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Introduction to CoreDNS

CoreDNS is actually a DNS service, and DNS is a common means of service discovery, so many open source projects and engineers will use CoreDNS to provide service discovery for the cluster. Kubernetes uses CoreDNS in the cluster to solve the problem of service discovery.

If you want to implement the function of service discovery in a distributed system, CoreDNS is actually a very good choice. CoreDNS, as an application that has entered CNCF and used as a DNS service in Kubernetes, has been proved to be stable and usable. at the same time, its plug-in-based implementation is very lightweight and easy to use, and the use of plug-in chain also makes the definition of third-party plug-ins very convenient.

Coredns architecture the entire CoreDNS service is built on a HTTP/2 Web server Caddy written in Go. Cluster information introduction Kubernetesv1.13 k8s-master172.20.101.157 172.20.101.165 172.20.101.164 CLUSTER_CIDR10.254.0.0/16CLUSTER_DNS10.254.0.10Coredns project download address 1:wget https://github.com/coredns/deployment/archive/master.zipunzip master.zip download address 2:git clone https://github.com/coredns/deployment.git installation and deployment confirm whether there is a running dns service kubectl Get pods-o wide-n=kube-system# delete command kubectl delete-- namespace=kube-system deployment *-dns installation home directory cd / workspace/ download git clone https://github.com/coredns/deployment.git installation directory cd / workspace/deployment/kubernetes View project file [root@node01 kubernetes] # introduction to llCoreDNS-k8s_version.mdcoredns.yaml.seddeploy.shREADME.mdrollback.shScaling_CoreDNS.mdUpgrading_CoreDNS.md important files

Deploy.sh is a tool script used to generate and run the CoreDNS deployment file (manifest) in a cluster that is already running kube-dns. It uses the coredns.yaml.sed file as a template to create a deployment for ConfigMap and CoreDNS, and then updates the selector of existing kube-dns services in the cluster using CoreDNS's deployment. Reusing an existing service does not conflict with the request of the service.

Deploy script uses the method usage:. / deploy.sh [- r REVERSE-CIDR] [- I DNS-IP] [- d CLUSTER-DOMAIN] [- t YAML-TEMPLATE]-r: Define a reverse zone for the given CIDR. You may specifcy this option more than once to add multiple reverse zones. If no reverse CIDRs are defined, then the default is to handle all reverse zones (i.e. In-addr.arpa and ip6.arpa)-I: Specify the cluster DNS IP address. If not specificed, the IP address of the existing "kube-dns" service is used, if present. -s: Skips the translation of kube-dns configmap to the corresponding CoreDNS Corefile configuration.Coredns matches kubernetes version: reference address: https://github.com/coredns/deployment/blob/master/kubernetes/CoreDNS-k8s_version.mdKubernetes v1.14 = > CoreDNS v1.3.1Kubernetes v1.13 = = > CoreDNS v1.2.6

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