I have two deployments one for backend and other for frontend both deployed on the Kubernetes cluster.

BackendDeployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: backend-deployement
  labels:
    app: backend-kube
spec:
  replicas: 1
  selector:
    matchLabels:
      app: backend-app-kube
  template:
    metadata:
      labels:
        app: backend-app-kube
    spec:
      containers:
        - name: backend-kube-image
          image: fxx/frox-backend-kube
          ports:
            - containerPort: 8111

BackendService.yaml

apiVersion: v1
kind: Service
metadata:
  name: backend-app-kube-service
spec:
  selector:
    app: backend-app-kube
  ports:
    - protocol: TCP
      port: 8111
      targetPort: 8111

Backend is getting deployed perfectly

FrontendDeployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: frontend-deployement
  labels:
    app: frontend-kube
spec:
  replicas: 1
  selector:
    matchLabels:
      app: fronted-app-kube
  template:
    metadata:
      labels:
        app: fronted-app-kube
    spec:
      containers:
        - name: fronted-kube-image
          image: fxx/frox-front-kube
          ports:
            - containerPort: 80

FrontendService.yaml

apiVersion: v1
kind: Service
metadata:
  name: fronted-app-kube-service
spec:
  selector:
    app: fronted-app-kube
  type: NodePort
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80

Kubernetes documentation suggested Now that you have your backend, you can create a frontend that connects to the backend. The frontend connects to the backend worker Pods by using the DNS name given to the backend Service.

https://kubernetes.io/docs/tasks/access-application-cluster/connecting-frontend-backend/

nginx.conf

server {
    listen       80;
    server_name  localhost;
    location / {
        root   /usr/share/nginx/html;
        index  index.html index.htm;
        try_files $uri /index.html;                 
    }
    location /api {
    proxy_pass http://backend-app-kube-service;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection ‘upgrade’;
    proxy_set_header Host $host;
    proxy_cache_bypass $http_upgrade;
    }
    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   /usr/share/nginx/html;
    }
}

Now when i am creating the frontend deployment it gives me error in container construction [emerg] 1#1: host not found in upstream

Can somebody please give the solution How can I make frontend to talk to backend using Nginx