AsyncLocalStorage and streams

[the-spyke]

I have an Express application using AsyncLocalStorage to create a request context and a Winston logger with context format. The format is just adding data like requestId from the async context to the log message.

Sometimes some of the logs don't have that requestId and it looks like this happens the most during peak load. As Winston is based on streams, is it possible that logs get buffered and flushed by some timer or OS callback, so format (next transform stream in the chain) could not find the right context anymore?