fix(appsync): allow imported IGraphqlApi resources (#277)

To stay consistent with other parts of the library.

---

_By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license_

Author: Eugene Cheung

API.md

@@ -1,4 +1,4 @@
-import { GraphqlApi } from "@aws-cdk/aws-appsync-alpha";
+import { IGraphqlApi } from "@aws-cdk/aws-appsync-alpha";
 import { DimensionsMap } from "aws-cdk-lib/aws-cloudwatch";
 
 import {
@@ -13,7 +13,7 @@ export interface AppSyncMetricFactoryProps {
   /**
    * the GraphQL API to monitor
    */
-  readonly api: GraphqlApi;
+  readonly api: IGraphqlApi;
   /**
    * whether the TPS should be filled with zeroes
    * @default - true

lib/monitoring/aws-appsync/AppSyncMetricFactory.ts

@@ -1,4 +1,4 @@
-import { GraphqlApi } from "@aws-cdk/aws-appsync-alpha";
+import { GraphqlApi, IGraphqlApi } from "@aws-cdk/aws-appsync-alpha";
 import { Duration, Stack } from "aws-cdk-lib";
 import { Template } from "aws-cdk-lib/assertions";
 
@@ -25,6 +25,29 @@ test("snapshot test: no alarms", () => {
   expect(Template.fromStack(stack)).toMatchSnapshot();
 });
 
+test("snapshot test: no alarms with imported IGraphqlApi", () => {
+  const stack = new Stack();
+
+  const scope = new TestMonitoringScope(stack, "Scope");
+
+  const dummyApi: IGraphqlApi = GraphqlApi.fromGraphqlApiAttributes(
+    scope,
+    "ImportedGraphQlApi",
+    {
+      graphqlApiId: "DummyApiFromElsewhere",
+    }
+  );
+
+  const monitoring = new AppSyncMonitoring(scope, {
+    api: dummyApi,
+    humanReadableName: "Dummy API for testing",
+    alarmFriendlyName: "DummyApi",
+  });
+
+  addMonitoringDashboardsToStack(stack, monitoring);
+  expect(Template.fromStack(stack)).toMatchSnapshot();
+});
+
 test("snapshot test: all alarms", () => {
   const stack = new Stack();