Unset the backend_id for redirects and gone routes

Backends should only be set for routes with the "backend" handler.
Redirects and gone routes are handled directly in router and are not
proxied. This creates confusion in the data model, as redirect can
currently have a backend (however, its not sent to the backend).

app/models/route.rb

@@ -36,6 +36,7 @@ class Route
   end
 
   before_validation :default_segments_mode
+  before_save :remove_backend_id_for_non_backend_routes
   after_create :cleanup_child_gone_routes
 
   scope :excluding, ->(route) { where(id: { :$ne => route.id }) }
@@ -132,6 +133,10 @@ def validate_backend_id
     end
   end
 
+  def remove_backend_id_for_non_backend_routes
+    self.backend_id = nil unless backend?
+  end
+
   def cleanup_child_gone_routes
     return unless route_type == "prefix"
 

spec/models/route_spec.rb

@@ -215,6 +215,12 @@
         end
       end
 
+      describe "backend_id" do
+        it "is set to nil" do
+          expect(route.backend_id).to be nil
+        end
+      end
+
       context "and segments_mode set to 'ignore'" do
         subject(:route) { FactoryBot.build(:redirect_route, segments_mode: "ignore") }
 
@@ -249,6 +255,20 @@
     end
   end
 
+  describe "changing backend route to redirect route" do
+    it "will clear the backend_id" do
+      route = FactoryBot.create(:backend_route)
+      route.update!(
+        handler: "redirect",
+        redirect_to: "/",
+        redirect_type: "permanent",
+      )
+      route.reload
+
+      expect(route.backend_id).to be nil
+    end
+  end
+
   describe "as_json" do
     subject(:route) { FactoryBot.build(:redirect_route) }