三种监控 Kubernetes 集群证书过期方案

###   
前言

Kubernetes 中大量用到了证书, 比如 ca证书、以及 kubelet、apiserver、proxy、etcd等组件，还有 kubeconfig 文件。

如果证书过期，轻则无法登录 Kubernetes 集群，重则整个集群异常。

为了解决证书过期的问题，一般有以下几种方式：

1.大幅延长证书有效期，短则 10年，长则 100 年；2.证书快过期是自动轮换，如 Rancher 的 K3s，RKE2 就采用这种方式；3.增加证书过期的监控，便于提早发现证书过期问题并人工介入

本次主要介绍关于 Kubernetes 集群证书过期的监控，这里提供 3 种监控方案：

1.使用 Blackbox Exporter\[1\] 通过 Probe 监控 Kubernetes apiserver 证书过期时间；2.使用 kube-prometheus-stack\[2\] 通过 apiserver 和 kubelet 组件监控获取相关证书过期时间;3.使用 enix 的 x509-certificate-exporter\[3\]监控集群所有node的 `/etc/kubernetes/pki` 和 `/var/lib/kubelet` 下的证书以及 kubeconfig 文件

### 方案一: Blackbox Exporter 监控 Kubernetes apiserver 证书过期时间

Blackbox Exporter 用于探测 HTTPS、HTTP、TCP、DNS、ICMP 和 grpc 等 Endpoint。在你定义 Endpoint 后，Blackbox Exporter 会生成指标，可以使用 Grafana 等工具进行可视化。Blackbox Exporter 最重要的功能之一是测量 Endpoint 的可用性。

当然, Blackbox Exporter 探测 HTTPS 后就可以获取到证书的相关信息, 就是利用这种方式实现对 Kubernetes apiserver 证书过期时间的监控.

#### 配置步骤

1.调整 Blackbox Exporter 的配置, 增加 `insecure_tls_verify: true`, 如下:

![87630800bdd821d9c253cc4cdf32c8a8.jpeg](/media/202411/2024-11-02_190717_0136180.10570746321801738.jpeg)

调整 Blackbox Exporter 配置

2.重启 blackbox exporter: `kubectl rollout restart deploy ...`3.增加对 Kubernetes APIServer 内部端点https://kubernetes.default.svc.cluster.local/readyz的监控.1.如果你没有使用 Prometheus Operator, 使用的是原生的 Prometheus, 则需要修改 Prometheus 配置文件的 configmap 或 secret, 添加 scrape config, 示例如下:

![71ed475ca567c6d238e32d56ef3e494a.png](/media/202411/2024-11-02_190718_3848570.7016353780321659.png)

Prometheus 增加 scrape config

2.如果在使用 Prometheus Operator, 则可以增加如下 Probe CRD, Prometheus Operator 会自动将其转换并 merge 到 Prometheus 中.

```yaml
apiVersion: monitoring.coreos.com/v1
kind: Probe
metadata:
  name: kubernetes-apiserver
spec:
  interval: 60s
  module: http_2xx
  prober:
    path: /probe
    url: monitor-prometheus-blackbox-exporter.default.svc.cluster.local:9115
  targets:
    staticConfig:
      static:
      - https://kubernetes.default.svc.cluster.local/readyz
```

最后, 可以增加 Prometheus 告警 Rule, 这里就直接用 Prometheus Operator 创建 PrometheusRule CRD 做示例了, 示例如下:

```yaml
apiVersion: monitoring.coreos.com/v1
kind: PrometheusRule
metadata:
  name: prometheus-blackbox-exporter
spec:
  groups:
  - name: prometheus-blackbox-exporter
    rules:
    - alert: BlackboxSslCertificateWillExpireSoon
      expr: probe_ssl_earliest_cert_expiry - time() < 86400 * 30
      for: 0m
      labels:
        severity: warning
    - alert: BlackboxSslCertificateWillExpireSoon
      expr: probe_ssl_earliest_cert_expiry - time() < 86400 * 14
      for: 0m
      labels:
        severity: critical
    - alert: BlackboxSslCertificateExpired
      annotations:
        description: |-
          SSL certificate has expired already
            VALUE = {{ $value }}
            LABELS = {{ $labels }}
        summary: SSL certificate expired (instance {{ $labels.instance }})
      expr: probe_ssl_earliest_cert_expiry - time() <= 0
      for: 0m
      labels:
        severity: emergency
```

#### 效果

![ce109637f748faab9c8b24daf4b6fe24.png](/media/202411/2024-11-02_190717_5712380.4925743326266514.png)

Probe 查询证书过期时间

### 方案二: kube-prometheus-stack 通过 apiserver 和 kubelet 组件监控证书过期时间

这里可以参考我的文章:Prometheus Operator 与 kube-prometheus 之二 - 如何监控 1.23+ kubeadm 集群\[4\], 安装完成后, 开箱即用.

开箱即用内容包括:

1.抓取 apiserver 和 kubelet 指标;(即 serviceMonitor)2.配置证书过期时间的相关告警; (即 PrometheusRule)

这里用到的指标有:

1.apiserver1.`apiserver_client_certificate_expiration_seconds_count`2.`apiserver_client_certificate_expiration_seconds_bucket`2.kubelet1.`kubelet_certificate_manager_client_expiration_renew_errors`2.`kubelet_server_expiration_renew_errors`3.`kubelet_certificate_manager_client_ttl_seconds`4.`kubelet_certificate_manager_server_ttl_seconds`

#### 监控效果

对应的 Prometheus 告警规则如下:

![4b07f19f378c4522a702bf79fd168efa.png](/media/202411/2024-11-02_190720_2127160.7305774469221233.png)

证书过期时间相关 PrometheusRule

### 方案三: 使用 enix 的 x509-certificate-exporter

#### 监控手段

该 Exporter 是通过监控集群所有node的指定目录或 path 下的证书文件以及 kubeconfig 文件来获取证书信息.

如果是使用 kubeadm 搭建的 Kubernetes 集群, 则可以监控如下包含证书的文件和 kubeconfig:

```yaml
watchFiles:
- /var/lib/kubelet/pki/kubelet-client-current.pem
- /etc/kubernetes/pki/apiserver.crt
- /etc/kubernetes/pki/apiserver-etcd-client.crt
- /etc/kubernetes/pki/apiserver-kubelet-client.crt
- /etc/kubernetes/pki/ca.crt
- /etc/kubernetes/pki/front-proxy-ca.crt
- /etc/kubernetes/pki/front-proxy-client.crt
- /etc/kubernetes/pki/etcd/ca.crt
- /etc/kubernetes/pki/etcd/healthcheck-client.crt
- /etc/kubernetes/pki/etcd/peer.crt
- /etc/kubernetes/pki/etcd/server.crt
watchKubeconfFiles:
- /etc/kubernetes/admin.conf
- /etc/kubernetes/controller-manager.conf
- /etc/kubernetes/scheduler.conf
```

#### 安装配置

编辑 values.yaml:

```yaml
kubeVersion: ''
extraLabels: {}
nameOverride: ''
fullnameOverride: ''
imagePullSecrets: []
image:
  registry: docker.io
  repository: enix/x509-certificate-exporter
  tag:
  pullPolicy: IfNotPresent
psp:
  create: false
rbac:
  create: true
  secretsExporter:
    serviceAccountName:
    serviceAccountAnnotations: {}
    clusterRoleAnnotations: {}
    clusterRoleBindingAnnotations: {}
  hostPathsExporter:
    serviceAccountName:
    serviceAccountAnnotations: {}
    clusterRoleAnnotations: {}
    clusterRoleBindingAnnotations: {}
podExtraLabels: {}
podAnnotations: {}
exposePerCertificateErrorMetrics: false
exposeRelativeMetrics: false
metricLabelsFilterList: null
secretsExporter:
  enabled: true
  debugMode: false
  replicas: 1
  restartPolicy: Always
  strategy: {}
  resources:
    limits:
      cpu: 200m
      memory: 150Mi
    requests:
      cpu: 20m
      memory: 20Mi
  nodeSelector: {}
  tolerations: []
  affinity: {}
  podExtraLabels: {}
  podAnnotations: {}
  podSecurityContext: {}
  securityContext:
    runAsUser: 65534
    runAsGroup: 65534
    readOnlyRootFilesystem: true
    capabilities:
      drop:
        - ALL
  secretTypes:
    - type: kubernetes.io/tls
      key: tls.crt
  includeNamespaces: []
  excludeNamespaces: []
  includeLabels: []
  excludeLabels: []
  cache:
    enabled: true
    maxDuration: 300
hostPathsExporter:
  debugMode: false
  restartPolicy: Always
  updateStrategy: {}
  resources:
    limits:
      cpu: 100m
      memory: 40Mi
    requests:
      cpu: 10m
      memory: 20Mi
  nodeSelector: {}
  tolerations: []
  affinity: {}
  podExtraLabels: {}
  podAnnotations: {}
  podSecurityContext: {}
  securityContext:
    runAsUser: 0
    runAsGroup: 0
    readOnlyRootFilesystem: true
    capabilities:
      drop:
        - ALL
  watchDirectories: []
  watchFiles: []
  watchKubeconfFiles: []
  daemonSets:
    cp:
      nodeSelector:
        node-role.kubernetes.io/master: ''
      tolerations:
        - effect: NoSchedule
          key: node-role.kubernetes.io/master
          operator: Exists
      watchFiles:
        - /var/lib/kubelet/pki/kubelet-client-current.pem
        - /etc/kubernetes/pki/apiserver.crt
        - /etc/kubernetes/pki/apiserver-etcd-client.crt
        - /etc/kubernetes/pki/apiserver-kubelet-client.crt
        - /etc/kubernetes/pki/ca.crt
        - /etc/kubernetes/pki/front-proxy-ca.crt
        - /etc/kubernetes/pki/front-proxy-client.crt
        - /etc/kubernetes/pki/etcd/ca.crt
        - /etc/kubernetes/pki/etcd/healthcheck-client.crt
        - /etc/kubernetes/pki/etcd/peer.crt
        - /etc/kubernetes/pki/etcd/server.crt
      watchKubeconfFiles:
        - /etc/kubernetes/admin.conf
        - /etc/kubernetes/controller-manager.conf
        - /etc/kubernetes/scheduler.conf
    nodes:
      watchFiles:
        - /var/lib/kubelet/pki/kubelet-client-current.pem
        - /etc/kubernetes/pki/ca.crt
rbacProxy:
  enabled: false
podListenPort: 9793
hostNetwork: false
service:
  create: true
  port: 9793
  annotations: {}
  extraLabels: {}
prometheusServiceMonitor:
  create: true
  scrapeInterval: 60s
  scrapeTimeout: 30s
  extraLabels: {}
  relabelings: {}
prometheusPodMonitor:
  create: false
prometheusRules:
  create: true
  alertOnReadErrors: true
  readErrorsSeverity: warning
  alertOnCertificateErrors: true
  certificateErrorsSeverity: warning
  certificateRenewalsSeverity: warning
  certificateExpirationsSeverity: critical
  warningDaysLeft: 30
  criticalDaysLeft: 14
  extraLabels: {}
  alertExtraLabels: {}
  rulePrefix: ''
  disableBuiltinAlertGroup: false
  extraAlertGroups: []
extraDeploy: []
```

通过 Helm Chart 安装:

```bash
helm repo add enix https://charts.enix.io
helm install x509-certificate-exporter enix/x509-certificate-exporter
```

通过这个 Helm Chart 也会自动安装:

•ServiceMonitor•PrometheusRule

其监控指标为:

•`x509_cert_not_after`

#### 监控效果

该 Exporter 还提供了一个比较花哨的 Grafana Dashboard, 如下:

![c346cd138424b6e6303982663c0b8f08.jpeg](/media/202411/2024-11-02_190717_5851320.09722338796465002.jpeg)

x509 Exporter Grafana Dashboard

Alert Rules 如下:

![ab666d0b83a2d33bb1226cab0ba676b3.png](/media/202411/2024-11-02_190717_4979500.38787064339576294.png)

x509 Exporter Prometheus Rule

### 总结

为了监控 Kubernetes 集群的证书过期时间, 我们提供了 3 种方案, 各有优劣:

1.使用 Blackbox Exporter\[5\] 通过 Probe 监控 Kubernetes apiserver 证书过期时间；1.优势: 实现简单;2.劣势: 只能监控 https 的证书;2.使用 kube-prometheus-stack\[6\] 通过 apiserver 和 kubelet 组件监控获取相关证书过期时间;1.优势: 开箱即用, 安装 kube-prometheus-stack 后无需额外安装其他 exporter2.劣势: 只能监控 apiserver 和 kubelet 的证书;3.使用 enix 的 x509-certificate-exporter\[7\]监控集群所有node的 `/etc/kubernetes/pki` 和 `/var/lib/kubelet` 下的证书以及 kubeconfig 文件1.优势: 可以监控所有 node, 所有 kubeconfig 文件, 以及 所有 tls 格式的 secret 证书, 如果要监控 Kubernetes 集群以外的证书, 也可以如法炮制; 范围广而全;2.需要额外安装: x509-certificate-exporter, 对应有 1 个 Deployment 和 多个 DaemonSet, 对 Kubernetes 集群的资源消耗不少.

可以根据您的实际情况灵活进行选择.

🎉🎉🎉

#### References

`[1]` Blackbox Exporter: _https://ewhisper.cn/posts/26225/_  
`[2]` kube-prometheus-stack: _https://ewhisper.cn/posts/3988/_  
`[3]` enix 的 x509-certificate-exporter: _https://github.com/enix/x509-certificate-exporter/_  
`[4]` Prometheus Operator 与 kube-prometheus 之二 - 如何监控 1.23+ kubeadm 集群: _https://ewhisper.cn/posts/3988/_  
`[5]` Blackbox Exporter: _https://ewhisper.cn/posts/26225/_  
`[6]` kube-prometheus-stack: _https://ewhisper.cn/posts/3988/_  
`[7]` enix 的 x509-certificate-exporter: _https://github.com/enix/x509-certificate-exporter/_