Alerting: Validate extra configuration with PostableApiAlertingConfig (#108706)

pkg/services/ngalert/api/tooling/definitions/alertmanager.go

@@ -745,12 +745,14 @@ func (c ExtraConfiguration) Validate() error {
 		}
 	}
 
-	// Alertmanager configuration is validated during YAML unmarshalling.
-	am := config.Config{}
-	err := yaml.Unmarshal([]byte(c.AlertmanagerConfig), &am)
+	cfg, err := c.GetAlertmanagerConfig()
 	if err != nil {
 		return errInvalidExtraConfiguration(fmt.Errorf("failed to parse alertmanager config: %w", err))
 	}
+	err = cfg.Validate()
+	if err != nil {
+		return errInvalidExtraConfiguration(fmt.Errorf("invalid alertmanager config: %w", err))
+	}
 
 	return nil
 }

pkg/services/ngalert/api/tooling/definitions/alertmanager_test.go

@@ -403,3 +403,93 @@ func TestPostableUserConfig_GetMergedTemplateDefinitions(t *testing.T) {
 		})
 	}
 }
+
+func TestExtraConfiguration_Validate(t *testing.T) {
+	testCases := []struct {
+		name          string
+		config        ExtraConfiguration
+		expectedError string
+	}{
+		{
+			name: "valid configuration",
+			config: ExtraConfiguration{
+				Identifier:    "test-config",
+				MergeMatchers: config.Matchers{{Type: labels.MatchEqual, Name: "env", Value: "prod"}},
+				AlertmanagerConfig: `route:
+  receiver: default
+receivers:
+  - name: default`,
+			},
+		},
+		{
+			name: "empty identifier",
+			config: ExtraConfiguration{
+				Identifier:         "",
+				MergeMatchers:      config.Matchers{{Type: labels.MatchEqual, Name: "env", Value: "prod"}},
+				AlertmanagerConfig: `route: {receiver: default}`,
+			},
+			expectedError: "identifier is required",
+		},
+		{
+			name: "invalid matcher type",
+			config: ExtraConfiguration{
+				Identifier:    "test-config",
+				MergeMatchers: config.Matchers{{Type: labels.MatchNotEqual, Name: "env", Value: "prod"}},
+				AlertmanagerConfig: `route:
+  receiver: default
+receivers:
+  - name: default`,
+			},
+			expectedError: "only matchers with type equal are supported",
+		},
+		{
+			name: "invalid YAML alertmanager config",
+			config: ExtraConfiguration{
+				Identifier:         "test-config",
+				MergeMatchers:      config.Matchers{{Type: labels.MatchEqual, Name: "env", Value: "prod"}},
+				AlertmanagerConfig: `invalid: yaml: content: [`,
+			},
+			expectedError: "failed to parse alertmanager config",
+		},
+		{
+			name: "missing route in alertmanager config",
+			config: ExtraConfiguration{
+				Identifier:    "test-config",
+				MergeMatchers: config.Matchers{{Type: labels.MatchEqual, Name: "env", Value: "prod"}},
+				AlertmanagerConfig: `receivers:
+  - name: default`,
+			},
+			expectedError: "no routes provided",
+		},
+		{
+			name: "missing receivers in alertmanager config",
+			config: ExtraConfiguration{
+				Identifier:    "test-config",
+				MergeMatchers: config.Matchers{{Type: labels.MatchEqual, Name: "env", Value: "prod"}},
+				AlertmanagerConfig: `route:
+  receiver: default`,
+			},
+			expectedError: "undefined receiver",
+		},
+		{
+			name: "empty alertmanager config",
+			config: ExtraConfiguration{
+				Identifier:         "test-config",
+				MergeMatchers:      config.Matchers{{Type: labels.MatchEqual, Name: "env", Value: "prod"}},
+				AlertmanagerConfig: "",
+			},
+			expectedError: "failed to parse alertmanager config",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			err := tc.config.Validate()
+			if tc.expectedError == "" {
+				require.NoError(t, err)
+			} else {
+				require.ErrorContains(t, err, tc.expectedError)
+			}
+		})
+	}
+}