<p>The Istio ingress gateway exposes the following ports by default:</p>

<pre><code>80:31380/TCP,443:31390/TCP,31400:31400/TCP
</code></pre>

<p>Why does it expose 31400 and map it to 31400? I can't find an explanation of this in the docs or elsewhere.</p>

<p><strong>Background:</strong> I'm following the <a href="https://istio.io/docs/setup/kubernetes/helm-install/#option-1-install-with-helm-via-helm-template" rel="noreferrer">Install with Helm via <code>helm template</code></a> guide using Istio 0.8.0. The deployment manifest is built from <a href="https://github.com/istio/istio/tree/0.8.0/install/kubernetes/helm/istio" rel="noreferrer">https://github.com/istio/istio/tree/0.8.0/install/kubernetes/helm/istio</a>, giving the following ingress gateway service definition:</p>

<pre><code># Source: istio/charts/ingressgateway/templates/service.yaml
apiVersion: v1
kind: Service
metadata:
  name: istio-ingressgateway
  namespace: istio-system    
  labels:
    chart: ingressgateway-0.8.0
    release: istio
    heritage: Tiller
    istio: ingressgateway
spec:
  type: NodePort
  selector:
    istio: ingressgateway
  ports:
    -
      name: http
      nodePort: 31380
      port: 80
    -
      name: https
      nodePort: 31390
      port: 443
    -
      name: tcp
      nodePort: 31400
      port: 31400
</code></pre>

<p><a href="https://github.com/istio/istio/commit/a4b6cc55dd2066f6c2bbe8fdf6d39657f44f444e" rel="noreferrer">Commit a4b6cc5</a> mentions:</p>

<blockquote>
  <p>Adding the 31400 port back because of testdata dependency</p>
</blockquote>

<p>This is part of <a href="https://github.com/istio/istio/pull/6350" rel="noreferrer"><code>istio/istio</code> PR 6350</a></p>

<blockquote>
  <p>These changes add support for multiple ingress/egress gateway configuration in the Helm charts.<br>
  The new gateways field is an array that by default has one configuration (as it was before) but allows users to add more configurations to have multiple ingress/egress gateways deployed when installing the charts.</p>
</blockquote>

<p>See <a href="https://github.com/istio/istio/pull/6350/commits/05cba4e6570c1350a6b532355b7b4cc9c857c8e7" rel="noreferrer">commit 05cba4e</a>.</p>
