Accessing application inside a kubernetes pod from an another application in a different pod - kubernetes

Question

I have a kubernetes cluster having two deployments ui-service-app and user-service-app. Both of the deployments are exposed through Cluster IP services namely ui-service-svc and user-service-svc. In addition there is a Ingress for accessing both of my applications inside those deployments from outside the cluster.
Now I want to make a api call from my application inside ui-service-app to user-service-app. Currently I am using the ingress-ip/user to do so. But there should be some way to do this internally?
apiVersion: apps/v1
kind: Deployment
metadata:
name: user-service-app
labels:
app: user-service-app
spec:
replicas: 1
selector:
matchLabels:
app: user-service-app
template:
metadata:
labels:
app: user-service-app
spec:
containers:
- name: user-service-app
image: <MY-IMAGE-URL>
imagePullPolicy: Always
ports:
- containerPort: 3000
livenessProbe:
httpGet:
path: /ping
port: 3000
readinessProbe:
httpGet:
path: /ping
port: 3000
---
apiVersion: "v1"
kind: "Service"
metadata:
name: "user-service-svc"
namespace: "default"
labels:
app: "user-service-app"
spec:
type: "ClusterIP"
selector:
app: "user-service-app"
ports:
- protocol: "TCP"
port: 80
targetPort: 3000
---
apiVersion: apps/v1
kind: Deployment
metadata:
name: ui-service-app
labels:
app: ui-service-app
spec:
replicas: 1
selector:
matchLabels:
app: ui-service-app
template:
metadata:
labels:
app: ui-service-app
spec:
containers:
- name: ui-service-app
image: <MY-IMAGE-URL>
imagePullPolicy: Always
ports:
- containerPort: 3000
---
apiVersion: "v1"
kind: "Service"
metadata:
name: "ui-service-svc"
namespace: "default"
labels:
app: "ui-service-app"
spec:
type: "ClusterIP"
selector:
app: "ui-service-app"
ports:
- protocol: "TCP"
port: 80
targetPort: 3000
---
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
name: awesome-ingress
annotations:
nginx.ingress.kubernetes.io/rewrite-target: /$2
spec:
ingressClassName: nginx
defaultBackend:
service:
name: ui-service-svc
port:
number: 80
rules:
- http:
paths:
- path: /login
pathType: Prefix
backend:
service:
name: ui-service-svc
port:
number: 80
- path: /user(/|$)(.*)
pathType: Prefix
backend:
service:
name: user-service-svc
port:
number: 80
UPDATE 1:
THIS IS THE ERROR PAGE WHEN I CHANGE THE URL IN REACT APP TO HTTP://USER-SERVICE-SVC

Answer 1

Use the service name of the associated service.
From any other pod in the same namespace, the hostname user-service-svc will map to the Service you've defined, so http://user-service-svc would connect you to the web server of the user-service-app Deployment (no port specified, because your Service is mapping port 80 to container port 3000).
From another namespace, you can use the hostname <service>.<namespace>.svc.cluster.local, but that's not relevant to what you're doing here.
See the Service documentation for more details.