Werf uses --synchronization=https://synchronization.werf.io as a default synchronization service.
Use "werf synchronization" command to run own synchronization http server. You can also configure werf to use local or kubernetes based synchronization backend.
More info about synchronization in werf: https://werf.io/documentation/internals/stages_and_storage.html#synchronization-locks-and-stages-storage-cache