if you external service have DNS name domain you can use the external service in kubernetes.

so flow will be something like :

ingress > service > external service 

apiVersion: v1
kind: Service
metadata:
  name: external-service
spec:
  type: ExternalName
  externalName: google.com

now ingress will be something like

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: externalNameservice
spec:
  rules:
  - host: service.example.com
    http:
      paths:
      - backend:
          serviceName: my-service
          servicePort: 80
        path: /

if you want to use the IP address you can go with your approach only

apiVersion: v1
kind: Service
metadata:
  name: external-ip
spec:
  ports:
  - name: app
    port: 80
    protocol: TCP
    targetPort: 5678
  clusterIP: None
  type: ClusterIP

---
apiVersion: v1
kind: Endpoints
metadata:
  name: external-ip
subsets:
- addresses:
  - ip: 172.217.21.14
  ports:
  - name: app
    port: 80
    protocol: TCP

check the service clusterIP also check for the SSL annotation

nginx.ingress.kubernetes.io/ingress.class: "nginx"
    nginx.ingress.kubernetes.io/ssl-redirect: "false"

UPdate :

as you mention if you want to redirect or rewrite the traffic I am just sharing a small example for both

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  annotations:
    kubernetes.io/ingress.class: nginx
    cert-manager.io/cluster-issuer: wordpress-prod
    nginx.ingress.kubernetes.io/configuration-snippet: |
      if ($host = 'www.example.io' ) {
        rewrite ^ https://example.io$request_uri permanent;
      }
      if ($scheme = http) {
        return 301 https://exmple.io$request_uri;
      }
      if ($scheme = 'http') {
        return 301 https://example.io$request_uri;
      }
    nginx.ingress.kubernetes.io/force-ssl-redirect: "True"
    nginx.ingress.kubernetes.io/from-to-www-redirect: "True"
    nginx.ingress.kubernetes.io/server-snippet: |
      location ~ /test-check {
         rewrite /test-check https://app.example.io$uri permanent;
      }
      location = /login {
         rewrite / https://app.example.io/login permanent;
      }
  name: wordpress-prod-ingress
  namespace: default
spec:
  rules:
  - host: example.io
    http:
      paths:
      - backend:
          serviceName: wordpress-site
          servicePort: 80
        path: /
  - host: www.example.io
    http:
      paths:
      - backend:
          serviceName: wordpress-site
          servicePort: 80
        path: /
  tls:
  - hosts:
    - example.io
    - www.example.io
    secretName: www-ssl-certificate