FTS Service Evolution and LHC Run-3 Operations

The File Transfer Service (FTS) is a software system responsible for queuing, scheduling, dispatching and retrying file transfer requests, it is used by three of the LHC experiments, namely ATLAS, CMS and LHCb, as well as non LHC experiments including AMS, Dune and NA62. FTS is critical to the success of many experiments and the service must remain available and performant during the entire LHC Run-3. Experiments use FTS to manage the transfer of their physics files all over the World or more specifically all over the Worldwide LHC Computing Grid (WLCG). Since the start of LHC Run-3 (from 5th July 2022 to 31st August 2023), FTS has managed the successful transfer of approximately 1.2 billion files totalling 1.83 Exabytes of data.This paper describes how the FTS team has evolved the software and the deployment in order to cope with changes in implementation technologies, increase the efficiency of service, streamline its operations, and to meet the ever changing needs of its user community. We report about the software migration from Python 2 to Python 3, the move from the Pylons web development framework towards Flask and the new database deployment strategy to separate the handling of the critical operations from the long duration monitoring queries. In addition, during 2022 a new HTTP based protocol has been finalised that can now be used between FTS and compatible WLCG tape storage endpoints.