixLen": 21,"IPv6Gateway": "","GlobalIPv6Address": "","GlobalIPv6PrefixLen": 0,"MacAddress": "02:42:0a:fe:98:03","DriverOpts": null}}}}
]
[root@host131 Pod]#

busybox容器的inspect信息

[root@host131 Pod]# docker inspect k8s_testbox-host_testbox_default_1f0708d3-fe71-4668-b398-920d3278a546_0
[{"Id": "de2eecac8a47ee6837cdd4915a1f2708366fe4b124611a4b2ac1469d9dd6924b","Created": "2020-02-09T01:18:53.164802631Z","Path": "sleep","Args": ["1000"],"State": {"Status": "exited","Running": false,"Paused": false,"Restarting": false,"OOMKilled": false,"Dead": false,"Pid": 0,"ExitCode": 0,"Error": "","StartedAt": "2020-02-09T01:18:53.266500495Z","FinishedAt": "2020-02-09T01:35:33.257185763Z"},"Image": "sha256:6d5fcfe5ff170471fcc3c8b47631d6d71202a1fd44cf3c147e50c8de21cf0648","ResolvConfPath": "/var/lib/docker/containers/4a39e1a373912987af38d718c632ee0a184ec5470f37f840a76fc535fdfd1811/resolv.conf","HostnamePath": "/var/lib/docker/containers/4a39e1a373912987af38d718c632ee0a184ec5470f37f840a76fc535fdfd1811/hostname","HostsPath": "/var/lib/kubelet/pods/1f0708d3-fe71-4668-b398-920d3278a546/etc-hosts","LogPath": "/var/lib/docker/containers/de2eecac8a47ee6837cdd4915a1f2708366fe4b124611a4b2ac1469d9dd6924b/de2eecac8a47ee6837cdd4915a1f2708366fe4b124611a4b2ac1469d9dd6924b-json.log","Name": "/k8s_testbox-host_testbox_default_1f0708d3-fe71-4668-b398-920d3278a546_0","RestartCount": 0,"Driver": "overlay2","Platform": "linux","MountLabel": "","ProcessLabel": "","AppArmorProfile": "","ExecIDs": null,"HostConfig": {"Binds": ["/var/lib/kubelet/pods/1f0708d3-fe71-4668-b398-920d3278a546/volumes/kubernetes.io~secret/default-token-ljwn6:/var/run/secrets/kubernetes.io/serviceaccount:ro","/var/lib/kubelet/pods/1f0708d3-fe71-4668-b398-920d3278a546/etc-hosts:/etc/hosts","/var/lib/kubelet/pods/1f0708d3-fe71-4668-b398-920d3278a546/containers/testbox-host/2c4f1a71:/dev/termination-log"],"ContainerIDFile": "","LogConfig": {"Type": "json-file","Config": {"max-size": "1g"}},"NetworkMode": "container:4a39e1a373912987af38d718c632ee0a184ec5470f37f840a76fc535fdfd1811","PortBindings": null,"RestartPolicy": {"Name": "no","MaximumRetryCount": 0},"AutoRemove": false,"VolumeDriver": "","VolumesFrom": null,"CapAdd": null,"CapDrop": null,"Capabilities": null,"Dns": null,"DnsOptions": null,"DnsSearch": null,"ExtraHosts": null,"GroupAdd": null,"IpcMode": "container:4a39e1a373912987af38d718c632ee0a184ec5470f37f840a76fc535fdfd1811","Cgroup": "","Links": null,"OomScoreAdj": 1000,"PidMode": "","Privileged": false,"PublishAllPorts": false,"ReadonlyRootfs": false,"SecurityOpt": ["seccomp=unconfined"],"UTSMode": "","UsernsMode": "","ShmSize": 67108864,"Runtime": "runc","ConsoleSize": [0,0],"Isolation": "","CpuShares": 2,"Memory": 0,"NanoCpus": 0,"CgroupParent": "/kubepods/besteffort/pod1f0708d3-fe71-4668-b398-920d3278a546","BlkioWeight": 0,"BlkioWeightDevice": null,"BlkioDeviceReadBps": null,"BlkioDeviceWriteBps": null,"BlkioDeviceReadIOps": null,"BlkioDeviceWriteIOps": null,"CpuPeriod": 100000,"CpuQuota": 0,"CpuRealtimePeriod": 0,"CpuRealtimeRuntime": 0,"CpusetCpus": "","CpusetMems": "","Devices": [],"DeviceCgroupRules": null,"DeviceRequests": null,"KernelMemory": 0,"KernelMemoryTCP": 0,"MemoryReservation": 0,"MemorySwap": 0,"MemorySwappiness": null,"OomKillDisable": false,"PidsLimit": null,"Ulimits": null,"CpuCount": 0,"CpuPercent": 0,"IOMaximumIOps": 0,"IOMaximumBandwidth": 0,"MaskedPaths": ["/proc/acpi","/proc/kcore","/proc/keys","/proc/latency_stats","/proc/timer_list","/proc/timer_stats","/proc/sched_debug","/proc/scsi","/sys/firmware"],"ReadonlyPaths": ["/proc/asound","/proc/bus","/proc/fs","/proc/irq","/proc/sys","/proc/sysrq-trigger"]},"GraphDriver": {"Data": {"LowerDir": "/var/lib/docker/overlay2/c2985676cea73d146f7911bff0830cf68a5a8e6be0dffa257e5c191350a3862d-init/diff:/var/lib/docker/overlay2/72c2db679958db531aab82d9c11c4e9397697a2f03b011a8e3e35b165e37d641/diff","MergedDir": "/var/lib/docker/overlay2/c2985676cea73d146f7911bff0830cf68a5a8e6be0dffa257e5c191350a3862d/merged","UpperDir": "/var/lib/docker/overlay2/c2985676cea73d146f7911bff0830cf68a5a8e6be0dffa257e5c191350a3862d/diff","WorkDir": "/var/lib/docker/overlay2/c2985676cea73d146f7911bff0830cf68a5a8e6be0dffa257e5c191350a3862d/work"},"Name": "overlay2"},"Mounts": [{"Type": "bind","Source": "/var/lib/kubelet/pods/1f0708d3-fe71-4668-b398-920d3278a546/volumes/kubernetes.io~secret/default-token-ljwn6","Destination": "/var/run/secrets/kubernetes.io/serviceaccount","Mode": "ro","RW": false,"Propagation": "rprivate"},{"Type": "bind","Source": "/var/lib/kubelet/pods/1f0708d3-fe71-4668-b398-920d3278a546/etc-hosts","Destination": "/etc/hosts","Mode": "","RW": true,"Propagation": "rprivate"},{"Type": "bind","Source": "/var/lib/kubelet/pods/1f0708d3-fe71-4668-b398-920d3278a546/containers/testbox-host/2c4f1a71","Destination": "/dev/termination-log","Mode": "","RW": true,"Propagation": "rprivate"}],"Config": {"Hostname": "testbox","Domainname": "","User": "0","AttachStdin": false,"AttachStdout": false,"AttachStderr": false,"Tty": false,"OpenStdin": false,"StdinOnce": false,"Env": ["KUBERNETES_SERVICE_PORT_HTTPS=443","KUBERNETES_PORT=tcp://10.254.0.1:443","KUBERNETES_PORT_443_TCP=tcp://10.254.0.1:443","KUBERNETES_PORT_443_TCP_PROTO=tcp","KUBERNETES_PORT_443_TCP_PORT=443","KUBERNETES_PORT_443_TCP_ADDR=10.254.0.1","KUBERNETES_SERVICE_HOST=10.254.0.1","KUBERNETES_SERVICE_PORT=443","PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"],"Cmd": ["1000"],"Healthcheck": {"Test": ["NONE"]},"Image": "busybox@sha256:6915be4043561d64e0ab0f8f098dc2ac48e077fe23f488ac24b665166898115a","Volumes": null,"WorkingDir": "","Entrypoint": ["sleep"],"OnBuild": null,"Labels": {"annotation.io.kubernetes.container.hash": "58ac6600","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/default_testbox_1f0708d3-fe71-4668-b398-920d3278a546/testbox-host/0.log","io.kubernetes.container.name": "testbox-host","io.kubernetes.docker.type": "container","io.kubernetes.pod.name": "testbox","io.kubernetes.pod.namespace": "default","io.kubernetes.pod.uid": "1f0708d3-fe71-4668-b398-920d3278a546","io.kubernetes.sandbox.id": "4a39e1a373912987af38d718c632ee0a184ec5470f37f840a76fc535fdfd1811"}},"NetworkSettings": {"Bridge": "","SandboxID": "","HairpinMode": false,"LinkLocalIPv6Address": "","LinkLocalIPv6PrefixLen": 0,"Ports": {},"SandboxKey": "","SecondaryIPAddresses": null,"SecondaryIPv6Addresses": null,"EndpointID": "","Gateway": "","GlobalIPv6Address": "","GlobalIPv6PrefixLen": 0,"IPAddress": "","IPPrefixLen": 0,"IPv6Gateway": "","MacAddress": "","Networks": {}}}
]
[root@host131 Pod]#

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