容器技术

发布日期: 2019-07-10

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：

[root@node01 ~]# docker ps
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

### 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

#include <stdio.h>
#include <unistd.h>

int main() {
  pid_t pid;
  pid = fork();
  if (pid == 0) {
    while (getppid() > 1)
      ;
    printf("Child exiting: pid=%d ppid=%d\n", getpid(), getppid());
    return 0;
  } else if (pid > 0) {
    printf("Parent exiting: pid=%d ppid=%d\n", getpid(), getppid());
    return 0;
  }
  perror("Could not create child");
  return 1;
}

pause.c文件

#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 %s\n", 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 process\n");

  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 terminated\n");
  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：

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

.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

ifeq ($(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 $@"

根据上面的启动容器，来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 $@

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：

# 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：

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

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。

[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