openshift 使用curl命令访问apiserver

openshift版本：openshift v3.6.173.0.5

使用oc(同kubectl)命令访问apiserver资源的时候，会使用到/root/.kube/config文件中使用的配置。

使用user访问apiserver

oc命令使用config中定义的user和证书(公钥和私钥)访问apiserver。使用如下命令查看当前使用的config上下文：monitor为当前的namespace，test-openshfit-com:8443为apiserver暴露的server，system:admin为访问apiserver使用的user名称

# oc config current-context
monitor/test-openshfit-com:/system:admin

查看system:admin对应的证书(下面使用变量代替)

users:
- name: system:admin/test-openshift-com:
  user:
    client-certificate-data: ${CA}
    client-key-data: ${KEY}

导出证书，将下面decode出的内容分别保存到/home/ca.cert，/home/ca.key

# echo -n ${CA}|base64 --decode   #/home/ca.cert
# echo -n ${KEY}|base64 --decode  #/home/ca.key

使用如下方式即可访问cluster范围内的资源，该方式与oc命令的原理一样。下面以访问servers为例

APISERVER=$(kubectl config view --minify -o jsonpath='{.clusters[0].cluster.server}')
curl $APISERVER/api/v1/services --cert /home/ca.cert --key /home/ca.key --user system:admin

使用serviceaccount访问apiserver

serviceaccount除了可以为pod提供secret外，还可以作为访问apiserver资源的凭证。使用如下命令创建一个名为curltest的serviceaccount，并获取其token

oc create serviceaccount curltest
APISERVER=$(kubectl config view --minify -o jsonpath='{.clusters[0].cluster.server}')
TOKEN=$(oc serviceaccounts get-token curltest)

使用如下命令进行rolebinding之后就可以查看namespaces为monitor下面的资源，但不可以查看其他namespace的资源。system:master可以看作一个超级账户，可参见user-facing-roles

oc policy add-role-to-user system:master -z curltest
curl $APISERVER/api/v1/namespaces/monitor/services --header "Authorization: Bearer $TOKEN"

使用下面命令查看当前rolebinding情况，可以查看当前serveraccount可进行的操作权限。注：openshift的add-role-to-user/add-cluster-role-to-user其实就是kubernetes进行rolebinding/clusterrolebinding的操作，将一个role权限赋予一个user或serviceaccount。

# oc describe rolebinding system:master
Name:                   system:master
Namespace:              monitor
Created:                 minutes ago
Labels:                 <none>
Annotations:            <none>
Role:                   /system:master
Users:                  <none>
Groups:                 <none>
ServiceAccounts:        curltest
Subjects:               <none>
Verbs                   Non-Resource URLs       Resource Names  API Groups      Resources
[*]                     []                      []              [*]             [*]
[*]                     [*]                     []              []              []

使用如下命令进行clusterrolebinding之后就可以访问cluster范围内的资源，首先需要删除先前的rolebinding

oc policy remove-role-from-user system:master -z curltest
oadm policy add-cluster-role-to-user system:master -z curltest
TOKEN=$(oc serviceaccounts get-token curltest)
curl $APISERVER/api/v1/services --header "Authorization: Bearer $TOKEN"

查看clusterrolebinding情况

# oc describe clusterrolebinding system:master
Name:                   system:masters
Created:                 weeks ago
Labels:                 <none>
Annotations:            <none>
Role:                   /system:master
Users:                  <none>
Groups:                 system:masters
ServiceAccounts:        monitor/curltest
Subjects:               <none>
Verbs                   Non-Resource URLs       Resource Names  API Groups      Resources
[*]                     []                      []              [*]             [*]
[*]                     [*]                     []              []              []

环境清理

oadm policy remove-cluster-role-from-user system:master -z liu
oc delete sa curltest

下面演示pod如何使用serviceaccount访问apiserver资源，参照在Kubernetes Pod中使用Service Account访问API Server

首先安装minikube和go，方法可以参见https://www.cnblogs.com/charlieroro/p/10434138.html。minikube启动时直接使用docker驱动即可：minikube start --vm-driver=none

对client-go的操作步骤用于生成测试镜像，可以直接下载已经打包好的镜像(docker pull docker push woodliu268/k8s-example)来跳过下面相关操作

安装client-go，client使用了go module方式来管理包依赖(client-go根目录下使用go.mod和go.sum来管理包)，参见Installing client-go

export GO111MODULE=on
go mod init
go get k8s.io/client-go@master

修改client-go/examples/in-cluster-client-configuration/main.go目录下，将panic全部修改为fmt.Println，执行如下命令编译为可执行程序main

go build -o main main.go

Dockerfile内容如下，编译为docker镜像

FROM debian
COPY main /root/main
RUN chmod +x /root/main
WORKDIR /root
ENTRYPOINT ["/root/main"]

docker build -t k8s/example1:latest .

使用如下deployment创建pod，默认创建的default命名空间

# cat deployment.yaml
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: k8s-example
spec:
  replicas:
  template:
    metadata:
      labels:
        run: k8s-example
    spec:
      containers:
      - name: k8s-example
        image: k8s/example1:latest
        imagePullPolicy: IfNotPresent

kubectl log -f k8s-example-7747697dbf-772df时发现有如下错误。说明pod使用用户system:serviceaccount:default:default访问apiserver的时候访问失败

pods is forbidden: User "system:serviceaccount:default:default" cannot list resource "pods" in API group "" at the cluster scope
There are  pods in the cluster

由于需要在cluster范围内访问pod资源，下面创建clusterrole和clusterrolebinding(参考Using RBAC Authorization)，并赋予system:serviceaccount:default:default list pod的权限

# cat clusterrole.yaml
kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  namespace: default
  name: pod-reader
rules:
- apiGroups: [""]
  resources: ["pods"]
  verbs: ["get", "watch", "list"]
# cat clusterrolebinding.yaml
kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: read-pods
  namespace: default
subjects:
- kind: User
  name: system:serviceaccount:default:default
  apiGroup: rbac.authorization.k8s.io
roleRef:
  kind: ClusterRole
  name: pod-reader
  apiGroup: rbac.authorization.k8s.io

重新创建deployment，查看pod日志，可以正常读取cluster的pod信息

There are  pods in the cluster

PS：

• 使用kubectl get RESOURECE -v=NUM可以查看kubectl的与apiserver的交互，RESOURECE为pod，service等；NUM取值为6-8
• 使用oc config use-context可以设置kubeconfig文件中的current-context字段
• Service account 验证时用户名 system:serviceaccount:(NAMESPACE):(SERVICEACCOUNT)，被指定到组 system:serviceaccounts 和 system:serviceaccounts:(NAMESPACE)
• 应用程序可能会在如yaml模板中使用serviceaccount挂载到pod中的tls证书来访问apiserver资源

参考：

https://kubernetes.io/docs/reference/access-authn-authz/rbac/

https://docs.openshift.com/container-platform/3.5/rest_api/index.html

https://docs.openshift.com/container-platform/3.9/admin_guide/manage_rbac.html

https://docs.openshift.com/enterprise/3.0/admin_guide/manage_authorization_policy.html

https://jimmysong.io/posts/user-authentication-in-kubernetes/