Kubernetes internal socket.io connection - kubernetes

Question

I am following this image architecture from K8s
However I can not seem to connect to socket.io server from within the cluster using the service name
Current situation:
From POD B
Can connect directly to App A's pod using WS ( ws://10.10.10.1:3000 ) ✅
Can connect to App A's service using HTTP ( http://orders:8000 ) ✅
Can not connect to App A's service using WS ( ws://orders:8000 ) ❌
From outside world / Internet
Can connect to App A's service using WS ( ws://my-external-ip/orders ) ✅ // using traefik to route my-external-ip/orders to service orders:8000
Can connect to App A's service using HTTP ( http://my-external-ip/orders ) ✅ // using traefik to route my-external-ip/orders to service orders:8000
My current service configuration
spec:
ports:
- name: http
protocol: TCP
port: 8000
targetPort: 3000
selector:
app: orders
clusterIP: 172.20.115.234
type: ClusterIP
sessionAffinity: None
My Ingress Helm chart
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
name: {{ template "app.name" $ }}-backend
annotations:
kubernetes.io/ingress.class: traefik
ingress.kubernetes.io/auth-type: forward
ingress.kubernetes.io/auth-url: "http://auth.default.svc.cluster.local:8000/api/v1/oauth2/auth"
ingress.kubernetes.io/auth-response-headers: authorization
labels:
{{- include "api-gw.labels" $ | indent 4 }}
spec:
rules:
- host: {{ .Values.deploy.host | quote }}
http:
paths:
- path: /socket/events
backend:
serviceName: orders
servicePort: 8000
My Service Helm chart
apiVersion: v1
kind: Service
metadata:
name: {{ template "app.name" . }}
spec:
{{ if not $isDebug -}}
selector:
app: {{ template "app.name" . }}
{{ end -}}
type: NodePort
ports:
- name: http
port: {{ template "app.svc.port" . }}
targetPort: {{ template "app.port" . }}
nodePort: {{ .Values.service.exposedPort }}
protocol: TCP
# Helpers..
# {{/* vim: set filetype=mustache: */}}
# {{- define "app.name" -}}
# {{ default "default" .Chart.Name }}
# {{- end -}}
# {{- define "app.port" -}}
# 3000
# {{- end -}}
# {{- define "app.svc.port" -}}
# 8000
# {{- end -}}

Answer 1

The services DNS name must be set in your container to access its VIP address.
Kubernetes automatically sets environmental variables in all pods which have the same selector as the service.
In your case, all pods with selector A, have environmental variables set in them when the container is deploying, that contain the services VIP and PORT.
The other pod with selector B, is not linked as an endpoints for the service, therefor, it does not contain the environmental variables needed to access the service.
Here is the k8s documentation related to your problem.
To solve this, you can setup a DNS service, which k8s offers as a cluster addon.
Just follow the documentation.