code: public Observable<ServerDnsAliasInner> createOrUpdateAsync(String resourceGroupName, String serverName, String dnsAliasName) {
          return createOrUpdateWithServiceResponseAsync(resourceGroupName, serverName, dnsAliasName).map(new Func1<ServiceResponse<ServerDnsAliasInner>, ServerDnsAliasInner>() {
              @Override
              public ServerDnsAliasInner call(ServiceResponse<ServerDnsAliasInner> response) {
                  return response.body();
              }
          });
      }
docs: Creates a server dns alias.
  
  @param resourceGroupName The name of the resource group that contains the resource. You can obtain this value from the Azure Resource Manager API or the portal.
  @param serverName The name of the server that the alias is pointing to.
  @param dnsAliasName The name of the server DNS alias.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable for the request