code: @BetaApi
    public final ListInstancesInstanceGroupsPagedResponse listInstancesInstanceGroups(
        String instanceGroup,
        InstanceGroupsListInstancesRequest instanceGroupsListInstancesRequestResource) {
      ListInstancesInstanceGroupsHttpRequest request =
          ListInstancesInstanceGroupsHttpRequest.newBuilder()
              .setInstanceGroup(instanceGroup)
              .setInstanceGroupsListInstancesRequestResource(
                  instanceGroupsListInstancesRequestResource)
              .build();
      return listInstancesInstanceGroups(request);
    }
docs: Lists the instances in the specified instance group.
  
  <p>Sample code:
  
  <pre><code>
  try (InstanceGroupClient instanceGroupClient = InstanceGroupClient.create()) {
  ProjectZoneInstanceGroupName instanceGroup = ProjectZoneInstanceGroupName.of("[PROJECT]", "[ZONE]", "[INSTANCE_GROUP]");
  InstanceGroupsListInstancesRequest instanceGroupsListInstancesRequestResource = InstanceGroupsListInstancesRequest.newBuilder().build();
  for (InstanceWithNamedPorts element : instanceGroupClient.listInstancesInstanceGroups(instanceGroup.toString(), instanceGroupsListInstancesRequestResource).iterateAll()) {
  // doThingsWith(element);
  }
  }
  </code></pre>
  
  @param instanceGroup The name of the instance group from which you want to generate a list of
  included instances.
  @param instanceGroupsListInstancesRequestResource
  @throws com.google.api.gax.rpc.ApiException if the remote call fails