Use ErrorPage to render proxy error page

pkg/app/error_page.go

@@ -54,3 +54,11 @@ func (e *ErrorPage) Render(rw http.ResponseWriter, status int, redirectURL strin
 		http.Error(rw, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
 	}
 }
+
+// ProxyErrorHandler is used by the upstream ReverseProxy to render error pages
+// when there are issues with upstream servers.
+// It is expected to always render a bad gateway error.
+func (e *ErrorPage) ProxyErrorHandler(rw http.ResponseWriter, req *http.Request, proxyErr error) {
+	logger.Errorf("Error proxying to upstream server: %v", proxyErr)
+	e.Render(rw, http.StatusBadGateway, "", "Error proxying to upstream server")
+}

pkg/app/error_page_test.go

@@ -1,6 +1,7 @@
 package app
 
 import (
+	"errors"
 	"html/template"
 	"io/ioutil"
 	"net/http/httptest"
@@ -10,19 +11,22 @@ import (
 )
 
 var _ = Describe("Error Page", func() {
+	var errorPage *ErrorPage
+
+	BeforeEach(func() {
+		tmpl, err := template.New("").Parse("{{.Title}} {{.Message}} {{.ProxyPrefix}} {{.StatusCode}} {{.Redirect}} {{.Footer}} {{.Version}}")
+		Expect(err).ToNot(HaveOccurred())
+
+		errorPage = &ErrorPage{
+			Template:    tmpl,
+			ProxyPrefix: "/prefix/",
+			Footer:      "Custom Footer Text",
+			Version:     "v0.0.0-test",
+		}
+	})
 
 	Context("Render", func() {
 		It("Writes the template to the response writer", func() {
-			tmpl, err := template.New("").Parse("{{.Title}} {{.Message}} {{.ProxyPrefix}} {{.StatusCode}} {{.Redirect}} {{.Footer}} {{.Version}}")
-			Expect(err).ToNot(HaveOccurred())
-
-			errorPage := &ErrorPage{
-				Template:    tmpl,
-				ProxyPrefix: "/prefix/",
-				Footer:      "Custom Footer Text",
-				Version:     "v0.0.0-test",
-			}
-
 			recorder := httptest.NewRecorder()
 			errorPage.Render(recorder, 403, "/redirect", "Access Denied")
 
@@ -32,4 +36,15 @@ var _ = Describe("Error Page", func() {
 		})
 	})
 
+	Context("ProxyErrorHandler", func() {
+		It("Writes a bad gateway error the response writer", func() {
+			req := httptest.NewRequest("", "/bad-gateway", nil)
+			recorder := httptest.NewRecorder()
+			errorPage.ProxyErrorHandler(recorder, req, errors.New("some upstream error"))
+
+			body, err := ioutil.ReadAll(recorder.Result().Body)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(string(body)).To(Equal("Bad Gateway Error proxying to upstream server /prefix/ 502  Custom Footer Text v0.0.0-test"))
+		})
+	})
 })

pkg/app/templates.go

@@ -79,6 +79,7 @@ const (
   		</div>
       {{ end }}
 
+      {{ if .Redirect }}
       <hr>
 
       <div class="columns">
@@ -94,6 +95,7 @@ const (
           </form>
         </div>
       </div>
+      {{ end }}
 
     </div>
   </section>