analysis message IST0150 (#10590)

* analysis message IST0150

* add message to analysis.yaml

* analysis message IST0150

* add message to analysis.yaml

* modify link example

* remove trailing space

* Update content/en/docs/reference/config/analysis/ist0150/index.md

Co-authored-by: Eric Van Norman <ericvn@us.ibm.com>

Co-authored-by: Eric Van Norman <ericvn@us.ibm.com>

content/en/docs/reference/config/analysis/ist0150/index.md

@@ -0,0 +1,41 @@
+---
+title: ExternalNameServiceTypeInvalidPortName
+layout: analysis-message
+owner: istio/wg-user-experience-maintainers
+test: no
+---
+
+This message occurs for services of type ExternalName when the port doesn't follow Istio service port naming convention, the port is unnamed or the port is named tcp.
+
+## Example
+
+You will receive this message:
+
+{{< text plain >}}
+Warning [IST0150] (Service nginx.default) Port name for ExternalName service is invalid. Proxy may prevent tcp named ports and unmatched traffic for ports serving TCP protocol from being forwarded correctly.
+{{< /text >}}
+
+when your cluster has the following service:
+
+{{< text yaml >}}
+apiVersion: v1
+kind: Service
+metadata:
+  name: nginx
+spec:
+  externalName: nginx.example.com
+  ports:
+  - name: tcp
+    port: 443
+    protocol: TCP
+    targetPort: 443
+  type: ExternalName
+{{< /text >}}
+
+In this example, the port name `tcp` follows the syntax: `name: <protocol>`. However, for ExternalName services, there is no service IP defined, so the SNI field is needed for routing.
+
+## How to resolve
+
+- If you have an ExternalName service type, and the protocol is TCP, rename the port to `<protocol>[-<suffix>]` or `<protocol>` where protocol is `https` or `tls`. To learn more, review
+docs on [explicit protocol selection](/docs/ops/configuration/traffic-management/protocol-selection/#explicit-protocol-selection).
+