Nginx Ingress returns 502 Bad Gateway on Kubernetes

Question

I have a Kubernetes cluster deployed on AWS (EKS). I deployed the cluster using the “eksctl” command line tool. I’m trying to deploy a Dash python app on the cluster without success. The default port for Dash is 8050. For the deployment I used the following resources:

pod
service (ClusterIP type)
ingress

You can check the resource configuration files below:

pod-configuration-file.yml

kind: Pod
apiVersion: v1
metadata:
  name: dashboard-app
  labels:
    app: dashboard
spec:
  containers:
    - name: dashboard
      image: my_image_from_ecr
      ports:
        - containerPort: 8050

service-configuration-file.yml

kind: Service
apiVersion: v1
metadata:
  name: dashboard-service
spec:
  selector:
    app: dashboard
  ports:
    - port: 8050 # exposed port
      targetPort: 8050

ingress-configuration-file.yml (host based routing)

kind: Ingress
metadata:
  name: dashboard-ingress
  annotations:
    nginx.ingress.kubernetes.io/ssl-redirect: "false"
    nginx.ingress.kubernetes.io/force-ssl-redirect: "false"
    nginx.ingress.kubernetes.io/rewrite-target: /
spec:
  rules:
  - host: dashboard.my_domain
    http:
      paths:
      - backend:
          serviceName: dashboard-service
          servicePort: 8050
        path: /

I followed the steps below:

kubectl apply -f pod-configuration-file.yml
kubectl apply -f service-configuration-file.yml
kubectl apply -f ingress-confguration-file.yml

I also noticed that the pod deployment works as expected:

kubectl logs my_pod:

and the output is:

Dash is running on http://127.0.0.1:8050/

 Warning: This is a development server. Do not use app.run_server
 in production, use a production WSGI server like gunicorn instead.

 * Serving Flask app "annotation_analysis" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: on

You can see from the ingress configuration file that I want to do host based routing using my domain. For this to work, I have also deployed an nginx-ingress. I have also created an “A” record set using Route53 that maps the “dashboard.my_domain” to the nginx-ingress:

kubectl get ingress

and the output is:

NAME                           HOSTS                                            ADDRESS.           PORTS.   AGE                                                            
dashboard-ingress         dashboard.my_domain                  nginx-ingress.elb.aws-region.amazonaws.com   80      93s

Moreover,

kubectl describe ingress dashboard-ingress

and the output is:

Name:             dashboard-ingress
Namespace:        default
Address:          nginx-ingress.elb.aws-region.amazonaws.com
Default backend:  default-http-backend:80 (<error: endpoints "default-http-backend" not found>)
Rules:
  Host                                            Path  Backends
  ----                                            ----  --------
  host.my-domain  
                                              /   dashboard-service:8050 (192.168.36.42:8050)
Annotations:                                      
nginx.ingress.kubernetes.io/force-ssl-redirect: false
                                              
nginx.ingress.kubernetes.io/rewrite-target: /
                                              
nginx.ingress.kubernetes.io/ssl-redirect: false
Events:                                           <none>

Unfortunately, when I try to access the Dash app on the browser, I get a 502 Bad Gateway error from the nginx. Could you please help me because my Kubernetes knowledge is limited. Thanks in advance.

I type dashboard.my_domain on browser. See "kubectl get ingress". The problem is really weird. I followed exactly the same process for a "Flask server (port 5000)" and it works. Thanks for your help btw. — P. Str

P. Str P. Str · Accepted Answer · 2020-07-27T15:32:06

It had nothing to do with Kubernetes or AWS settings. I had to change my python Dash code from:

if __name__ == "__main__":
    app.run_server(debug=True)

to:

if __name__ == "__main__":
    app.run_server(host='0.0.0.0',debug=True).

The addition of host='0.0.0.0' did the trick!

Nginx Ingress returns 502 Bad Gateway on Kubernetes

2 Answers