def update(key, ctx)
      resp = _request_endpoint(ctx)
      if resp && resp.endpoints
        resp.endpoints.each { |e| self[key] = e }
      end
    end
def update(key, ctx)
      resp = _request_endpoint(ctx)
      if resp && resp.endpoints
        resp.endpoints.each { |e| self[key] = e }
      end
    end
update cache with requests (using service endpoint operation)
 to fetch endpoint list (with identifiers when available)
 @param [String] key
 @param [RequestContext] ctx