22.2 k8s中ksm采集的使用的dns解析

本节重点介绍 :

k8s 会为service创建cordns解析
pod中dns的搜索域
模拟prometheus进行dns解析后访问数据

k8s对象资源指标 kube-stats-metrics项目

prometheus 采集kube-state-metrics通过下面的配置段，

yaml 复制代码

- job_name: kube-state-metrics
  honor_timestamps: true
  scrape_interval: 30s
  scrape_timeout: 10s
  metrics_path: /metrics
  scheme: http
  static_configs:
  - targets:
    - kube-state-metrics:8080

采集配置解读

target这里配置的是kube-state-metrics:8080。

yaml 复制代码

  - targets:
    - kube-state-metrics:8080

因为kube-state-metrics部署好之后有个service。它的配置如下。

yaml 复制代码

apiVersion: v1
kind: Service
metadata:
  labels:
    app.kubernetes.io/name: kube-state-metrics
    app.kubernetes.io/version: v1.9.7
  name: kube-state-metrics
  namespace: kube-system
spec:
  clusterIP: None
  ports:
  - name: http-metrics
    port: 8080
    targetPort: http-metrics
  - name: telemetry
    port: 8081
    targetPort: telemetry
  selector:
    app.kubernetes.io/name: kube-state-metrics

k8s 会为service创建cordns解析

解析域名为${service_name}.${namespace}.svc.cluster.local
其中 cluster.local代表集群的后缀
那么kube-state-metrics的域名为kube-state-metrics.kube-system.svc.cluster.local

pod中dns的配置

同时pod中的dns配置为search 3个域，我们可以exec进入prometheus容器中查看，如下面的实例所示。

shell 复制代码

search kube-system.svc.cluster.local svc.cluster.local cluster.local
nameserver 10.96.0.10
options ndots:5

所以在容器中可以ping一下 kube-state-metrics，可以看到解析的ip地址

shell 复制代码

/prometheus $ ping kube-state-metrics
PING kube-state-metrics (10.100.71.4): 56 data bytes
ping: permission denied (are you root?)
/prometheus $

所以采集kube-state-metrics的target配置成 kube-state-metrics:8080是可以的，当然也可以配置成 kube-state-metrics.kube-system.svc:8080 和 kube-state-metrics.kube-system.svc.cluster.local:8080。

下面演示了不同搜索域的结果

shell 复制代码

/prometheus $ cat /etc/resolv.conf 
search kube-system.svc.cluster.local svc.cluster.local cluster.local
nameserver 10.96.0.10
options ndots:5
/prometheus $ ping kube-state-metrics
PING kube-state-metrics (10.100.71.4): 56 data bytes
ping: permission denied (are you root?)
/prometheus $ ping kube-state-metrics.kube-system
PING kube-state-metrics.kube-system (10.100.71.4): 56 data bytes
ping: permission denied (are you root?)
/prometheus $ ping kube-state-metrics.kube-system.svc
PING kube-state-metrics.kube-system.svc (10.100.71.4): 56 data bytes
ping: permission denied (are you root?)
/prometheus $ ping kube-state-metrics.kube-system.svc.cluster.local
PING kube-state-metrics.kube-system.svc.cluster.local (10.100.71.4): 56 data bytes
ping: permission denied (are you root?)

在节点上模拟prometheus访问 ksm

prometheus通过访问coredns，解析kube-state-metrics的域名，拿到相关ip，在访问kube-state-metrics 指标。
我们可以在node上模拟这一过程
在master上拿到coredns service 的ip

shell 复制代码

kubectl get svc  -n kube-system |grep dns
  kube-dns             ClusterIP   10.96.0.10     <none>        53/UDP,53/TCP,9153/TCP   73d

在node上请求 coredns 解析 kube-stats-metrics 域名，以为node上的 /etc/resolv.conf配置配置相关的解析域，所以要写全域名FQDN

shell 复制代码

[root@k8s-master01 ~]#  dig  kube-state-metrics.kube-system.svc.cluster.local @10.96.0.10  

; <<>> DiG 9.11.4-P2-RedHat-9.11.4-26.P2.el7_9.5 <<>> kube-state-metrics.kube-system.svc.cluster.local @10.96.0.10
;; global options: +cmd
;; Got answer:
;; WARNING: .local is reserved for Multicast DNS
;; You are currently testing what happens when an mDNS query is leaked to DNS
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 26378
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;kube-state-metrics.kube-system.svc.cluster.local. IN A

;; ANSWER SECTION:
kube-state-metrics.kube-system.svc.cluster.local. 30 IN A 10.100.85.200

;; Query time: 0 msec
;; SERVER: 10.96.0.10#53(10.96.0.10)
;; WHEN: Tue Aug 24 16:38:18 CST 2021
;; MSG SIZE  rcvd: 141

访问这个ip的8080/metrics接口可以看到相关的数据

shell 复制代码

[root@k8s-master01 ~]# curl -s 10.100.85.200:8080/metrics |head
# HELP kube_certificatesigningrequest_labels Kubernetes labels converted to Prometheus labels.
# TYPE kube_certificatesigningrequest_labels gauge
# HELP kube_certificatesigningrequest_created Unix creation timestamp
# TYPE kube_certificatesigningrequest_created gauge
# HELP kube_certificatesigningrequest_condition The number of each certificatesigningrequest condition
# TYPE kube_certificatesigningrequest_condition gauge
# HELP kube_certificatesigningrequest_cert_length Length of the issued cert
# TYPE kube_certificatesigningrequest_cert_length gauge
# HELP kube_configmap_info Information about configmap.
# TYPE kube_configmap_info gauge

本节重点总结 :

k8s 会为service创建cordns解析
pod中dns的搜索域
模拟prometheus进行dns解析后访问数据