code: public CreateClusterRequest withInstanceGroup(InstanceGroupConfig instanceGroup) {
          if (this.instanceGroups == null) {
              this.instanceGroups = new ArrayList<InstanceGroupConfig>();
          }
          this.instanceGroups.add(instanceGroup);
          return this;
      }
docs: Configure the instance group for the cluster.
  
  @param instanceGroup An InstanceGroupConfig instance.
  @return CreateClusterRequest