k8s部署时coredns出现CrashLoopBackOff的错误的解决方案

问题描述

之前做项目时要用k8s去搭一个集群。本人纯新手小白，就按照网上的搭建步骤一步步往下做（部署的过程参考 链接网址）
在查看集群内各pod状态时，发现了coredns没有启动成功，一直处于CrashLoopBackOff状态，陷入了不停错误重启的死循环中

[[email protected] a1zMC2]# kubectl get pods -n kube-system
NAME                                 READY   STATUS             RESTARTS   AGE
coredns-bccdc95cf-9wd9n              0/1     CrashLoopBackOff   19         19h
coredns-bccdc95cf-qsf9f              0/1     CrashLoopBackOff   19         19h
etcd-k8s-master                      1/1     Running            3          19h
kube-apiserver-k8s-master            1/1     Running            3          19h
kube-controller-manager-k8s-master   1/1     Running            11         19h
kube-flannel-ds-amd64-sgqsm          1/1     Running            1          16h
kube-flannel-ds-amd64-swqhf          1/1     Running            1          16h
kube-flannel-ds-amd64-tnbmc          1/1     Running            1          16h
kube-proxy-259l8                     1/1     Running            0          16h
kube-proxy-qcnpt                     1/1     Running            0          16h
kube-proxy-rp7qx                     1/1     Running            3          19h
kube-scheduler-k8s-master            1/1     Running            11         19h

解决思路

查看coredns的日志文件，内容如下

[[email protected] a1zMC2]# kubectl logs -f coredns-bccdc95cf-9wd9n -n kube-system
E0512 01:59:03.825489       1 reflector.go:134] github.com/coredns/coredns/plugin/kubernetes/controller.go:317: Failed to list *v1.Endpoints: Get https://10.96.0.1:443/api/v1/endpoints?limit=500&resourceVersion=0: dial tcp 10.96.0.1:443: connect: no route to host
E0512 01:59:03.825489       1 reflector.go:134] github.com/coredns/coredns/plugin/kubernetes/controller.go:317: Failed to list *v1.Endpoints: Get https://10.96.0.1:443/api/v1/endpoints?limit=500&resourceVersion=0: dial tcp 10.96.0.1:443: connect: no route to host
log: exiting because of error: log: cannot create log: open /tmp/coredns.coredns-bccdc95cf-9wd9n.unknownuser.log.ERROR.20210512-015903.1: no such file or directory

再通过kubectl describe pod coredns-bccdc95cf-9wd9n -n kube-system命令查看详情

Events:
  Type     Reason            Age                  From                 Message
  ----     ------            ----                 ----                 -------
  Warning  FailedScheduling  16h (x697 over 17h)  default-scheduler    0/1 nodes are available: 1 node(s) had taints that the pod didn't tolerate.
  Warning  Unhealthy         15h (x5 over 15h)    kubelet, k8s-master  Readiness probe failed: Get http://10.244.0.2:8080/health: net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)
  Warning  Unhealthy         15h (x5 over 15h)    kubelet, k8s-master  Liveness probe failed: Get http://10.244.0.2:8080/health: net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)

感觉应该和host连接出了问题，于是输入cat /etc/resolv.conf查看配置文件。发现里面nameserver那一栏并不是主机master的地址。

抱着试一试的态度，修改它为master节点的IP地址后，再重启docker和kubenet

[[email protected] a1zMC2]# systemctl stop kubelet
[[email protected] a1zMC2]# systemctl stop docker
[[email protected] a1zMC2]# iptables --flush
[[email protected] a1zMC2]# iptables -tnat --flush
[[email protected] a1zMC2]# systemctl start kubelet
[[email protected] a1zMC2]# systemctl start docker

查看一下状态，发现所有的pod可以正常工作了！

[[email protected] a1zMC2]# kubectl get pods -n kube-system
NAME                                 READY   STATUS    RESTARTS   AGE
coredns-bccdc95cf-9wd9n              1/1     Running   21         20h
coredns-bccdc95cf-qsf9f              1/1     Running   21         20h
etcd-k8s-master                      1/1     Running   4          19h
kube-apiserver-k8s-master            1/1     Running   4          19h
kube-controller-manager-k8s-master   1/1     Running   12         19h
kube-flannel-ds-amd64-sgqsm          1/1     Running   1          17h
kube-flannel-ds-amd64-swqhf          1/1     Running   1          17h
kube-flannel-ds-amd64-tnbmc          1/1     Running   2          17h
kube-proxy-259l8                     1/1     Running   0          17h
kube-proxy-qcnpt                     1/1     Running   0          17h
kube-proxy-rp7qx                     1/1     Running   4          20h
kube-scheduler-k8s-master            1/1     Running   12         19h

因为没学过云计算的内容，所以博客中有错误的，欢迎在评论区指正。