code: @BetaApi
    public final Operation insertRegionInstanceGroupManager(
        String region, InstanceGroupManager instanceGroupManagerResource) {
  
      InsertRegionInstanceGroupManagerHttpRequest request =
          InsertRegionInstanceGroupManagerHttpRequest.newBuilder()
              .setRegion(region)
              .setInstanceGroupManagerResource(instanceGroupManagerResource)
              .build();
      return insertRegionInstanceGroupManager(request);
    }
docs: Creates a managed instance group using the information that you specify in the request. After
  the group is created, instances in the group are created using the specified instance template.
  This operation is marked as DONE when the group is created even if the instances in the group
  have not yet been created. You must separately verify the status of the individual instances
  with the listmanagedinstances method.
  
  <p>A regional managed instance group can contain up to 2000 instances.
  
  <p>Sample code:
  
  <pre><code>
  try (RegionInstanceGroupManagerClient regionInstanceGroupManagerClient = RegionInstanceGroupManagerClient.create()) {
  ProjectRegionName region = ProjectRegionName.of("[PROJECT]", "[REGION]");
  InstanceGroupManager instanceGroupManagerResource = InstanceGroupManager.newBuilder().build();
  Operation response = regionInstanceGroupManagerClient.insertRegionInstanceGroupManager(region.toString(), instanceGroupManagerResource);
  }
  </code></pre>
  
  @param region Name of the region scoping this request.
  @param instanceGroupManagerResource An Instance Group Manager resource. (== resource_for
  beta.instanceGroupManagers ==) (== resource_for v1.instanceGroupManagers ==) (==
  resource_for beta.regionInstanceGroupManagers ==) (== resource_for
  v1.regionInstanceGroupManagers ==)
  @throws com.google.api.gax.rpc.ApiException if the remote call fails