Kubernetes service : Connection refused when nginx container is serving static files

When curl is made inside pod on port 80, response is fine.
Calling curl outside container via Kubernetes service on machines IP and port 30803, sporadically "Connection refused" appears.

nginx app config:

server {
        listen  80;
        server_name 127.0.0.1;
        access_log  /var/log/nginx/access.log;
        error_log   /var/log/nginx/error.log;
        root        /usr/share/nginx/html;
        index index.html;

       error_page 404 /404.html;
            location = /40x.html {
        }

        error_page 500 502 503 504 /50x.html;
            location = /50x.html {
        }
    }

Kubernetes deployments and service manifest which is used:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-app
  namespace: dev
  labels:
    environment: dev
spec:
  selector:
      matchLabels:
         environment: dev
  replicas: 1
  template:
    metadata:
      labels:
        environment: dev
    spec:
      containers:
      - name: web-app
        imagePullPolicy: Never
        image: web-app:$BUILD_ID
        ports:
          - containerPort: 80
        readinessProbe:
          httpGet:
            path: /
            port: 80
          periodSeconds: 5
---
apiVersion: v1
kind: Service
metadata:
  name: web-app-dev-svc
  namespace: dev
  labels:
    environment: dev
spec:
  selector:
    environment: dev
  type: NodePort
  ports:
  - name: http
    nodePort: 30803
    port: 80
    protocol: TCP
    targetPort: 80

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Source: Docker Questions