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Kubernetes从Private Registry中拉取容器镜像的方法

话接上文,在《 使用go-ceph管理Ceph RBD映像
》一文中我们提到了,我们需要自建一个ceph rbd api service用于给我的产品控制台提供RESTful API服务接口。这个服务我也是打算放在kubernetes集群中作为一个Service运行的。这两天完成了这个服务开发,并编写完Service的Dockerfile,将镜像build, tag并push到了我们在阿里云的私有镜像库。但在通过kubectl创建这个Service时,我们遇到了 ErrImagePull、ImagePullBackOff等Pod status,通过kubectl describe pod/{MyPod}命令查看,发现下面错误提示:

23s    5s    2    {kubelet 10.57.136.60}    spec.containers{rbd-rest-api}    Warning    Failed        Failed to pull image "registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api:latest": image pull failed for registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api:latest, this may be because there are no credentials on this request.  details: (Error: image xxxx/rbd-rest-api:latest not found)

面前这个坑就是Kubernetes集群如何从Private Registry获取容器镜像的问题。关于这个问题, K8s官方文档
有较为 详细的说明
,但填过坑的人都知道,那些说明还是远远不够的,实践中你会碰到很多意想不到的问题。这里就来结合实际操作说说K8s与私有容器镜像仓库是如何在一起欢乐的工作的^_^。

一、环境

由于 Kubernetes
和Docker都在Active Develop的过程中,两个项目的变动都很快,因此,特定的操作和说明在某些版本是好用的,但对另外一些版本却是不灵光的。这里先把环境确定清楚,避免误导。

OS:
Ubuntu 14.04.4 LTS Kernel:3.19.0-70-generic #78~14.04.1-Ubuntu SMP Fri Sep 23 17:39:18 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

Docker:
# docker version
Client:
 Version:      1.12.2
 API version:  1.24
 Go version:   go1.6.3
 Git commit:   bb80604
 Built:        Tue Oct 11 17:00:50 2016
 OS/Arch:      linux/amd64

Server:
 Version:      1.12.2
 API version:  1.24
 Go version:   go1.6.3
 Git commit:   bb80604
 Built:        Tue Oct 11 17:00:50 2016
 OS/Arch:      linux/amd64

Kubernetes集群:1.3.7

私有镜像仓库:阿里云镜像仓库

Docker镜像:非公共镜像,大家在测试中可以在自己的私有仓库建立自己的测试镜像
registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api:latest

Kubernets在文档中描述了几种访问私有仓库的方法,这里挑选了那些可操作的,逐一测试一下。

二、方法1:利用Node上的配置访问Private Registry

在玩Docker时,很多朋友都 搭建过自己的Private Registry
。Docker访问那些以basic auth方式进行鉴权的Private Registry,只需在本地执行docker login,输入用户名、密码后,就可以自由向Registry Push镜像或pull 镜像到本地了:

# docker login registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api
Username: {UserName}
Password:
Login Succeeded

在这一过程结束后,Docker实际上会在~/.docker目录下创建一个config.json文件,保存后续与Registry交互过程中所要使用的鉴权串(这个鉴权串只是一个base64编码结果,安全性欠佳^_^):

# cat ~/.docker/config.json
{
    "auths": {
        "registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api": {
            "auth": "xxxxyyyyzzzz"
        }
    }
}

一但Node上有了这个配置,那么K8s就可以通过docker直接访问Private Registry了,这是 K8s文档中与私有镜像仓库交互的第一个方法
。考虑到Pod可以被调度到集群中的任意一个Node上,需要在每个Node上执行上述login操作,或者可以简单地将~/.docker/config.json scp到各个node上的~/.docker目录下。

实际效果如何呢? 我们创建了一个Pod yaml,测试一下是否能run起来:

//rbd-rest-api-using-node-config.yaml
apiVersion: v1
kind: Pod
metadata:
  name: rbd-rest-api-using-node-config
spec:
  containers:
  - name: rbd-rest-api-using-node-config
    image: registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api:latest
    imagePullPolicy: Always

我们来创建一下这个Pod并查看pod的创建状态:

# kubectl create -f rbd-rest-api-using-node-config.yaml
pod "rbd-rest-api-using-node-config" created
# kubectl get pods
NAME                             READY     STATUS             RESTARTS   AGE
rbd-rest-api-using-node-config   0/1       ErrImagePull       0          5s

通过describe查看Pod失败的详细信息:

# kubectl describe pod/rbd-rest-api-using-node-config
... ...

Events:
  FirstSeen    LastSeen    Count    From            SubobjectPath                    Type        Reason        Message
  ---------    --------    -----    ----            -------------                    --------    ------        -------
  1m        1m        1    {default-scheduler }                            Normal        Scheduled    Successfully assigned rbd-rest-api-using-node-config to 10.66.181.146
  1m        42s        3    {kubelet 10.66.181.146}    spec.containers{rbd-rest-api-using-node-config}    Normal        Pulling        pulling image "registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api:latest"
  1m        42s        3    {kubelet 10.66.181.146}    spec.containers{rbd-rest-api-using-node-config}    Warning        Failed        Failed to pull image "registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api:latest": image pull failed for registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api:latest, this may be because there are no credentials on this request.  details: (Error: image xxxx/rbd-rest-api:latest not found)
  1m        42s        3    {kubelet 10.66.181.146}                            Warning        FailedSync    Error syncing pod, skipping: failed to "StartContainer" for "rbd-rest-api-using-node-config" with ErrImagePull: "image pull failed for registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api:latest, this may be because there are no credentials on this request.  details: (Error: image xxxx/rbd-rest-api:latest not found)"
... ...

这个方法对我们的环境并不有效。并且经过多次测试,结果依旧,K8s无法从Private Registry获取我们想要的镜像文件:(。

三、方法2:通过kubectl创建docker-registry的secret

K8s提供的第二种方法是通过kubectl创建一个 docker-registry的secret,并在Pod描述文件中引用该secret以达到从Private Registry Pull Image的目的。

操作之前,我们先删除掉各个Node上的~/.docker/config.json。

执行kubectl create secret docker-registry时需要提供private registry的访问UserName和Password:

# kubectl create secret docker-registry registrykey-m2-1 --docker-server=registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api --docker-username={UserName} --docker-password={Password} --docker-email=team@domain.com
secret "registrykey-m2-1" created

# kubectl get secret
NAME                  TYPE                                  DATA      AGE
registrykey-m2-1      kubernetes.io/dockercfg               1         29s

secret: registrykey-m2-1创建成功。我们来测试一下引用这个secret对象的Pod是否能Pull Image成功并Run起来。Pod yaml文件如下:

//rbd-rest-api-registrykey-m2-1.yaml

apiVersion: v1
kind: Pod
metadata:
  name: rbd-rest-api-registrykey-m2-1
spec:
  containers:
  - name: rbd-rest-api-registrykey-m2-1
    image: registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api:latest
    imagePullPolicy: Always
  imagePullSecrets:
  - name: registrykey-m2-1

创建Pod,并观察Pod状态:

# kubectl create -f rbd-rest-api-registrykey-m2-1.yaml
pod "rbd-rest-api-registrykey-m2-1" created

# kubectl get pods
NAME                             READY     STATUS             RESTARTS   AGE
rbd-rest-api-registrykey-m2-1    1/1       Running            0          7s
rbd-rest-api-using-node-config   0/1       ImagePullBackOff   0          29m

通过describe pod,查看创建的event序列:

Events:
  FirstSeen    LastSeen    Count    From            SubobjectPath                    Type        Reason        Message
  ---------    --------    -----    ----            -------------                    --------    ------        -------
  1m        1m        1    {default-scheduler }                            Normal        Scheduled    Successfully assigned rbd-rest-api-registrykey-m2-1 to 10.57.136.60
  1m        1m        1    {kubelet 10.57.136.60}    spec.containers{rbd-rest-api-registrykey-m2-1}    Normal        Pulling        pulling image "registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api:latest"
  1m        1m        1    {kubelet 10.57.136.60}    spec.containers{rbd-rest-api-registrykey-m2-1}    Normal        Pulled        Successfully pulled image "registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api:latest"
  1m        1m        1    {kubelet 10.57.136.60}    spec.containers{rbd-rest-api-registrykey-m2-1}    Normal        Created        Created container with docker id d842565e762d
  1m        1m        1    {kubelet 10.57.136.60}    spec.containers{rbd-rest-api-registrykey-m2-1}    Normal        Started        Started container with docker id d842565e762d

正如我们期望的那样,引用了secret: registrykey-m2-1的Pod成功Run起来了。

如果一个pod中有来自不同私有仓库的不同镜像,我们需要怎么做呢?通过kubectl create secret docker-registry我们一次只能建立一个registrykey,如果要访问两个镜像仓库,我们就需要分别为每个仓库创建一个registrykey。我们再来创建一个registrykey,对应的仓库为:registry.cn-hangzhou.aliyuncs.com/xxxx/test:

# kubectl create secret docker-registry registrykey-m2-2 --docker-server=registry.cn-hangzhou.aliyuncs.com/xxxx/test --docker-username={UserName} --docker-password={Password} --docker-email=team@domain.com
secret "registrykey-m2-2" created

root@node1:~/pullimagetest/test# kubectl get secret
NAME                  TYPE                                  DATA      AGE
registrykey-m2-1      kubernetes.io/dockercfg               1         1h
registrykey-m2-2      kubernetes.io/dockercfg               1         6s

接下来,我们来建一个包含多个container的Pod:

//rbd-rest-api-multi-registrykeys-m2-2.yaml

apiVersion: v1
kind: Pod
metadata:
  name: rbd-rest-api-multi-registrykeys-m2-2
spec:
  containers:
  - name: rbd-rest-api-multi-registrykeys-m2-2
    image: registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api:latest
    imagePullPolicy: Always
  - name: test-multi-registrykeys-m2-2
    image: registry.cn-hangzhou.aliyuncs.com/xxxx/test:latest
    imagePullPolicy: Always
    command:
       - "tail"
       - "-f"
       - "/var/log/bootstrap.log"
  imagePullSecrets:
  - name: registrykey-m2-1
  - name: registrykey-m2-2

在secret引用中,我们将两个key都引用了进来。

创建该Pod:

# kubectl create -f rbd-rest-api-multi-registrykeys-m2-2.yaml
pod "rbd-rest-api-multi-registrykeys-m2-2" created

# kubectl get pod
NAME                                   READY     STATUS             RESTARTS   AGE
rbd-rest-api-multi-registrykeys-m2-2   2/2       Running            0          5s

通过pod的event,我们看看启动的操作顺序:

Events:
  FirstSeen    LastSeen    Count    From            SubobjectPath                        Type        Reason        Message
  ---------    --------    -----    ----            -------------                        --------    ------        -------
  44s        44s        1    {default-scheduler }                                Normal        Scheduled    Successfully assigned rbd-rest-api-multi-registrykeys-m2-2 to 10.57.136.60
  43s        43s        1    {kubelet 10.57.136.60}    spec.containers{rbd-rest-api-multi-registrykeys-m2-2}    Normal        Pulling        pulling image "registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api:latest"
  43s        43s        1    {kubelet 10.57.136.60}    spec.containers{rbd-rest-api-multi-registrykeys-m2-2}    Normal        Pulled        Successfully pulled image "registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api:latest"
  42s        42s        1    {kubelet 10.57.136.60}    spec.containers{rbd-rest-api-multi-registrykeys-m2-2}    Normal        Created        Created container with docker id 7c09048a41f6
  42s        42s        1    {kubelet 10.57.136.60}    spec.containers{rbd-rest-api-multi-registrykeys-m2-2}    Normal        Started        Started container with docker id 7c09048a41f6
  42s        42s        1    {kubelet 10.57.136.60}    spec.containers{test-multi-registrykeys-m2-2}        Normal        Pulling        pulling image "registry.cn-hangzhou.aliyuncs.com/xxxx/test:latest"
  42s        42s        1    {kubelet 10.57.136.60}    spec.containers{test-multi-registrykeys-m2-2}        Normal        Pulled        Successfully pulled image "registry.cn-hangzhou.aliyuncs.com/xxxx/test:latest"
  42s        42s        1    {kubelet 10.57.136.60}    spec.containers{test-multi-registrykeys-m2-2}        Normal        Created        Created container with docker id 9930834fe4a3
  42s        42s        1    {kubelet 10.57.136.60}    spec.containers{test-multi-registrykeys-m2-2}        Normal        Started        Started container with docker id 9930834fe4a3

k8s分别从两个镜像仓库尝试pull image,并且最终都成功了!

四、方法3:通过secret yaml文件创建pull image所用的secret

除了上面通过kubectl可以快捷的创建pull image所用的secret外,我们还可以使用常规的手段-yaml描述文件来创建我们需要的secret资源。

//registrykey-m3-1.yaml
apiVersion: v1
kind: Secret
metadata:
  name: registrykey-m3-1
  namespace: default
data:
    .dockerconfigjson: {base64 -w 0 ~/.docker/config.json}
type: kubernetes.io/dockerconfigjson

前面说过docker login会在~/.docker下面创建一个config.json文件保存鉴权串,这里secret yaml的.dockerconfigjson后面的数据就是那个json文件的base64编码输出(-w 0让base64输出在单行上,避免折行)。

创建registrykey-m3-1 secret:

# kubectl create -f registrykey-m3-1.yaml
secret "registrykey-m3-1" created

# kubectl get secret
NAME                  TYPE                                  DATA      AGE
myregistrykey3        kubernetes.io/dockerconfigjson        1         3h
registrykey-m2-1      kubernetes.io/dockercfg               1         1h
registrykey-m2-2      kubernetes.io/dockercfg               1         23m
registrykey-m3-1      kubernetes.io/dockerconfigjson        1         29s

对比后,我们发现通过kubectl和yaml创建的两个registrykey secret的类型略有不同,前者是kubernetes.io/dockercfg,后者是kubernetes.io/dockerconfigjson。

接下来,我们编写一个引用了registrykey-m3-1的Pod:

//rbd-rest-api-registrykey-m3-1.yaml
apiVersion: v1
kind: Pod
metadata:
  name: rbd-rest-api-registrykey-m3-1
spec:
  containers:
  - name: rbd-rest-api-registrykey-m3-1
    image: registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api:latest
    imagePullPolicy: Always
  imagePullSecrets:
  - name: registrykey-m3-1

创建Pod:

# kubectl create -f rbd-rest-api-registrykey-m3-1.yaml
pod "rbd-rest-api-registrykey-m3-1" created
# kubectl get pods
NAME                            READY     STATUS             RESTARTS   AGE
rbd-rest-api-registrykey-m3-1   1/1       Running            0          8s

创建成功。

那么这种方法如何应对含有来自多个镜像仓库container的Pod的呢?这里的思路与方法2略有不同。我们不需要创建并引用两个或多个secret,而是创建一个可以访问多个私有镜像仓库的secret,我们需要将多个镜像仓库的访问鉴权串都放到~/.docker/config.json中:

按照方法1的介绍,我们先login registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api,得到config.json如下:

{
    "auths": {
        "registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api": {
            "auth": "....省略...."
        }
    }
}

我们再login registry.cn-hangzhou.aliyuncs.com/xxxx/test,得到config.json如下:

{
    "auths": {
        "registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api": {
            "auth": "....省略...."
        },
        "registry.cn-hangzhou.aliyuncs.com/xxxx/test": {
            "auth": "....省略...."
        }
    }
}

我们看到Docker自动将新login的private registry的鉴权串merge到了同一个config.json中了。现在我们基于该包含了两个库鉴权串的config.json创建一个新secret:registrykey-m3-2:

//registrykey-m3-2.yaml

apiVersion: v1
kind: Secret
metadata:
  name: registrykey-m3-2
  namespace: default
data:
  .dockerconfigjson: {base64 -w 0 ~/.docker/config.json}
type: kubernetes.io/dockerconfigjson

创建secret: registrykey-m3-2

# kubectl create -f registrykey-m3-2.yaml
secret "registrykey-m3-2" created

# kubectl get secrets
NAME                  TYPE                                  DATA      AGE
registrykey-m2-1      kubernetes.io/dockercfg               1         1h
registrykey-m2-2      kubernetes.io/dockercfg               1         42m
registrykey-m3-1      kubernetes.io/dockerconfigjson        1         19m
registrykey-m3-2      kubernetes.io/dockerconfigjson        1         6s

我们编辑一个包含两个容器,引用secret “registrykey-m3-2″ 的Pod yaml:

//rbd-rest-api-multi-registrykeys-m3-2.yaml

apiVersion: v1
kind: Pod
metadata:
  name: rbd-rest-api-multi-registrykeys-m3-2
spec:
  containers:
  - name: rbd-rest-api-multi-registrykeys-m3-2
    image: registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api:latest
    imagePullPolicy: Always
  - name: test-multi-registrykeys-m3-2
    image: registry.cn-hangzhou.aliyuncs.com/xxxx/test:latest
    imagePullPolicy: Always
    command:
       - "tail"
       - "-f"
       - "/var/log/bootstrap.log"
  imagePullSecrets:
  - name: registrykey-m3-2

创建该Pod:

# kubectl create -f rbd-rest-api-multi-registrykeys-m3-2.yaml
pod "rbd-rest-api-multi-registrykeys-m3-2" created

# kubectl get pod
NAME                                   READY     STATUS             RESTARTS   AGE
rbd-rest-api-multi-registrykeys-m3-2   2/2       Running            0          4s

Pod创建成功!

五、调用API创建registrykey secret

对比了方法2和方法3,方法2更简洁,方法3更强大。但在任何一个产品中,secret都不应该是手动创建的,在这种情况下, API
创建 registrykey secret
便是必经之路。一旦选择通过API创建,我们显然将依仗着方法2中的原理,将config.json中的内容通过API请求的Body Post给K8s api server。

如何在远端构建出config.json的内容呢继而构建出secret yaml中.dockerconfigjson的值数据呢?我们发现config.json套路中,唯一不确定的就是每个private repository下的auth串,那么这个串是啥呢?你大可base64 -d一下:

# echo -n "VXNlck5hbWU6UGFzc3dvcmQ="|base64 -d
UserName:Password

没错,实质上这个auth串就是UserName:Password的base64编码值。因此,你首先要用某个仓库的UserName和Password按照’UserName:Password’格式进行base64编码,利用编码的结果值构造json内容,比如:

{
    "auths": {
        "registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api": {
            "auth": "VXNlck5hbWU6UGFzc3dvcmQ="
        }
}

然后对这段json数据再做base64编码,所得到的值就是secret yaml中的.dockerconfigjson的值数据。至此,我们来通过API创建一个secret:

$ curl -v -H "Content-type: application/json"  -X POST -d ' {
  "apiVersion": "v1",
  "kind": "Secret",
  "metadata": {
    "name": "registrykey-m4-1",
    "namespace": "default"
  },
  "data": {
    ".dockerconfigjson": "{cat ~/.docker/config.json |base64 -w 0}"
  },
  "type": "kubernetes.io/dockerconfigjson"
}' http://10.57.136.60:8080/api/v1/namespaces/default/secrets

# kubectl get secret
NAME                  TYPE                                  DATA      AGE
registrykey-m2-1      kubernetes.io/dockercfg               1         2h
registrykey-m2-2      kubernetes.io/dockercfg               1         1h
registrykey-m3-1      kubernetes.io/dockerconfigjson        1         43m
registrykey-m3-2      kubernetes.io/dockerconfigjson        1         24m
registrykey-m4-1      kubernetes.io/dockerconfigjson        1         18s

基于registrykey-m4-1,我们启动一个Pod:

//rbd-rest-api-registrykey-m4-1.yaml

apiVersion: v1
kind: Pod
metadata:
  name: rbd-rest-api-registrykey-m4-1
spec:
  containers:
  - name: rbd-rest-api-registrykey-m4-1
    image: registry.cn-hangzhou.aliyuncs.com/xxxx/rbd-rest-api:latest
    imagePullPolicy: Always
  imagePullSecrets:
  - name: registrykey-m4-1

# kubectl create -f rbd-rest-api-registrykey-m4-1.yaml
pod "rbd-rest-api-registrykey-m4-1" created

# kubectl get pod
NAME                            READY     STATUS             RESTARTS   AGE
rbd-rest-api-registrykey-m4-1   1/1       Running            0          5s

Pod创建成功!

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