Running a Mono in background while returning a response when using Spring Webflux

AFAIK, using one of the subscribe methods is the only way to really start a job in the background with its own lifecycle (not tied to the returned publisher).

If you were to use one of the operators to combine the job publisher and the response publisher (e.g. zip or merge), then the lifecycle of the job publisher would be tied to the response publisher, which is not what you want for a background job.

One thing you might want to consider is kicking off the background job within the response publisher stream, rather than directly in the method body. e.g. via doOnSubscibe or from an operator upstream of the response.

This would tie the start of the background job to the onSubscribe events of the response publisher, but still allow it to complete in the background.

Also note, that if you want to be able to cancel the background job (e.g. maybe during application shutdown), you'll need to save the Disposable returned from subscribe so you can later call dispose on it. This might be better done from some type of BackgroundJobManager that could keep track of all the jobs running.