k8s not able to reach the database

Here is my docker image

FROM mcr.microsoft.com/dotnet/core/aspnet:2.2-alpine3.8 AS base
WORKDIR /app
EXPOSE 80
EXPOSE 443
COPY ./xyz/publish .
ENV ASPNETCORE_URLS=https://+:443;http://+80
ENTRYPOINT ["dotnet","abc/xyz.dll"]

Here is my Deployment.yaml file

apiVersion: apps/v1
kind: Deployment
metadata:
  name: xyzdemo
  namespace: default
spec:
  replicas: 1
  selector:
    matchLabels:
      papi: web
  template:
    metadata:
      labels:
        papi: web
    spec:
      containers:
      - name: xyzdemo-site
        image: xyz.azurecr.io/abc:31018
        ports:
        - containerPort: 443
      imagePullSecrets:
      - name: secret
---
apiVersion: v1
kind: Service
metadata:
  name: xyzdemo-entrypoint
  namespace: default
spec:
  type: LoadBalancer
  selector:
    papi: web
  ports:
  - port: 44328
    targetPort: 443

Here is my appsettings file

 "Server": "xyz.database.windows.net",
  "Database": "pp",
  "User": "ita",
  "Password": "password",

using all these i deployed the application in to the k8s cluster and am able to open the application from the browser, however when i try to get the info from the database, application is getting the network related error after a while.

System.Data.SqlClient.SqlException (0x80131904): A network-related or instance-specific error occurred while establishing a connection to SQL Server

I tried going inside to POD and did the ls command, i can see my application setting file as well as when Cat the application settings, i can see the correct credentials and i dont know what to do and not sure why is not able to connect to the database.

So finally i tried adding the sql connections as the env variables to the pod , then it started working. when i remove those its not connecting.

Now i removed the env variables which has the sql connections then did the log on the pod.
it says can't connect to the database: 'Empty' and server: 'Empty' not sure why is it taking the empty when it has the details inside the applicationsettings.json file.

Well, I do not see what is the config for your k8's application to connect to database. Importantly, where is your database hosted? How can papi:web connect to database?

I also suspect your service is not having appropriate port re-direction. From your service.yaml above, https port of 443 is internally mapped to 44328. What is 44328? What is listening on that port? Your application seems to have no mention of 44328. (Refer Dockerfile)

I would improvise your service.yaml to look something like this:

apiVersion: v1
kind: Service
metadata:
  name: xyzdemo-entrypoint
  namespace: default //This is inferred anyways
spec:
  selector:
    papi: web
  ports:
    - name: http
      protocol: TCP
      port: 80
      targetPort: xxxx //Where your web-server is listening. (From your dockerfile, this is also 80 but it can be any valid TCP port)
    - name: https
      protocol: TCP
      port: 443
      targetPort: xxxx //https for your web-server. (From your dockerfile, this is also 443. Again, can be any TCP port)

Opening up database server to internet is not a good practise. It's a big security threat. Good pattern is to facilitate your web-server communicate to database-server via internal dns that k8's maintain (This is assuming your database server is also a container - something like kubedb. If not, you're database server will have to be available via some sort of proxy that whitelists known hosts and only allows known hosts. eg - cloudsql proxy in GCP).

Depending on how your database server is hosted, you'll have to configure your db config to allow or whitelist your containerised application (The IP you get after applying service.yaml) Only then will your k8's app be able to talk/achieve connectivity to respective db.