How to enable coredns for dns discovery on kubernetes version 1.14?

Question

I have a problem with service (DNS) discovery in kubernetes 1.14 version in ubuntu bionic.

Right now my 2 pods communicating using IP addresses. How can I enable coredns for service (DNS) discovery?

Here is the output of kubectl for service and pods from kube-system namespace:

    kubectl get pods,svc --namespace=kube-system | grep dns
    pod/coredns-fb8b8dccf-6plz2          1/1     Running            0          6d23h
    pod/coredns-fb8b8dccf-thxh6          1/1     Running            0          6d23h
    
    service/kube-dns        ClusterIP   10.96.0.10       <none>        53/UDP,53/TCP,9153/TCP   6d23h

I have installed kubernetes on master node(ubuntu bionic machine) using below steps

    apt-get update
    apt-get install     apt-transport-https     ca-certificates     curl     gnupg-agent     software-properties-common
    curl -fsSL https://download.docker.com/linux/ubuntu/gpg | apt-key add -
    add-apt-repository    "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
    apt-get update
    apt-get install docker-ce docker-ce-cli containerd.io
    apt-get update && apt-get install -y apt-transport-https curl
    curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | apt-key add -
    
    cat <<EOF >/etc/apt/sources.list.d/kubernetes.list
    deb https://apt.kubernetes.io/ kubernetes-xenial main
    EOF
    
    apt-get update
    apt-get install -y kubelet kubeadm kubectl
    kubectl version
    apt-mark hold kubelet kubeadm kubectl
    kubeadm config images pull
    swapoff -a
    kubeadm init
    
    mkdir -p $HOME/.kube
    cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
    chown $(id -u):$(id -g) $HOME/.kube/config
    sysctl net.bridge.bridge-nf-call-iptables=1
    kubectl apply -f "https://cloud.weave.works/k8s/net?k8s-version=$(kubectl version | base64 | tr -d '\n')"
    kubectl get pods --all-namespaces

This is on worker node

    Docker is already installed, so directly installing kubernetes on worker node
    apt-get update && apt-get install -y apt-transport-https curl
    curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | apt-key add -
    cat <<EOF >/etc/apt/sources.list.d/kubernetes.list
    deb https://apt.kubernetes.io/ kubernetes-xenial main
    EOF
    
    apt-get update
    apt-get install -y kubelet kubeadm kubectl
    kubectl version
    apt-mark hold kubelet kubeadm kubectl
    swapoff -a
    Now joined worker node to master

Answer:-

I think everything was setup correctly by default, There was a misunderstanding by me that I can call a server running in one pod from another pod using the container name and port which I have specified in spec, but instead I should use service name and port.

Below is my deployment spec and service spec:-

Deployment spec:-

    apiVersion: extensions/v1beta1
    kind: Deployment
    metadata:
      name: node-server1-deployment
    spec:
      replicas: 1
      template:
    metadata:
      labels:
        app: node-server1
    spec:
      hostname: node-server1
      containers:
      - name: node-server1
        image: bvenkatr/node-server1:1
        ports:
        - containerPort: 5551

Service spec:

    kind: Service
    apiVersion: v1
    metadata:
      name: node-server1-service
    spec:
      selector:
         app: node-server1
      ports:
      - protocol: TCP
        port: 5551

Answer 1

As of Kubernetes v1.12, CoreDNS is the recommended DNS Server, replacing kube-dns. In Kubernetes, CoreDNS is installed with the following default Corefile configuration:

apiVersion: v1
kind: ConfigMap
metadata:
  name: coredns
  namespace: kube-system
data:
  Corefile: |
    .:53 {
        errors
        health
        kubernetes cluster.local in-addr.arpa ip6.arpa {
           pods insecure
           upstream
           fallthrough in-addr.arpa ip6.arpa
        }
        prometheus :9153
        proxy . /etc/resolv.conf
        cache 30
        loop
        reload
        loadbalance
    }

More info yo can find here.

You can verify your env by running:

kubectl get cm coredns -n kube-system -o yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: coredns
  namespace: kube-system

and: kubeadm config view dns: type: CoreDNS

during kubeadm init you should noticed:

[addons] Applied essential addon: CoreDNS

If you are moving from kube-dns to CoreDNS, make sure to set the CoreDNS feature gate to true during an upgrade. For example, here is what a v1.11.0 upgrade would look like: kubeadm upgrade apply v1.11.0 --feature-gates=CoreDNS=true

In Kubernetes version 1.13 and later the CoreDNS feature gate is removed and CoreDNS is used by default. More information here.

You can see if your coredns pod is working properly by running:

kubectl logs <your coredns pod> -n kube-system
.:53
2019-05-02T13:32:41.438Z [INFO] CoreDNS-1.3.1
CoreDNS-1.3.1
.
.