feat(gateway_discovery): allow gateway discovery only in dbless mode

CHANGELOG.md

@@ -109,8 +109,11 @@ Adding a new version? You'll need three changes:
   [#3469](https://github.com/Kong/kubernetes-ingress-controller/pull/3469)
 - Added Gateway discovery using Kong Admin API service configured via `--kong-admin-svc`
   which accepts a namespaced name of a headless service which should have
-  Admin API endpoints exposed under a named port called `admin`.
+  Admin API endpoints exposed under a named port called `admin`. Gateway 
+  discovery is only allowed to run with dbless kong gateways, because it is
+  unnecessary to run gateway discovery with DB-backed kong gateways
   [#3421](https://github.com/Kong/kubernetes-ingress-controller/pull/3421)
+  [#3642](https://github.com/Kong/kubernetes-ingress-controller/pull/3642)
 - Added configurable port names for Gateway discovery through
   `--kong-admin-svc-port-names`. This flag accepts a list of port names that
   Admin API service ports will be matched against.
@@ -149,7 +152,7 @@ Adding a new version? You'll need three changes:
   for the controller and the proxy. This enables the proxy to be scaled independently
   of the controller. The old `all-in-one-dbless.yaml` manifest has been deprecated and 
   renamed to `all-in-one-dbless-legacy.yaml`. It will be removed in a future release.
-  [#3692](https://github.com/Kong/kubernetes-ingress-controller/pull/3629)
+  [#3629](https://github.com/Kong/kubernetes-ingress-controller/pull/3629)
 
 ### Fixed
 

internal/manager/config_validation.go

@@ -113,3 +113,16 @@ func validateClientTLS(clientTLS adminapi.TLSClientConfig) error {
 
 	return nil
 }
+
+// ValidateGatewayDiscovery returns error if dbMode is not configured to db-less mode.
+// gateway discovery is only supported in db-less mode in its initial release:
+// https://github.com/Kong/kubernetes-ingress-controller/issues/3401
+func (c *Config) ValidateGatewayDiscovery(dbMode string) error {
+	if c.KongAdminSvc.IsAbsent() {
+		return nil
+	}
+	if dbMode != "off" && dbMode != "" {
+		return fmt.Errorf("gateway discovery is only supported in dbless mode, not db %s", dbMode)
+	}
+	return nil
+}

internal/manager/config_validation_test.go

@@ -232,3 +232,53 @@ func TestConfigValidate(t *testing.T) {
 		})
 	})
 }
+
+func TestConfigValidateGatewayDiscovery(t *testing.T) {
+	testCases := []struct {
+		name             string
+		gatewayDiscovery bool
+		dbMode           string
+		expectError      bool
+	}{
+		{
+			name:             "gateway discovery disabled should pass in db-less mode",
+			gatewayDiscovery: false,
+			dbMode:           "off",
+			expectError:      false,
+		},
+		{
+			name:             "gateway discovery disabled should pass in db-backed mode",
+			gatewayDiscovery: false,
+			dbMode:           "postgres",
+			expectError:      false,
+		},
+		{
+			name:             "gateway discovery enabled should pass in db-less mode",
+			gatewayDiscovery: true,
+			dbMode:           "",
+			expectError:      false,
+		},
+		{
+			name:             "gateway discovery enabled should not pass in db-backed mode",
+			gatewayDiscovery: true,
+			dbMode:           "postgres",
+			expectError:      true,
+		},
+	}
+
+	for _, tc := range testCases {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			c := &manager.Config{}
+			if tc.gatewayDiscovery {
+				c.KongAdminSvc = mo.Some(types.NamespacedName{Name: "admin-svc", Namespace: "ns"})
+			}
+			err := c.ValidateGatewayDiscovery(tc.dbMode)
+			if !tc.expectError {
+				require.NoError(t, err)
+			} else {
+				require.Error(t, err)
+			}
+		})
+	}
+}

internal/manager/run.go

@@ -70,6 +70,12 @@ func Run(ctx context.Context, c *Config, diagnostic util.ConfigDumpDiagnostic, d
 	if err != nil {
 		return fmt.Errorf("could not validate Kong admin root(s) configuration: %w", err)
 	}
+
+	err = c.ValidateGatewayDiscovery(dbMode)
+	if err != nil {
+		return err
+	}
+
 	semV := semver.Version{Major: v.Major(), Minor: v.Minor(), Patch: v.Patch()}
 	versions.SetKongVersion(semV)