I have Nodejs application running in K8S ( Minikube running in hyperv) , the application connecting to DB.
This DB is running also in k8S as MySQL.
Nodejs DB Connection

var mysql = require('mysql');
var connection = mysql.createConnection({
    host: "mysql" ,//work only if you get the ip of the mysql running pod ! need to exec the pod the get the ip
    user:'root',
    password:'root',
    database:'crud'
});
connection.connect(function(error){
    if(!!error) {
        console.log(error);
    } else {
        console.log('Connected..!');
    }
});

module.exports = connection;

as you can see I use "host: "mysql" and the nodejs logs show me that the NodeJs application recognize what it "mysql" dns name becuse i have clusterIP service for it

errno: -111,
  code: 'ECONNREFUSED',
  syscall: 'connect',
  address: '10.102.140.203',
  port: 3306,
  fatal: true

this IP address (10.102.140.203) that I see in the log is the CluserIP address of the MySQL service

NAME          TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)          AGE
app           ClusterIP   10.111.211.9     <none>        3000/TCP         62m
appnodeport   NodePort    10.99.179.176    <none>        3000:30958/TCP   62m
kubernetes    ClusterIP   10.96.0.1        <none>        443/TCP          71m
mysql         ClusterIP   10.102.140.203   <none>        3306/TCP         62m
mysqlnode     NodePort    10.106.157.92    <none>        3306:31186/TCP   57m

BUT if I enter the pod himself of the SQL and get the IP address , 172.x.x.x and enter it to the NodeJS DB connection

host: "172.x.x.x.x" 
user:'root',
password:'root',
database:'crud'

the NodeJS application connected fine , but i dont want to do it in this way becuse the ip of the pod himself changes sometimes if the pod is restarting , i want to use service name or something that is not changes.

NodeJS Deployment Yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  annotations:
    kompose.cmd: C:\Users\xx\Desktop\xx\kompose.exe convert
    kompose.version: 1.24.0 (7c629530)
  creationTimestamp: null
  labels:
    io.kompose.service: app
  name: app
spec:
  replicas: 1
  selector:
    matchLabels:
      io.kompose.service: app
  strategy: {}
  template:
    metadata:
      annotations:
        kompose.cmd: C:\Users\xx\Desktop\xx\kompose.exe convert
        kompose.version: 1.24.0 (7c629530)
      creationTimestamp: null
      labels:
        io.kompose.service: app
    spec:
      containers:
        - image: xxx/app:6
          name: employees-app
          ports:
            - containerPort: 3000
          imagePullPolicy: Always
          resources: {}
      hostname: app
      restartPolicy: Always
status: {}

NodeJS Service yaml

apiVersion: v1
kind: Service
metadata:
  annotations:
    kompose.cmd: C:\Users\xxx\Desktop\xxx\kompose.exe convert
    kompose.version: 1.24.0 (7c629530)
  creationTimestamp: null
  labels:
    io.kompose.service: app
  name: app
spec:
  ports:
    - name: "3000"
      port: 3000
      targetPort: 3000
  selector:
    io.kompose.service: app
status:
  loadBalancer: {}

MySQL deployment yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: mysql
spec:
  selector:
    matchLabels:
      app: mysql
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: mysql
    spec:
      containers:
      - image: mysql:5.6
        name: mysql
        env:
          # Use secret in real usage
        - name: MYSQL_ROOT_PASSWORD
          value: "root"
        ports:
        - containerPort: 3306
          name: mysql
        volumeMounts:
        - mountPath: '/var/lib/mysql'
          name: mysql-persistent-storage
      hostname: mysql
      volumes:
      - name: mysql-persistent-storage
        persistentVolumeClaim:
          claimName: mysql-pv-claim

mySQL service

apiVersion: v1
kind: Service
metadata:
  annotations:
    kompose.cmd: C:\Users\xxx\Desktop\xxx\kompose.exe convert
    kompose.version: 1.24.0 (7c629530)
  creationTimestamp: null
  labels:
    io.kompose.service: mysql
  name: mysql
spec:
  ports:
    - name: "3306"
      port: 3306
      targetPort: 3306
  selector:
    io.kompose.service: mysql
status:
  loadBalancer: {}