kubernetes集群中的pause容器

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：

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[root@node01 ~] CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 43884d79fe6f nginx "nginx -g 'daemon of…" 11 hours ago Up 11 hours k8s_nginx-pod_nginx-con-594b8d6b48-46gf7_default_25b0048f -a24f-11e9-8149-00163e0134cf_0 eff67394c9c8 nginx "nginx -g 'daemon of…" 11 hours ago Up 11 hours k8s_nginx-pod_nginx-con-594b8d6b48-vt589_default_25aefc99 -a24f-11e9-8149-00163e0134cf_1 261226f6b92a 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 ```bash cat >/etc/systemd/system/kubelet.service <<EOF [Unit] Description=Kubernetes Kubelet Documentation=https://github.com/GoogleCloudPlatform/kubernetes After=docker.service Requires=docker.service [Service] WorkingDirectory=/var/lib/kubelet ExecStart=/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=2 Restart=on-failure RestartSec=5 [Install] WantedBy=multi-user.target EOF

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 #endif static 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：

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FROM scratch ARG ARCH ADD bin/pause- ${ARCH} /pause ENTRYPOINT [ "/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-manifest include ../../hack/make-rules/Makefile.manifest REGISTRY ?= staging-k8s.gcr.io IMAGE = $(REGISTRY)/pause IMAGE_WITH_ARCH = $(IMAGE)-$(ARCH) TAG = 3.1 REV = $(shell git describe --contains --always --match= 'v*') # Architectures supported: amd64, arm, arm64, ppc64le and s390x ARCH ?= amd64 ALL_ARCH = amd64 arm arm64 ppc64le s390x CFLAGS = -Os -Wall -Werror -static -DVERSION=v$(TAG)-$(REV) KUBE_CROSS_IMAGE ?= k8s.gcr.io/kube-cross KUBE_CROSS_VERSION ?= $(shell cat ../build-image/cross/VERSION) BIN = pause SRCS = pause.c ife 大专栏   kubernetes集群中的pause容器q ($(ARCH),amd64) TRIPLE ?= x86_64-linux-gnu endif ifeq ($(ARCH),arm) TRIPLE ?= arm-linux-gnueabihf endif ifeq ($(ARCH),arm64) TRIPLE ?= aarch64-linux-gnu endif ifeq ($(ARCH),ppc64le) TRIPLE ?= powerpc64le-linux-gnu endif ifeq ($(ARCH),s390x) TRIPLE ?= s390x-linux-gnu endif # If you want to build AND push all containers, see the 'all-push' rule. all: all-container all-push: all-push-images push-manifest push-manifest: manifest-tool manifest-tool push from-args --platforms $(call join_platforms,$(ALL_ARCH)) --template $(IMAGE)-ARCH:$(TAG) --target $(IMAGE):$(TAG) sub-container-%: $(MAKE) ARCH=$* container sub-push-%: $(MAKE) ARCH=$* push all-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 ```bash 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 $@"

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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 $@ # Useful for testing, not automatically included in container image orphan: bin/orphan-$(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：

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# Architectures supported: amd64, arm, arm64, ppc64le and s390x ARCH ?= amd64 ALL_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.io IMAGE = $(REGISTRY)/pause IMAGE_WITH_ARCH = $(IMAGE)-$(ARCH) TAG = 3.1 ARCH ?= amd64 BIN = pause SRCS = pause.c REV = $(shell git describe --contains --always --match= 'v*') CFLAGS = -Os -Wall -Werror -static -DVERSION=v$(TAG)-$(REV) KUBE_CROSS_IMAGE ?= k8s.gcr.io/kube-cross KUBE_CROSS_VERSION ?= $(shell cat ../build-image/cross/VERSION) ifeq ($(ARCH),amd64) TRIPLE ?= x86_64-linux-gnu build: 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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[root@harbor1 ~] # docker run -idt --name pause-ceshi cntsp/pause:3.1 ce2a4ffccf1d2b190b9f8cc45f6e4912f278aa7a55280ce8a69433e5345e5816 [root@harbor1 ~] # 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'. [root@harbor1 ~] # docker run -idt --name busybox11 --net=container:pause-ceshi --pid=container:pause-ceshi --ipc=container:pause-ceshi busybox Unable to find image 'busybox:latest' locally latest: Pulling from library/busybox 8e674ad76dce: Pull complete Digest: sha256:c94cf1b87ccb80f2e6414ef913c748b105060debda482058d2b8d0fce39f11b9 Status: Downloaded newer image for busybox:latest 6bec8c69198eaa444580ccaa0a50afbc16a51eea489fa7e81729d535cb691ea6 [root@harbor1 ~] # docker ps -a CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 6bec8c69198e busybox "sh" bout a minute ago Up About a minute busybox11 ce2a4ffccf1d cntsp/pause:3.1 "/pause" 2 minutes ago Up 2 minutes pause-ceshi [root@harbor1 ~] # 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 [root@harbor1 ~] # 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