code: def _find_usage_nodes(self):
          
          nodes = 0
          paginator = self.conn.get_paginator('describe_cache_clusters')
          for page in paginator.paginate(ShowCacheNodeInfo=True):
              for cluster in page['CacheClusters']:
                  try:
                      num_nodes = len(cluster['CacheNodes'])
                  except (IndexError, TypeError, KeyError):
                      # sometimes CacheNodes is None...
                      logger.debug(
                          "Cache Cluster '%s' returned dict with CacheNodes "
                          "None", cluster['CacheClusterId'])
                      num_nodes = cluster['NumCacheNodes']
                  nodes += num_nodes
                  if cluster['Engine'] == 'memcached':
                      self.limits['Nodes per Cluster']._add_current_usage(
                          num_nodes,
                          aws_type='AWS::ElastiCache::CacheCluster',
                          resource_id=cluster['CacheClusterId'],
                      )
  
          self.limits['Nodes']._add_current_usage(
              nodes,
              aws_type='AWS::ElastiCache::CacheNode'
          )
docs: find usage for cache nodes