code: public static synchronized ElasticsearchClient getSingleton() {
          if (singleton == null) {
              singleton = new ElasticsearchClient();
              try {
                  singleton.init();
              } catch (Exception e) {
                  log.log(Level.SEVERE, "Failed to initialise Elasticsearch client", e);
              }
          }
          return singleton;
      }
docs: This method explicit instantiates the singleton. For use outside a CDI environment.
  
  @return The singleton