Couldn't Make Django Talk with Postgres in k8s

I have a deployment of a simple Django app in minikube. It has two containers one for the Django app and one for postgres db. It is working with docker-compose, but couldn't make it work in minikube k8s cluster. When I opened a terminal to the container and ping the service it wasn't successful. I didn't find what causes this communication error.

It's a basic app that just has a login page for signing in or signing up. After signing in you can create some notes. After I deployed to minikube I was able to access 127.0.0.1:8000, but when I enter the information to sign up it gave the error below. Apparently, it couldn't store data in the db.

DATABASES part in settings.py in django project:

DATABASES = {
'default': {
    'ENGINE': 'django.db.backends.postgresql_psycopg2',
    'NAME': 'postgres',
    'USER': 'postgres',
    'PASSWORD': 'postgres',
    'HOST': 'db',
    'PORT': '5432',
}
}

Dockerfile for building the image for the app:

FROM python:2.7

WORKDIR /notejam

COPY ./ ./

RUN pip install -r requirements.txt

EXPOSE 8000

CMD python manage.py runserver 0.0.0.0:8000

Deployment file:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: notejam-deployment
  labels: 
    app: notejam-app
spec:
  selector:
    matchLabels:
      app: notejam-app
  template:
    metadata:
      labels:
        app: notejam-app
    spec:
      volumes:
        - name: postgres-pvc
          persistentVolumeClaim:
            claimName: postgres-pvc
      containers:
      - name: notejam
        image: notejam_k8s
        imagePullPolicy: Never
        resources:
          limits:
            memory: "128Mi"
            cpu: "500m"
        ports:
        - containerPort: 8000
      - name: postgres-db
        image: postgres
        imagePullPolicy: Never
        ports:
        - containerPort: 5432
        resources:
          limits:
            memory: "128Mi"
            cpu: "500m"
        env:
        - name: POSTGRES_USERNAME
          valueFrom:
            configMapKeyRef:
              name: postgres-configmap
              key: postgres-username
        - name: POSTGRES_PASSWORD
          valueFrom:
            secretKeyRef:
              name: postgres-secret
              key: postgres-password
        - name: POSTGRES_DB
          valueFrom:
            configMapKeyRef:
              name: postgres-configmap
              key: postgres-db
        volumeMounts:
          - mountPath: /notejam-db
            name: postgres-pvc
---
apiVersion: v1
kind: Service
metadata:
  name: db
spec:
  selector:
    app: notejam-app
  ports:
  - port: 5432
    targetPort: 5432
---
apiVersion: v1
kind: Service
metadata:
  name: notejam-external-service
spec:
  selector:
    app: notejam-app
  type: LoadBalancer
  ports:
  - protocol: TCP 
    port: 8000
    targetPort: 8000

Error:

OperationalError at /signup/

could not connect to server: Connection timed out
    Is the server running on host "db" (10.96.150.207) and accepting
    TCP/IP connections on port 5432?

Request Method:     POST
Request URL:    http://127.0.0.1:8000/signup/
Django Version:     1.6.5
Exception Type:     OperationalError
Exception Value:    

could not connect to server: Connection timed out
    Is the server running on host "db" (10.96.150.207) and accepting
    TCP/IP connections on port 5432?

Exception Location:     /usr/local/lib/python2.7/site-packages/psycopg2/__init__.py in connect, line 127
Python Executable:  /usr/local/bin/python
Python Version:     2.7.18
Python Path:    

['/notejam',
'/usr/local/lib/python27.zip',
'/usr/local/lib/python2.7',
'/usr/local/lib/python2.7/plat-linux2',
'/usr/local/lib/python2.7/lib-tk',
'/usr/local/lib/python2.7/lib-old',
'/usr/local/lib/python2.7/lib-dynload',
'/usr/local/lib/python2.7/site-packages']

Server time:    Thu, 26 Aug 2021 00:40:58 +0300