I have built a flask app that I would like to add to a Kubernetes ingress. Currently, I have 2 questions I cannot seem to get my head around:

1. In order for the flask app to be able to handle several requests, I figured I would add gunicorn. Do I need this, or can I mitigate this by using some kind of automatic horizontal scaling and the ingress routing layer handle it? I am new to Kubernetes, and perhaps the solution is simpler than what I am trying below.

2. With the presumption that I do need gunicorn, I have proceeded and added it to the flask docker. The problem I have with this is that I now get a 502 Bad Gateway Error nginx and the log of the pod have not printed any error. If I create a load balancer service instead of the clusterIP I use with the ingress, the flask app with unicorn works fine, just as the flask app does on the ingress without adding gunicorn. I have no idea why hence writing this question. The dockerfile installs all dependencies to run flask and finishes with:

   EXPOSE 8080
   
   CMD ["gunicorn", "--config", "/flaskapp/gunicorn_config.py", "run:app"]

   I have configured my ingress like this:

   apiVersion: v1
   items:
   - apiVersion: extensions/v1beta1
     kind: Ingress
    metadata:
      annotations:
        ingress.bluemix.net/client-max-body-size: 128m
        ingress.bluemix.net/rewrite-path: serviceName=flask-service rewrite=/; 
   spec:
     rules:
     - host: <my-domain>
       http:
         paths:
         - backend:
           serviceName: flask-service
           servicePort: 8080
         path: /flask/
     tls:
     - hosts:
       - <my-domain>
       secretName: <my-secret>
   status:
     loadBalancer:
       ingress:
       - ip: <ip>

   The service looks like this:

   apiVersion: v1
   kind: Service
   metadata:
     name: flask-service
     labels:
       app: flask-service
   spec:
     type: ClusterIP
     ports:
     - port: 8080
       protocol: TCP
     selector:
       app: flask

   The deployment is also very simple specifying the correct image and port.

Given that I need gunicorn(or similar), how can I solve the 502 Bad Gateway Error I get?