昨天晚上搭建好了k8s多主集群，启动了一个nginx的pod，然而每启动一个pod就伴随这一个pause容器，考虑到之前在做kubelet的systemd unit文件时有见到：

[ ~]CONTAINER ID    IMAGE                                                                 COMMAND                  CREATED             STATUS        PORTS    NAMES43884d79fe6f    nginx                                                                 "nginx -g 'daemon of…"   11 hours ago        Up 11 hours            k8s_nginx-pod_nginx-con-594b8d6b48-46gf7_default_25b0048f-a24f-11e9-8149-00163e0134cf_0eff67394c9c8    nginx                                                                 "nginx -g 'daemon of…"   11 hours ago        Up 11 hours            k8s_nginx-pod_nginx-con-594b8d6b48-vt589_default_25aefc99-a24f-11e9-8149-00163e0134cf_1261226f6b92a    registry.cn-hangzhou.aliyuncs.com/google_containers/pause-amd64:3.1   "/pause"                 11 hours ago        Up 11 hours            k8s_POD_nginx-con-594b8d6b48-vt589_default_25aefc99-a24f-11e9-8149-00163e0134cf_1
fc94013b93dd    registry.cn-hangzhou.aliyuncs.com/google_containers/pause-amd64:3.1   "/pause"                 11 hours ago        Up 11 hours            k8s_POD_nginx-con-594b8d6b48-46gf7_default_25b0048f-a24f-11e9-8149-00163e0134cf_1

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### 6 	创建和分发kubelet systemd unit文件```bashcat >/etc/systemd/system/kubelet.service <<EOF[Unit]Description=Kubernetes KubeletDocumentation=https://github.com/GoogleCloudPlatform/kubernetesAfter=docker.serviceRequires=docker.service[Service]WorkingDirectory=/var/lib/kubeletExecStart=/usr/local/bin/kubelet   --bootstrap-kubeconfig=/etc/kubernetes/cert/kubelet-bootstrap.kubeconfig   --cert-dir=/etc/kubernetes/cert   --kubeconfig=/etc/kubernetes/cert/kubelet.kubeconfig   --config=/etc/kubernetes/cert/kubelet.config.json   --hostname-override=172.24.150.89   --pod-infra-container-image=registry.cn-hangzhou.aliyuncs.com/google_containers/pause-amd64:3.1   --allow-privileged=true   --alsologtostderr=true   --logtostderr=false   --log-dir=/var/log/kubernetes   --v=2Restart=on-failureRestartSec=5[Install]WantedBy=multi-user.targetEOF

首先找一下源码看一下：
pause源码C语言编写的主要有四个文件：
orphan.c文件

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#include <stdio.h>#include <unistd.h>int () {  pid_t pid;  pid = fork();  if (pid == 0) {    while (getppid() > 1)      ;    printf("Child exiting: pid=%d ppid=%dn", getpid(), getppid());    return 0;  } else if (pid > 0) {    printf("Parent exiting: pid=%d ppid=%dn", getpid(), getppid());    return 0;  }  perror("Could not create child");  return 1;}

pause.c文件

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#include <signal.h>#include <stdio.h>#include <stdlib.h>#include <string.h>#include <sys/types.h>#include <sys/wait.h>#include <unistd.h>#define STRINGIFY(x) #x#define VERSION_STRING(x) STRINGIFY(x)#ifndef VERSION#define VERSION HEAD#endifstatic void sigdown(int signo) {  psignal(signo, "Shutting down, got signal");  exit(0);}static void sigreap(int signo) {  while (waitpid(-1, NULL, WNOHANG) > 0)    ;}int main(int argc, char **argv) {  int i;  for (i = 1; i < argc; ++i) {    if (!strcasecmp(argv[i], "-v")) {      printf("pause.c %sn", VERSION_STRING(VERSION));      return 0;    }  }  if (getpid() != 1)    /* Not an error because pause sees use outside of infra containers. */    fprintf(stderr, "Warning: pause should be the first processn");  if (sigaction(SIGINT, &(struct sigaction){.sa_handler = sigdown}, NULL) < 0)    return 1;  if (sigaction(SIGTERM, &(struct sigaction){.sa_handler = sigdown}, NULL) < 0)    return 2;  if (sigaction(SIGCHLD, &(struct sigaction){.sa_handler = sigreap,                                             .sa_flags = SA_NOCLDSTOP},                NULL) < 0)    return 3;  for (;;)    pause();  fprintf(stderr, "Error: infinite loop terminatedn");  return 42;}

至于里面写的啥，我也看不懂，pose出来让你们看看哈！
Makefile文件用于制作pause镜像，制作镜像的模板是Dockerfile，首先看这个Dockerfile(去除注释)文件：

1234	FROM scratchARG ARCHADD bin/pause-${ARCH} /pauseENTRYPOINT ["/pause"]

FROM scratch: 基础镜像是一个空镜像(an explicity empty image)
ARG ARCH: 等待在docker-build -build-arg时提供的ARCH参数
ADD bin/pause-$(ARCH)/pause: 添加外部文件到内部
ENTRYPOINT[“/pause”]: 开启容器，运行命令
中间两部非常重要，至于如何实现的不懂哦？

pause的Makefile

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.PHONY: all push container clean orphan all-push push-manifestinclude ../../hack/make-rules/Makefile.manifestREGISTRY ?= staging-k8s.gcr.ioIMAGE = $(REGISTRY)/pauseIMAGE_WITH_ARCH = $(IMAGE)-$(ARCH)TAG = 3.1REV = $(shell git describe --contains --always --match='v*')# Architectures supported: amd64, arm, arm64, ppc64le and s390xARCH ?= amd64ALL_ARCH = amd64 arm arm64 ppc64le s390xCFLAGS = -Os -Wall -Werror -static -DVERSION=v$(TAG)-$(REV)KUBE_CROSS_IMAGE ?= k8s.gcr.io/kube-crossKUBE_CROSS_VERSION ?= $(shell cat ../build-image/cross/VERSION)BIN = pauseSRCS = pause.cife 大专栏  kubernetes集群中的pause容器q ($(ARCH),amd64)	TRIPLE ?= x86_64-linux-gnuendififeq ($(ARCH),arm)	TRIPLE ?= arm-linux-gnueabihfendififeq ($(ARCH),arm64)	TRIPLE ?= aarch64-linux-gnuendififeq ($(ARCH),ppc64le)	TRIPLE ?= powerpc64le-linux-gnuendififeq ($(ARCH),s390x)	TRIPLE ?= s390x-linux-gnuendif# If you want to build AND push all containers, see the 'all-push' rule.all: all-containerall-push: all-push-images push-manifestpush-manifest: manifest-tool	manifest-tool push from-args --platforms $(call join_platforms,$(ALL_ARCH)) --template $(IMAGE)-ARCH:$(TAG) --target $(IMAGE):$(TAG)sub-container-%:	$(MAKE) ARCH=$* containersub-push-%:	$(MAKE) ARCH=$* pushall-container: $(addprefix sub-container-,$(ALL_ARCH))all-push-images: $(addprefix sub-push-,$(ALL_ARCH))build: bin/$(BIN)-$(ARCH)# 先启动一个容器```bashbin/$(BIN)-$(ARCH): $(SRCS)	mkdir -p bin	docker run --rm -u $$(id -u):$$(id -g) -v $$(pwd):/build 		$(KUBE_CROSS_IMAGE):$(KUBE_CROSS_VERSION) 		/bin/bash -c "
			cd /build && 			$(TRIPLE)-gcc $(CFLAGS) -o  $^ && 			$(TRIPLE)-strip "

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container: .container-$(ARCH).container-$(ARCH): bin/$(BIN)-$(ARCH)	docker build --pull -t $(IMAGE_WITH_ARCH):$(TAG) --build-arg ARCH=$(ARCH) .	touch 
push: .push-$(ARCH).push-$(ARCH): .container-$(ARCH)	docker push $(IMAGE_WITH_ARCH):$(TAG)	touch 
# Useful for testing, not automatically included in container imageorphan: bin/orphan-$(ARCH)bin/orphan-$(ARCH): orphan.c	mkdir -p bin	docker run -u $$(id -u):$$(id -g) -v $$(pwd):/build 		$(KUBE_CROSS_IMAGE):$(KUBE_CROSS_VERSION) 		/bin/bash -c "
			cd /build && 			$(TRIPLE)-gcc $(CFLAGS) -o  $^ && 			$(TRIPLE)-strip "clean:	rm -rf .container-* .push-* bin/

ARCH值：

1234	# Architectures supported: amd64, arm, arm64, ppc64le and s390xARCH ?= amd64ALL_ARCH = amd64 arm arm64 ppc64le s390x

可以看出支持很多架构类型，默认为amd64

制作pause镜像的过程如下：

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REGISTRY ?= staging-k8s.gcr.ioIMAGE = $(REGISTRY)/pauseIMAGE_WITH_ARCH = $(IMAGE)-$(ARCH)TAG = 3.1ARCH ?= amd64BIN = pauseSRCS = pause.cREV = $(shell git describe --contains --always --match='v*')CFLAGS = -Os -Wall -Werror -static -DVERSION=v$(TAG)-$(REV)KUBE_CROSS_IMAGE ?= k8s.gcr.io/kube-crossKUBE_CROSS_VERSION ?= $(shell cat ../build-image/cross/VERSION)ifeq ($(ARCH),amd64)	TRIPLE ?= x86_64-linux-gnubuild: bin/$(BIN)-$(ARCH)# 启动一个容器bin/$(BIN)-$(ARCH): $(SRCS)	mkdir -p bin	docker run --rm -u $$(id -u):$$(id -g) -v $$(pwd):/build 		$(KUBE_CROSS_IMAGE):$(KUBE_CROSS_VERSION) 		/bin/bash -c "
			cd /build && 			$(TRIPLE)-gcc $(CFLAGS) -o  $^ && 			$(TRIPLE)-strip "# build一个pause镜像container: .container-$(ARCH).container-$(ARCH): bin/$(BIN)-$(ARCH)	docker build --pull -t $(IMAGE_WITH_ARCH):$(TAG) --build-arg ARCH=$(ARCH) .	touch

$(KUBE_CROSS_IMAGE):$(KUBE_CROSS_VERSION)=k8s.gcr.io/kube-cross:v1.12.6-1

启动一个容器

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bin/pause-amd64:pause.c	mkdir -p bin	docker run --rm -u $$(id -u):$$(id -g) -v $$(pwd):/build 		k8s.gcr.io/kube-cross:v1.12.6-1 		/bin/bash -c "
			cd /build && 			x86_64-linux-gnu-gcc v3.1-$(REV) -o  $^ && 			x86_64-linux-gnu-strip "# build一个pause镜像container: .container-amd64.container-amd64: bin/pause-amd64	docker build --pull -t staging-k8s.gcr.io/pause-amd64:3.1 --build-arg ARCH=amd64 .

至于详细的构建过程，我就不写了，我看不懂呀！

pause容器的工作
可知kubernetes的pod抽象基于Linux的namespace和cgroups，为容器提供了良好的隔离环境。在同一个pod中，不同容器犹如在localhost中。

在Unix系统中，PID为1的进程为init进程，即所有进程的父进程。它很特殊，维护一张进程表，不断地检查进程状态。例如，一旦某个子进程由于父进程的错误而变成了“孤儿进程”，其便会被init进程进行收养并最终回收资源，从而结束进程。

或者，某子进程已经停止但进程表中仍然存在该进程，因为其父进程未进行wait syscall进行索引，从而该进程变成“僵尸进程”，这种僵尸进程存在时间较短。不过如果父进程只wait，而未syscall的话，僵尸进程便会存在较长时间。

同时，init进程不能处理某个信号逻辑，拥有“信号屏蔽”功能，从而防止init进程被误杀。

容器中使用pid namespace来对pid进行隔离，从而每个容器中均有其独立的init进程。例如对于寄主机上可以用个发送SIGKILL或者SIGSTOP(也就是docker kill 或者docker stop)来强制终止容器的运行，即终止容器内的init进程。一旦init进程被销毁，同一pid namespace下的进程也随之被销毁，并容器进程被回收相应资源。

kubernetes中的pause容器便被设计成为每个业务容器提供以下功能：
在pod中担任Linux命名空间共享的基础；
启用pid命名空间，开启init进程。

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[ ~]# docker run -idt --name pause-ceshi cntsp/pause:3.1 
ce2a4ffccf1d2b190b9f8cc45f6e4912f278aa7a55280ce8a69433e5345e5816[ ~]# docker run -idt --name busybox11 --net=container:pause11 --pid=container:pause11 --ipc=container:pause11 busybox
docker: Error response from daemon: No such container: pause11.See 'docker run --help'.[ ~]# docker run -idt --name busybox11 --net=container:pause-ceshi --pid=container:pause-ceshi --ipc=container:pause-ceshi busybox
Unable to find image 'busybox:latest' locallylatest: Pulling from library/busybox8e674ad76dce: Pull complete Digest: sha256:c94cf1b87ccb80f2e6414ef913c748b105060debda482058d2b8d0fce39f11b9Status: Downloaded newer image for busybox:latest6bec8c69198eaa444580ccaa0a50afbc16a51eea489fa7e81729d535cb691ea6[ ~]# docker ps -a 
CONTAINER ID        IMAGE                                          COMMAND             CREATED             STATUS                PORTS                          NAMES6bec8c69198e        busybox                                        "sh"                bout a minute ago   Up About a minute                                    busybox11ce2a4ffccf1d        cntsp/pause:3.1                                "/pause"            2 minutes ago       Up 2 minutes                                         pause-ceshi[ ~]# docker exec -it busybox11 /bin/bash
OCI runtime exec failed: exec failed: container_linux.go:348: starting container process caused "exec: "/bin/bash": stat /bin/bash: no such file or directory": unknown[ ~]# docker exec -it busybox11 /bin/sh
/ # ps aux
PID   USER     TIME  COMMAND    1 root      0:00 /pause    6 root      0:00 sh   16 root      0:00 /bin/sh   21 root      0:00 ps aux/ # 
这里补充一点：Docker网络模式：其中有一种是Container:			> * 复用其它容器的网络Container模式：	>	* 重用另一个容器的Network Namespace,新创建的容器不会创建网卡，配置IP	>	* 和一个指定的容器共享IP、端口范围	>	* 两个容器除了网络方面，其它的如文件系统、进程列表等还是隔离的，两个容器的进程可以通过lo网卡设备通信。	>	* Pod里的Pause容器和Pod里的其它容器就是此种网络

kubernetes集群中的pause容器

启动一个容器

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