code: public void init(String dc_sync_period, String  resources_keep_alive_period, String manager_ip, String manager_port) {
  
          if (registryInitialized)
              throw new RuntimeException("Registry was already initialized");
  
          if (dc_sync_period != null) {
              CONFIG_SYNC_PERIOD = Integer.parseInt(dc_sync_period);
          }
  
          if (resources_keep_alive_period != null) {
              KEEP_ALIVE = Integer.parseInt(resources_keep_alive_period);
          }
  
          // Build metrics
          providedMetrics = buildProvidedMetrics();
  
          // Build the DCAgent
          dcAgent = new DCAgent(new ManagerAPI(manager_ip, Integer.parseInt(manager_port)));
  
          // Add observers of metrics to the DCAgent
          for (Metric metric : providedMetrics) {
              logger.debug("Added metric {} as observer of dcagent",
                      metric.getMonitoredMetric());
              dcAgent.addObserver(metric);
          }
  
          // Build the DCDescriptor
          DCDescriptor dcDescriptor = new DCDescriptor();
  
          dcDescriptor.addMonitoredResources(getProvidedMetrics(), getResources());
          dcDescriptor.addResources(getResources());
  
          dcDescriptor
                  .setConfigSyncPeriod(CONFIG_SYNC_PERIOD != null ? CONFIG_SYNC_PERIOD
                          : DEFAULT_CONFIG_SYNC_PERIOD);
  
          dcDescriptor.setKeepAlive(KEEP_ALIVE != null ? KEEP_ALIVE
                  : (DEFAULT_CONFIG_SYNC_PERIOD + 15));
  
          dcAgent.setDCDescriptor(dcDescriptor);
          registryInitialized = true;
  
      }
docs: This method is used to initialized the collecting of each metric.
  It initializes a DCAgent with the manager_ip and manager_port parameters
  in order to communicate with Tower 4Clouds.
  It then build a DCDescriptor with the list of all the provided metrics
  and the set of monitored resources for each provided metric.
  It then start the DCAgent, which enact the collecting of each metric
  and communicate to Tower 4Clouds the set of monitored resources
  for each provided metric.
  @param dc_sync_period
  @param resources_keep_alive_period
  @param manager_ip
  @param manager_port