加载kind镜像

Docker镜像可以通过以下命令加载到集群中:

kind load docker-image my-custom-image --name cluster-name

此外,镜像打包也可以加载:

kind load image-archive /my-image-archive.tar

kind镜像加载实战

kind提供了将docker镜像加载到集群每个node节点上的操作命令,加载镜像之后,集群的每个节点都会具备该镜像文件,就不需要再从docker hub仓库pull了,节约了下载带宽资源。当然,你使用kubectl命令创建pod也能够下载对应镜像,重复拉取镜像会拖慢pod创建速度。

注解

这里采用的镜像实战是 从Dockerfile构建Docker镜像 案例,我们将在kind集群中构架一个基础的自定义ssh服务的CentOS。

  • 创建Dockerfile目录 docker ,然后进入该目录,在该目录下存放 centos8-ssh 文件
../admin/centos8-ssh
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# Build centos 8 image with ssh:
# ------------------------------
# docker build -f centos8-ssh -t local:centos8-ssh

# create container:
# -----------------
# docker run -itd -p 1122:22 --hostname myserver --name myserver local:centos8-ssh

# create container with volume:
# -----------------------------
# docker volume create data
# docker run -itd -p 1122:22 --hostname myserver --name myserver -v data:/data local:centos8-ssh

# create container with volume and static ip:
# -------------------------------------------
# docker volume create data
# docker network create --subnet=172.18.0.0/16 data-net
# docker run -itd -p 1122:22 --hostname myserver --name myserver -v data:/data \
#   --net data-net --ip 172.18.0.252 local:centos8-ssh

# create container with volume and static ip, then limit resource and map port:
# -----------------------------------------------------------------------------
# docker volume create data
# docker network create --subnet=172.18.0.0/16 data-net
# docker run -itd -p 1122:22 --hostname myserver --name myserver -v data:/data \
#   --net data-net --ip 172.18.0.252 --memory=2048M --cpus="1.5" \
#   -p 22 -p 8080:80 local:centos8-ssh

FROM docker.io/centos:8
MAINTAINER vincent huatai <vincent@huatai.me>

RUN dnf clean all
RUN dnf -y update

RUN dnf -y install which sudo openssh-clients openssh-server initscripts

# Prepare sshd host key
RUN ssh-keygen -A

# add account "admin" and give sudo privilege
RUN groupadd -g 505 admin
RUN useradd -g 505 -u 505 -d /home/admin -m admin
RUN usermod -aG wheel admin
RUN echo "%wheel        ALL=(ALL)       NOPASSWD: ALL" >> /etc/sudoers

# Add ssh public key for login
RUN mkdir -p /home/admin/.ssh
COPY authorized_keys /home/admin/.ssh/authorized_keys
RUN chown -R admin:admin /home/admin/.ssh
RUN chmod 600 /home/admin/.ssh/authorized_keys
RUN chmod 700 /home/admin/.ssh
RUN mv /var/run/nologin /var/run/nologin.bak

# run service when container started - sshd
EXPOSE 22:1122
#CMD ["/usr/sbin/sshd", "-D"]

# ----------
# WANT run sshd and get a bash
# ENTRYPOINT will not be override by commandline
# ----------
ENTRYPOINT /usr/sbin/sshd && /bin/bash

注解

如果你有需要复制到镜像中文件,例如我需要复制公钥文件 authorized_keys

  • 执行docker创建镜像命令:

    docker build -f centos8-ssh -t local:centos8-ssh .
    
  • 完成后检查镜像:

    docker images
    

显示:

REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
local               centos8-ssh         80314bfa9eed        8 seconds ago       286MB
  • 将镜像加载到集群 dev 中:

    kind load docker-image local:centos8-ssh --name dev
    

提示信息:

Image: "local:centos8-ssh" with ID "sha256:80314bfa9eeddd87d002cf89026089a084b9fd2e511bbc07f0fbc977e7f06ed3" not yet present on node "dev-worker2", loading...
Image: "local:centos8-ssh" with ID "sha256:80314bfa9eeddd87d002cf89026089a084b9fd2e511bbc07f0fbc977e7f06ed3" not yet present on node "dev-worker", loading...
...
  • 完成镜像上传后,kind集群的每个node节点都会具备分发的自定义镜像 centos8-ssh ,我们需要检查镜像的名字, docker exec 提供了检查集群节点(这里案例是检查集群节点 dev-worker )上镜像列表的命令:

    docker exec -it dev-worker crictl images
    

显示镜像列表如下:

MAGE                                      TAG                 IMAGE ID            SIZE
docker.io/kindest/kindnetd                 0.5.4               2186a1a396deb       113MB
docker.io/library/local                    centos8-ssh         80314bfa9eedd       294MB
docker.io/rancher/local-path-provisioner   v0.0.12             db10073a6f829       42MB
k8s.gcr.io/coredns                         1.6.7               67da37a9a360e       43.9MB
k8s.gcr.io/debian-base                     v2.0.0              9bd6154724425       53.9MB
k8s.gcr.io/etcd                            3.4.3-0             303ce5db0e90d       290MB
k8s.gcr.io/kube-apiserver                  v1.18.2             7df05884b1e25       147MB
k8s.gcr.io/kube-controller-manager         v1.18.2             31fd71c85722f       133MB
k8s.gcr.io/kube-proxy                      v1.18.2             312d3d1cb6c72       133MB
k8s.gcr.io/kube-scheduler                  v1.18.2             121edc8356c58       113MB
k8s.gcr.io/pause                           3.2                 80d28bedfe5de       686kB

注解

crictl 是CRI兼容的容器runtime命令行工具。在kind的Kubernetes集群节点上没有安装docker命令行工具,而是安装了Kubernetes的crictl工具。

注意,kind配置的 /etc/crictl.yaml 只有一行配置,指向Kubernetes节点上的containerd的socket:

runtime-endpoint: unix:///var/run/containerd/containerd.sock

从节点上运行的 kubelet 进程的参数也可以看到 --container-runtime-endpoint=/run/containerd/containerd.sock ,这就是 crictl 可以直接和 containerd 通讯的socks。

  • 为了方便管理,我先创建一个独立的namespace,名为 studio 来容纳后续创建的pod:

    kubectl create namespace studio
    

提示信息:

namespace/studio created

检查:

kubectl get namespaces

可以看到:

NAME                 STATUS   AGE
default              Active   2d
kube-node-lease      Active   2d
kube-public          Active   2d
kube-system          Active   2d
local-path-storage   Active   2d
studio               Active   16s
  • 既然我们已经加载好镜像(注意:创建的docker镜像是具备了 ENTRYPOINT ,也就是最后会自动启动sshd和bash,所以我们的kubernetes不需要传递容器命令),我们现在来创建pod:

    kubectl run dev-studio --image docker.io/library/local:centos8-ssh --namespace=studio
    
  • 然后检查创建的pod:

    kubectl get pods -n studio
    

糟糕,pod出现了crash:

NAME         READY   STATUS             RESTARTS   AGE
dev-studio   0/1     CrashLoopBackOff   3          59s

我们来检查以下pod失败的原因:

kubectl describe pods dev-studio -n studio

输出显示:

Name:         dev-studio
Namespace:    studio
Priority:     0
Node:         dev-worker3/172.19.0.4
Start Time:   Sun, 19 Jul 2020 22:36:23 +0800
Labels:       run=dev-studio
Annotations:  <none>
Status:       Running
IP:           10.244.5.2
IPs:
  IP:  10.244.5.2
Containers:
  dev-studio:
    Container ID:   containerd://50e1df5e4464ede9f6cdb0e3b59bb5bcf93c02907cf0038732a0ff8fcfe882c2
    Image:          docker.io/library/local:centos8-ssh
    Image ID:       sha256:80314bfa9eeddd87d002cf89026089a084b9fd2e511bbc07f0fbc977e7f06ed3
    Port:           <none>
    Host Port:      <none>
    State:          Terminated
      Reason:       Completed
      Exit Code:    0
      Started:      Sun, 19 Jul 2020 22:37:56 +0800
      Finished:     Sun, 19 Jul 2020 22:37:56 +0800
    Last State:     Terminated
      Reason:       Completed
      Exit Code:    0
      Started:      Sun, 19 Jul 2020 22:37:06 +0800
      Finished:     Sun, 19 Jul 2020 22:37:06 +0800
    Ready:          False
    Restart Count:  4
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-tpblw (ro)
Conditions:
  Type              Status
  Initialized       True
  Ready             False
  ContainersReady   False
  PodScheduled      True
Volumes:
  default-token-tpblw:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-tpblw
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type     Reason     Age               From                  Message
  ----     ------     ----              ----                  -------
  Normal   Scheduled  <unknown>         default-scheduler     Successfully assigned studio/dev-studio to dev-worker3
  Normal   Pulled     2s (x5 over 94s)  kubelet, dev-worker3  Container image "docker.io/library/local:centos8-ssh" already present on machine
  Normal   Created    2s (x5 over 94s)  kubelet, dev-worker3  Created container dev-studio
  Normal   Started    2s (x5 over 94s)  kubelet, dev-worker3  Started container dev-studio
  Warning  BackOff    1s (x9 over 92s)  kubelet, dev-worker3  Back-off restarting failed container

排查pod启动失败

  • 登陆到服务器节点排查:

    docker exec -it dev-worker3 /bin/bash
    
  • 在node节点 dev-worker3 上通过 crictl 排查,首先检查pods:

    crictl pods
    

这里显示的信息是Ready的:

POD ID              CREATED             STATE               NAME                NAMESPACE           ATTEMPT
23e53447b90b3       13 minutes ago      Ready               dev-studio          studio              0
f4b1796209a86       2 days ago          Ready               kube-proxy-qfrkl    kube-system         0
2ef62989002ca       2 days ago          Ready               kindnet-ktjzr       kube-system         0

但是容器启动失败:

crictl ps -a
CONTAINER           IMAGE               CREATED             STATE               NAME                ATTEMPT             POD ID
375a0e4fa36a8       80314bfa9eedd       25 seconds ago      Exited              dev-studio          8                   23e53447b90b3
b8de653dd80ff       2186a1a396deb       2 days ago          Running             kindnet-cni         0                   2ef62989002ca
44b9a685912b6       312d3d1cb6c72       2 days ago          Running             kube-proxy          0                   f4b1796209a86
  • 检查容器日志:

    crictl logs 375a0e4fa36a8
    

奇怪,日志始终是空的

  • 在node上inspect容器:

    crictl inspect 375a0e4fa36a8
    

显示:

...
    "runtimeSpec": {
      "ociVersion": "1.0.1-dev",
      "process": {
        "user": {
          "uid": 0,
          "gid": 0
        },
        "args": [
          "/bin/sh",
          "-c",
          "/usr/sbin/sshd \u0026\u0026 /bin/bash"
        ],
...

是不是dockerfile的 ENTRYPOINT /usr/sbin/sshd && /bin/bash 到Kubernetes中不能正常运行了?为何Dockerfile配置中 && 符号到了Kubernetes中成了 \u0026\u0026

对比

  • 尝试对比一个简单的httpd容器:

    kubectl run test --image=docker.io/centos/httpd
    
  • 这个标准镜像启动是正常的:

    kubectl get pods -o wide
    

显示:

NAME   READY   STATUS    RESTARTS   AGE   IP           NODE          NOMINATED NODE   READINESS GATES
test   1/1     Running   0          43m   10.244.4.2   dev-worker5   <none>           <none>