fix: move resource detection to the first export to avoid slow start (#2450)

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:
- [ ] Make sure to open an issue as a [bug/issue](https://togithub.com/googleapis/java-bigtable/issues/new/choose) before writing your code!  That way we can discuss the change, evaluate designs, and agree on the general idea
- [ ] Ensure the tests and linter pass
- [ ] Code coverage does not decrease (if any source code was changed)
- [ ] Appropriate docs were updated (if necessary)
- [ ] Rollback plan is reviewed and LGTMed
- [ ] All new data plane features have a completed end to end testing plan

Fixes #<issue_number_goes_here> ☕️

If you write sample code, please follow the [samples format](
https://togithub.com/GoogleCloudPlatform/java-docs-samples/blob/main/SAMPLE_FORMAT.md).

Author: mutianf

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/stub/metrics/BigtableCloudMonitoringExporter.java

@@ -40,6 +40,8 @@
 import com.google.cloud.monitoring.v3.MetricServiceClient;
 import com.google.cloud.monitoring.v3.MetricServiceSettings;
 import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Supplier;
+import com.google.common.base.Suppliers;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Iterables;
@@ -96,8 +98,9 @@ public final class BigtableCloudMonitoringExporter implements MetricExporter {
 
   private final String taskId;
 
-  // The resource the client application is running on
-  private final MonitoredResource applicationResource;
+  // Application resource is initialized on the first export, which runs on a background thread
+  // to avoid slowness when starting the client.
+  private final Supplier<MonitoredResource> applicationResource;
 
   private final AtomicBoolean isShutdown = new AtomicBoolean(false);
 
@@ -148,28 +151,15 @@ public static BigtableCloudMonitoringExporter create(
     // it as not retried for now.
     settingsBuilder.createServiceTimeSeriesSettings().setSimpleTimeoutNoRetriesDuration(timeout);
 
-    // Detect the resource that the client application is running on. For example,
-    // this could be a GCE instance or a GKE pod. Currently, we only support GCE instance and
-    // GKE pod. This method will return null for everything else.
-    MonitoredResource applicationResource = null;
-    try {
-      applicationResource = BigtableExporterUtils.detectResource();
-    } catch (Exception e) {
-      logger.log(
-          Level.WARNING,
-          "Failed to detect resource, will skip exporting application level metrics ",
-          e);
-    }
-
     return new BigtableCloudMonitoringExporter(
         MetricServiceClient.create(settingsBuilder.build()),
-        applicationResource,
+        Suppliers.memoize(BigtableExporterUtils::detectResourceSafe),
         BigtableExporterUtils.getDefaultTaskValue());
   }
 
   @VisibleForTesting
   BigtableCloudMonitoringExporter(
-      MetricServiceClient client, @Nullable MonitoredResource applicationResource, String taskId) {
+      MetricServiceClient client, Supplier<MonitoredResource> applicationResource, String taskId) {
     this.client = client;
     this.taskId = taskId;
     this.applicationResource = applicationResource;
@@ -257,7 +247,7 @@ public void onSuccess(List<Empty> emptyList) {
   /** Export metrics associated with the resource the Application is running on. */
   private CompletableResultCode exportApplicationResourceMetrics(
       Collection<MetricData> collection) {
-    if (applicationResource == null) {
+    if (applicationResource.get() == null) {
       return CompletableResultCode.ofSuccess();
     }
 
@@ -276,7 +266,7 @@ private CompletableResultCode exportApplicationResourceMetrics(
     try {
       timeSeries =
           BigtableExporterUtils.convertToApplicationResourceTimeSeries(
-              metricData, taskId, applicationResource);
+              metricData, taskId, applicationResource.get());
     } catch (Throwable e) {
       logger.log(
           Level.WARNING,
@@ -291,7 +281,8 @@ private CompletableResultCode exportApplicationResourceMetrics(
     CompletableResultCode exportCode = new CompletableResultCode();
     try {
       ProjectName projectName =
-          ProjectName.of(applicationResource.getLabelsOrThrow(APPLICATION_RESOURCE_PROJECT_ID));
+          ProjectName.of(
+              applicationResource.get().getLabelsOrThrow(APPLICATION_RESOURCE_PROJECT_ID));
 
       gceOrGkeFuture = exportTimeSeries(projectName, timeSeries);
 

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/stub/metrics/BigtableExporterUtils.java

@@ -156,7 +156,20 @@ static List<TimeSeries> convertToApplicationResourceTimeSeries(
   }
 
   @Nullable
-  static MonitoredResource detectResource() {
+  static MonitoredResource detectResourceSafe() {
+    try {
+      return detectResource();
+    } catch (Exception e) {
+      logger.log(
+          Level.WARNING,
+          "Failed to detect resource, will skip exporting application level metrics ",
+          e);
+      return null;
+    }
+  }
+
+  @Nullable
+  private static MonitoredResource detectResource() {
     GCPPlatformDetector detector = GCPPlatformDetector.DEFAULT_INSTANCE;
     DetectedPlatform detectedPlatform = detector.detectPlatform();
     MonitoredResource monitoredResource = null;

google-cloud-bigtable/src/test/java/com/google/cloud/bigtable/data/v2/stub/metrics/BigtableCloudMonitoringExporterTest.java

@@ -37,6 +37,7 @@
 import com.google.api.gax.rpc.UnaryCallable;
 import com.google.cloud.monitoring.v3.MetricServiceClient;
 import com.google.cloud.monitoring.v3.stub.MetricServiceStub;
+import com.google.common.base.Suppliers;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.monitoring.v3.CreateTimeSeriesRequest;
@@ -95,7 +96,7 @@ public void setUp() {
 
     exporter =
         new BigtableCloudMonitoringExporter(
-            fakeMetricServiceClient, /* applicationResource= */ null, taskId);
+            fakeMetricServiceClient, /* applicationResource= */ Suppliers.ofInstance(null), taskId);
 
     attributes =
         Attributes.builder()
@@ -308,11 +309,12 @@ public void testTimeSeriesForMetricWithGceOrGkeResource() {
     BigtableCloudMonitoringExporter exporter =
         new BigtableCloudMonitoringExporter(
             fakeMetricServiceClient,
-            MonitoredResource.newBuilder()
-                .setType("gce-instance")
-                .putLabels("some-gce-key", "some-gce-value")
-                .putLabels("project_id", gceProjectId)
-                .build(),
+            Suppliers.ofInstance(
+                MonitoredResource.newBuilder()
+                    .setType("gce-instance")
+                    .putLabels("some-gce-key", "some-gce-value")
+                    .putLabels("project_id", gceProjectId)
+                    .build()),
             taskId);
     ArgumentCaptor<CreateTimeSeriesRequest> argumentCaptor =
         ArgumentCaptor.forClass(CreateTimeSeriesRequest.class);