Split documentation

docs/user-guide/custom-errors.md

@@ -0,0 +1,18 @@
+# Custom errors
+
+In case of an error in a request the body of the response is obtained from the `default backend`.
+Each request to the default backend includes two headers:
+
+- `X-Code` indicates the HTTP code to be returned to the client.
+- `X-Format` the value of the `Accept` header.
+
+**Important:** the custom backend must return the correct HTTP status code to be returned. NGINX do not changes the reponse from the custom default backend.
+
+Using this two headers is possible to use a custom backend service like [this one](https://github.com/kubernetes/ingress-nginx/tree/master/examples/customization/custom-errors/nginx) that inspect each request and returns a custom error page with the format expected by the client. Please check the example [custom-errors](examples/customization/custom-errors/README.md)
+
+NGINX sends aditional headers that can be used to build custom response:
+
+- X-Original-URI
+- X-Namespace
+- X-Ingress-Name
+- X-Service-Name