Is there is a way in NiFi to use a processor such as "PutFile" and have it write to one single file (append data to this file, or over-write the data in this file) - rather than create multiple different files?
Is there another processor I need to use in order to accomplish this?
Currently there is no way to append data to a file but you can overwrite the file using PutFile.
The PutFile processor writes a file to disk using the the attribute "filename" on the FlowFile. So if you put an UpdateAttribute processor before a PutFile that updates all incoming FlowFiles with to same "filename" then the PutFile processor will write them all with the same file name on disk.
To do this with PutFile, make sure you configure processor property "Conflict Resolution Strategy" to "Replace".