serilog-sinks-file | Write Serilog events to files in text and JSON formats | User Interface library

The generally-accepted way to do this is for each app instance to take an exclusive lock on the file prior to writing, and release it when done.

Unfortunately, this requires opening and closing the file a lot, which is VERY slow, and serializes work, which has a cost as the number of machines grows. Serilog doesn't implement this currently, since its one of those features that appears to work in testing, but performs very poorly in production.

Having each app instance write to its own file is a better scheme, but using a network-based log collector/service will be less hassle in the long run.