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| # CoreDNS in kubernetes | ||
| # CoreDNS in Kubernetes | ||
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| Take me to [Lecture](https://kodekloud.com/courses/certified-kubernetes-administrator-with-practice-tests/lectures/9808285) | ||
| - Take me to [Lecture](https://kodekloud.com/courses/certified-kubernetes-administrator-with-practice-tests/lectures/9808285) | ||
|
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| #### Solution | ||
| In this section, we will take a look at **CoreDNS in the Kubernetes** | ||
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| 1. Check the Solution | ||
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| <details> | ||
| ## To view the Pod | ||
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| ``` | ||
| CoreDNS | ||
| ``` | ||
| </details> | ||
| 2. Check the Solution | ||
| ``` | ||
| $ kubectl get pods -n kube-system | ||
| NAME READY STATUS RESTARTS AGE | ||
| coredns-66bff467f8-2vghh 1/1 Running 0 53m | ||
| coredns-66bff467f8-t5nzm 1/1 Running 0 53m | ||
| ``` | ||
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| <details> | ||
| ## To view the Deployment | ||
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| ``` | ||
| 2 | ||
| ``` | ||
| </details> | ||
| ``` | ||
| $ kubectl get deployment -n kube-system | ||
| NAME READY UP-TO-DATE AVAILABLE AGE | ||
| coredns 2/2 2 2 53m | ||
| ``` | ||
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| 3. Check the Solution | ||
| ## To view the configmap of CoreDNS | ||
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| <details> | ||
| ``` | ||
| $ kubectl get configmap -n kube-system | ||
| NAME DATA AGE | ||
| coredns 1 52m | ||
| ``` | ||
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| ``` | ||
| 10.96.0.10 | ||
| ``` | ||
| </details> | ||
| ## CoreDNS Configuration File | ||
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| 4. Check the Solution | ||
| ``` | ||
| $ kubectl describe cm coredns -n kube-system | ||
| <details> | ||
| Corefile: | ||
| --- | ||
| .:53 { | ||
| errors | ||
| health { lameduck 5s | ||
| } | ||
| ready | ||
| kubernetes cluster.local in-addr.arpa ip6.arpa { | ||
| pods insecure | ||
| fallthrough in-addr.arpa ip6.arpa | ||
| ttl 30 | ||
| } | ||
| prometheus :9153 | ||
| forward . /etc/resolv.conf | ||
| cache 30 | ||
| loop | ||
| reload | ||
| } | ||
| ``` | ||
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| ``` | ||
| /etc/coredns/Corefile | ||
| ## To view the Service | ||
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| OR | ||
| ``` | ||
| $ kubectl get service -n kube-system | ||
| NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE | ||
| kube-dns ClusterIP 10.96.0.10 <none> 53/UDP,53/TCP,9153/TCP 62m | ||
| ``` | ||
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| kubectl -n kube-system describe deployments.apps coredns | grep -A2 Args | grep Corefile | ||
| ``` | ||
| </details> | ||
| ## To view Configuration into the kubelet | ||
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| 5. Check the Solution | ||
| ``` | ||
| $ cat /var/lib/kubelet/config.yaml | grep -A2 clusterDNS | ||
| clusterDNS: | ||
| - 10.96.0.10 | ||
| clusterDomain: cluster.local | ||
| <details> | ||
| ``` | ||
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| ``` | ||
| Configured as a ConfigMapObject | ||
| ``` | ||
| </details> | ||
| ## To view the fully qualified domain name | ||
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| 6. Check the Solution | ||
| - With the `host` command, we will get fully qualified domain name (FQDN). | ||
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| <details> | ||
| ``` | ||
| $ host web-service | ||
| web-service.default.svc.cluster.local has address 10.106.112.101 | ||
| ``` | ||
| CoreDNS | ||
| ``` | ||
| </details> | ||
| $ host web-service.default | ||
| web-service.default.svc.cluster.local has address 10.106.112.101 | ||
| 7. Check the Solution | ||
| $ host web-service.default.svc | ||
| web-service.default.svc.cluster.local has address 10.106.112.101 | ||
| <details> | ||
| $ host web-service.default.svc.cluster.local | ||
| web-service.default.svc.cluster.local has address 10.106.112.101 | ||
| ``` | ||
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| ``` | ||
| coredns | ||
| ``` | ||
| </details> | ||
| ## To view the `/etc/resolv.conf` file | ||
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| 8. Check the Solution | ||
| ``` | ||
| $ kubectl run -it --rm --restart=Never test-pod --image=busybox -- cat /etc/resolv.conf | ||
| nameserver 10.96.0.10 | ||
| search default.svc.cluster.local svc.cluster.local cluster.local | ||
| options ndots:5 | ||
| pod "test-pod" deleted | ||
| ``` | ||
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| <details> | ||
| ## Resolve the Pod | ||
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| ``` | ||
| cluster.local | ||
| ``` | ||
| </details> | ||
| ``` | ||
| $ kubectl get pods -o wide | ||
| NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES | ||
| test-pod 1/1 Running 0 11m 10.244.1.3 node01 <none> <none> | ||
| nginx 1/1 Running 0 10m 10.244.1.4 node01 <none> <none> | ||
| 9. Check the Solution | ||
| $ kubectl exec -it test-pod -- nslookup 10-244-1-4.default.pod.cluster.local | ||
| Server: 10.96.0.10 | ||
| Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local | ||
| <details> | ||
| Name: 10-244-1-4.default.pod.cluster.local | ||
| Address 1: 10.244.1.4 | ||
| ``` | ||
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| ``` | ||
| Ok | ||
| ``` | ||
| </details> | ||
| ## Resolve the Service | ||
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| 10. Check the Solution | ||
| ``` | ||
| $ kubectl get service | ||
| NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE | ||
| kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 85m | ||
| web-service ClusterIP 10.106.112.101 <none> 80/TCP 9m | ||
| <details> | ||
| $ kubectl exec -it test-pod -- nslookup web-service.default.svc.cluster.local | ||
| Server: 10.96.0.10 | ||
| Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local | ||
| ``` | ||
| web-service | ||
| ``` | ||
| </details> | ||
| Name: web-service.default.svc.cluster.local | ||
| Address 1: 10.106.112.101 web-service.default.svc.cluster.local | ||
| 11. Check the Solution | ||
| ``` | ||
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| <details> | ||
| ``` | ||
| web-serivce.default.pod | ||
| ``` | ||
| </details> | ||
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| 12. Check the Solution | ||
| #### References Docs | ||
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| <details> | ||
| ``` | ||
| web-service.payroll | ||
| ``` | ||
| </details> | ||
| 13. Check the Solution | ||
| <details> | ||
| ``` | ||
| web-service.payroll.svc.cluster | ||
| ``` | ||
| </details> | ||
| 14. Check the Solution | ||
| <details> | ||
| ``` | ||
| kubectl edit deploy webapp | ||
| Search for DB_Host and Change the DB_Host from mysql to mysql.payroll | ||
| spec: | ||
| containers: | ||
| - env: | ||
| - name: DB_Host | ||
| value: mysql.payroll | ||
| ``` | ||
| </details> | ||
| 15. Check the Solution | ||
| <details> | ||
| ``` | ||
| kubectl exec -it hr nslookup mysql.payroll > /root/nslookup.out | ||
| ``` | ||
| </details> | ||
| - https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/#services | ||
| - https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/#pods |