Lua: Fix ExternalName services without endpoints.

rootfs/etc/nginx/lua/balancer.lua

@@ -106,14 +106,19 @@ local function is_backend_with_external_name(backend)
 end
 
 local function sync_backend(backend)
-  -- We resolve external names before checking if the endpoints are empty
-  -- because the behavior for resolve_external_names when the name was not
-  -- resolved is to return an empty table so we set the balancer to nil below
-  -- see https://github.com/kubernetes/ingress-nginx/pull/10989
+  if not backend.endpoints or #backend.endpoints == 0 then
+    balancers[backend.name] = nil
+    return
+  end
+
   if is_backend_with_external_name(backend) then
     backend = resolve_external_names(backend)
   end
 
+  -- We check if the endpoints are empty after resolving the external names
+  -- because the behavior for resolve_external_names when the name was not
+  -- resolved is to return an empty table so we set the balancer to nil below
+  -- see https://github.com/kubernetes/ingress-nginx/pull/10989
   if not backend.endpoints or #backend.endpoints == 0 then
     balancers[backend.name] = nil
     return

rootfs/etc/nginx/lua/test/balancer_test.lua

@@ -439,6 +439,40 @@ describe("Balancer", function()
       assert.stub(mock_instance.sync).was_called_with(mock_instance, expected_backend)
     end)
 
+    it("sets balancer to nil when service is of type External name and DNS could not resolve", function()
+      backend = {
+        name = "example-com", service = { spec = { ["type"] = "ExternalName" } },
+        endpoints = {
+          { address = "example.com", port = "80", maxFails = 0, failTimeout = 0 }
+        }
+      }
+
+      helpers.mock_resty_dns_query("example.com", {}, "Mock was instructed to return error")
+      local mock_instance = { sync = function(backend) end }
+      setmetatable(mock_instance, implementation)
+      implementation.new = function(self, backend) return mock_instance end
+      local s = spy.on(implementation, "new")
+      assert.has_no.errors(function() balancer.sync_backend(backend) end)
+      assert.spy(s).was_not_called()
+      assert.is_nil(balancer.get_balancer_by_upstream_name(backend.name))
+    end)
+
+    it("sets balancer to nil when service is of type External name and endpoints in nil (omitted by go calling POST /configuration/backends)", function()
+      backend = {
+        name = "example-com", service = { spec = { ["type"] = "ExternalName" } },
+        endpoints = nil
+      }
+
+      helpers.mock_resty_dns_query("example.com", {}, "Mock was instructed to return error")
+      local mock_instance = { sync = function(backend) end }
+      setmetatable(mock_instance, implementation)
+      implementation.new = function(self, backend) return mock_instance end
+      local s = spy.on(implementation, "new")
+      assert.has_no.errors(function() balancer.sync_backend(backend) end)
+      assert.spy(s).was_not_called()
+      assert.is_nil(balancer.get_balancer_by_upstream_name(backend.name))
+    end)
+
     it("wraps IPv6 addresses into square brackets", function()
       local backend = {
         name = "example-com",