使用serviceaccount制作kubeconfig文件

背景

有时为了需要，我们需要给出一些具有特定集群权限的kubeconfig文件，这时我们可以通过使用serviceAccount来制作具有一定集群权限的kubeconfig

下面我们来使用这一技术创建一个只有greenstock命名空间权限的pod读取权限的kubeconfig

 

代码来源：https://gist.github.com/innovia/fbba8259042f71db98ea8d4ad19bd708

准备

1. 机器需要安装 jq

2. serviceAccount需要配置好rbac

• rbac的资料：https://jimmysong.io/kubernetes-handbook/guide/rbac.html
• service account: 
  • https://jimmysong.io/kubernetes-handbook/concepts/serviceaccount.html
  • https://jimmysong.io/kubernetes-handbook/guide/configure-pod-service-account.html

创建步骤

1. 创建好rbac.yaml

apiVersion: v1
kind: ServiceAccount
metadata:
  namespace: greenstock
  name: k8s-tester-sa
---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  namespace: greenstock
  name: greenstock-pod-reader
rules:
  - apiGroups: [""]
    resources: ["pods"]
    verbs: ["get", "watch", "list"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: k8s-tester-sa-rolebinding
  namespace: k8s-tester
subjects:
  - kind: ServiceAccount
    name: k8s-tester-sa
    namespace: greenstock
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: greenstock-pod-reader

 安装上述的文件 kubectl apply -f rbac.yaml

2.根据serviceaccount 生成kubeconfig

执行https://gist.github.com/innovia/fbba8259042f71db98ea8d4ad19bd708 这个里面的脚本，脚本内容如下 ：

#!/bin/bash
set -e
set -o pipefail

# Add user to k8s using service account, no RBAC (must create RBAC after this script)
if [[ -z "$1" ]] || [[ -z "$2" ]]; then
 echo "usage: $0  "
 exit 1
fi

SERVICE_ACCOUNT_NAME=$1
NAMESPACE="$2"
KUBECFG_FILE_NAME="/tmp/kube/k8s-${SERVICE_ACCOUNT_NAME}-${NAMESPACE}-conf"
TARGET_FOLDER="/tmp/kube"

create_target_folder() {
    echo -n "Creating target directory to hold files in ${TARGET_FOLDER}..."
    mkdir -p "${TARGET_FOLDER}"
    printf "done"
}

create_service_account() {
    echo -e "\\nCreating a service account in ${NAMESPACE} namespace: ${SERVICE_ACCOUNT_NAME}"
    kubectl create sa "${SERVICE_ACCOUNT_NAME}" --namespace "${NAMESPACE}"
}

get_secret_name_from_service_account() {
    echo -e "\\nGetting secret of service account ${SERVICE_ACCOUNT_NAME} on ${NAMESPACE}"
    SECRET_NAME=$(kubectl get sa "${SERVICE_ACCOUNT_NAME}" --namespace="${NAMESPACE}" -o json | jq -r .secrets[].name)
    echo "Secret name: ${SECRET_NAME}"
}

extract_ca_crt_from_secret() {
    echo -e -n "\\nExtracting ca.crt from secret..."
    kubectl get secret --namespace "${NAMESPACE}" "${SECRET_NAME}" -o json | jq \
    -r '.data["ca.crt"]' | base64 -D > "${TARGET_FOLDER}/ca.crt"
    printf "done"
}

get_user_token_from_secret() {
    echo -e -n "\\nGetting user token from secret..."
    USER_TOKEN=$(kubectl get secret --namespace "${NAMESPACE}" "${SECRET_NAME}" -o json | jq -r '.data["token"]' | base64 -D)
    printf "done"
}

set_kube_config_values() {
    context=$(kubectl config current-context)
    echo -e "\\nSetting current context to: $context"

    CLUSTER_NAME=$(kubectl config get-contexts "$context" | awk '{print $3}' | tail -n 1)
    echo "Cluster name: ${CLUSTER_NAME}"

    ENDPOINT=$(kubectl config view \
    -o jsonpath="{.clusters[?(@.name == \"${CLUSTER_NAME}\")].cluster.server}")
    echo "Endpoint: ${ENDPOINT}"

    # Set up the config
    echo -e "\\nPreparing k8s-${SERVICE_ACCOUNT_NAME}-${NAMESPACE}-conf"
    echo -n "Setting a cluster entry in kubeconfig..."
    kubectl config set-cluster "${CLUSTER_NAME}" \
    --kubeconfig="${KUBECFG_FILE_NAME}" \
    --server="${ENDPOINT}" \
    --certificate-authority="${TARGET_FOLDER}/ca.crt" \
    --embed-certs=true

    echo -n "Setting token credentials entry in kubeconfig..."
    kubectl config set-credentials \
    "${SERVICE_ACCOUNT_NAME}-${NAMESPACE}-${CLUSTER_NAME}" \
    --kubeconfig="${KUBECFG_FILE_NAME}" \
    --token="${USER_TOKEN}"

    echo -n "Setting a context entry in kubeconfig..."
    kubectl config set-context \
    "${SERVICE_ACCOUNT_NAME}-${NAMESPACE}-${CLUSTER_NAME}" \
    --kubeconfig="${KUBECFG_FILE_NAME}" \
    --cluster="${CLUSTER_NAME}" \
    --user="${SERVICE_ACCOUNT_NAME}-${NAMESPACE}-${CLUSTER_NAME}" \
    --namespace="${NAMESPACE}"

    echo -n "Setting the current-context in the kubeconfig file..."
    kubectl config use-context "${SERVICE_ACCOUNT_NAME}-${NAMESPACE}-${CLUSTER_NAME}" \
    --kubeconfig="${KUBECFG_FILE_NAME}"
}

create_target_folder
# create_service_account
get_secret_name_from_service_account
extract_ca_crt_from_secret
get_user_token_from_secret
set_kube_config_values

echo -e "\\nAll done! Test with:"
echo "KUBECONFIG=${KUBECFG_FILE_NAME} kubectl get pods"
echo "you should not have any permissions by default - you have just created the authentication part"
echo "You will need to create RBAC permissions"
KUBECONFIG=${KUBECFG_FILE_NAME} kubectl get pods

保存脚本名称为makekubecf.sh，执行命令是sh makekubecf.sh k8s-tester-sa greenstock

如果执行的时候遇到makekubecf.sh: 3: set: Illegal option -o pipefail，原因和解决方案可以参考https://my.oschina.net/u/1260221/blog/817458，主要就是切换成bash

3. 执行测试

假设上面 生成的脚本kubeconfig文件为config，执行kubectl get pod -n greensock --kubeconfig=./config

4. 开发小技巧

有时候呢，我们通过client-go在开发的时候，也可以通过这种方式来生成一个临时，符合我们的场景的serviceaccount，使用kubeconfigpath的方式来让我们的应用可以从集群外访问到我们已经开启了rbac的集群，具体的例子，可以查看 kubernetes-tester 项目，在项目中，我使用了一个“BuildConfigFromFlags”的方法，传入了kubeconfig文件，然后让应用获取到了指定serviceaccount的身份，也就是上面 的greenstock命令空间下的k8s-tester-sa从而方便了我们调试。