The first service syncs data from an external resource to a disc and the second service provides an API for that data. If it is possible to share a volume between the two services ?
Only if you deploy a multi-process Machines or a multi-process Fly app or manage multiple processes with a supervisor: Configuring a reverse proxy for Ruby application - #2 by ignoramous
Otherwise, a single volume cannot be attached to two different VMs (not yet): sharing storage between apps? - #2 by jerome