Installing, configuring 3 node Kubernetes(master) cluster on CentOS 7.5 – Adding CoreDNS as part of the Kubernetes cluster
In
Part 4 I described how to install and configure the kubernetes manifest and kubelet service, below we are going to add the newly addition CoreDNS to your Kubernetes cluster.
This is
Part 5 – Adding CoreDNS as part of the Kubernetes cluster.
Adding configuring CoreDNS
Lets begin by downloading the latest CoreDNS version.
cd /var/tmp
curl -o coredns_1.2.0_linux_amd64.tgz https://github.com/coredns/coredns/releases/download/v1.2.0/coredns_1.2.0_linux_amd64.tgz
tar zxf coredns_1.2.0_linux_amd64.tgz
Note: to get the latest release click
here.
After extracting the gz file, you will find a
deployment directory.
In the
deployment we are mostly interested in the
kubernetes
in the
kubernetes directory you will find a
deployment script and a yaml file.
You can use the deployment script
deploy.sh somthink like the the below, or modify the yaml file your self and just run kubectl to deploy the config.
# deploy script
./deploy.sh -r 10.3.0.0/21 -r 10.20.0.0/20 -i 10.3.0.10 | kubectl apply -f -
# OR run - kubectl apply..
kubectl apply -f coredns.yaml.sed
Below is the
coredns.yaml I have successfully used.
cat coredns.yaml
apiVersion: v1
kind: ConfigMap
metadata:
name: coredns
namespace: kube-system
data:
Corefile: |
.:53 {
errors
log
health
kubernetes cluster.local 10.20.0.0/20 10.3.0.0/21 {
upstream 8.8.8.8 8.8.4.4
pods insecure
fallthrough
}
prometheus :9153
proxy . /etc/resolv.conf
cache 30 cluster.local 10.20.0.0/20 10.3.0.0/21
reload
loadbalance
}
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: coredns
namespace: kube-system
labels:
k8s-app: kube-dns
kubernetes.io/name: "CoreDNS"
spec:
replicas: 2
strategy:
type: RollingUpdate
rollingUpdate:
maxUnavailable: 1
selector:
matchLabels:
k8s-app: kube-dns
template:
metadata:
labels:
k8s-app: kube-dns
spec:
tolerations:
- key: "CriticalAddonsOnly"
operator: "Exists"
containers:
- name: coredns
image: coredns/coredns:1.2.0
imagePullPolicy: IfNotPresent
args: [ "-conf", "/etc/coredns/Corefile" ]
volumeMounts:
- name: config-volume
mountPath: /etc/coredns
readOnly: true
ports:
- containerPort: 53
name: dns
protocol: UDP
- containerPort: 53
name: dns-tcp
protocol: TCP
- containerPort: 9153
name: metrics
protocol: TCP
securityContext:
allowPrivilegeEscalation: false
capabilities:
add:
- NET_BIND_SERVICE
drop:
- all
readOnlyRootFilesystem: true
livenessProbe:
httpGet:
path: /health
port: 8080
scheme: HTTP
initialDelaySeconds: 60
timeoutSeconds: 5
successThreshold: 1
failureThreshold: 5
dnsPolicy: Default
volumes:
- name: config-volume
configMap:
name: coredns
items:
- key: Corefile
path: Corefile
---
apiVersion: v1
kind: Service
metadata:
name: kube-dns
namespace: kube-system
annotations:
prometheus.io/port: "9153"
prometheus.io/scrape: "true"
labels:
k8s-app: kube-dns
kubernetes.io/cluster-service: "true"
kubernetes.io/name: "CoreDNS"
spec:
selector:
k8s-app: kube-dns
clusterIP: 10.3.0.10
ports:
- name: dns
port: 53
protocol: UDP
- name: dns-tcp
port: 53
protocol: TCP
Just run the below to apply and configure, this will launch 2 instances of CoreDNS.
kubectl apply -f coredns.yaml
Below is the kubectl output of my cluster after adding CoreDNS.
kubectl get all --all-namespaces -o wide
NAMESPACE NAME READY STATUS RESTARTS AGE IP NODE
kube-system pod/coredns-58c8c868b7-84d5q 1/1 Running 0 3d 10.20.2.31 kmaster2
kube-system pod/coredns-58c8c868b7-jkg4h 1/1 Running 0 3d 10.20.3.41 kmaster1
kube-system pod/kube-apiserver-kmaster1 1/1 Running 6 4d 172.20.0.11 kmaster1
kube-system pod/kube-apiserver-kmaster2 1/1 Running 9 7d 172.20.0.12 kmaster2
kube-system pod/kube-apiserver-kmaster3 1/1 Running 11 11d 172.20.0.13 kmaster3
kube-system pod/kube-controller-manager-kmaster1 1/1 Running 6 4d 172.20.0.11 kmaster1
kube-system pod/kube-controller-manager-kmaster2 1/1 Running 9 7d 172.20.0.12 kmaster2
kube-system pod/kube-controller-manager-kmaster3 1/1 Running 11 11d 172.20.0.13 kmaster3
kube-system pod/kube-proxy-kmaster1 1/1 Running 6 4d 172.20.0.11 kmaster1
kube-system pod/kube-proxy-kmaster2 1/1 Running 5 7d 172.20.0.12 kmaster2
kube-system pod/kube-proxy-kmaster3 1/1 Running 6 7d 172.20.0.13 kmaster3
kube-system pod/kube-scheduler-kmaster1 1/1 Running 6 4d 172.20.0.11 kmaster1
kube-system pod/kube-scheduler-kmaster2 1/1 Running 9 7d 172.20.0.12 kmaster2
kube-system pod/kube-scheduler-kmaster3 1/1 Running 11 11d 172.20.0.13 kmaster3
NAMESPACE NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE SELECTOR
default service/kubernetes ClusterIP 10.3.0.1 443/TCP 11d
kube-system service/kube-dns ClusterIP 10.3.0.10 53/UDP,53/TCP 3d k8s-app=kube-dns
NAMESPACE NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE CONTAINERS IMAGES SELECTOR
kube-system deployment.apps/coredns 2 2 2 2 3d coredns coredns/coredns:1.2.0 k8s-app=kube-dns
NAMESPACE NAME DESIRED CURRENT READY AGE CONTAINERS IMAGES SELECTOR
kube-system replicaset.apps/coredns-58c8c868b7 2 2 2 3d coredns coredns/coredns:1.2.0 k8s-app=kube-dns,pod-template-hash=1474742463
To test DNS working you can do something like the below.
To see full dns logs run the below.
Note: logs are turned on for everything, you might wont to change that once configured.
kubectl -n kube-system log pod/coredns-58c8c868b7-jkg4h --follow &
# After running the below dns tools example, output should look something like the below.
10.20.3.1:47126 - [14/Aug/2018:16:08:10 +0000] 5457 "AAAA IN kubernetes.default.svc.cluster.local. udp 54 false 512" NOERROR qr,aa,rd,ra 147 0.000114994s
Next, lets start a pod called dnstools from infoblox, you do so by running the below.
Note: Infoblox has create a very good small image ready with all dns testing tools you might need.
kubectl run -it --rm --restart=Never --image=infoblox/dnstools:latest dnstools
If you don't see a command prompt, try pressing enter.
dnstools# nslookup kubernetes
Server: 10.3.0.10
Address: 10.3.0.10#53
Name: kubernetes.default.svc.cluster.local
Address: 10.3.0.1
Congratulations, you now have a working Kubernetes CoreDNS configured.
CoreDNS has great list of documents at
the CoreDNS website, as well as a list available
Plugins to extend feature functionality.
In
Part 6 will continue Adding / Configuring Kubernetes worker nodes (coming soon).
You might also like –
Other related articles to Docker and Kubernetes / micro-service.
Like what you’re reading? please provide feedback, any feedback is appreciated.
Loading...