how to use reactor scheduler in micro-services

Depending on how many cores we have for your micro-services, we may have as low as 4 threads (reactor-http-nio- or reactor-http-epoll-) when it comes to listening and talking to outside. If these threads are blocked in a way we didn't expect, the performance could be worse than traditional synchronised paradigm. Here're a few examples to show how it works when offloading blocking operations to a larger thread pool at different places. Logs happen at doOnSubscribe and doOnSuccess.

no scheduler

[ctor-http-nio-4] Controller     : Received request

[ctor-http-nio-4] ServiceClient  : Getting something

[ctor-http-nio-4] ServiceClient  : Got something in 116ms

[ctor-http-nio-4] Controller     : Processed in 120ms

scheduler on subscribeOn WebClient call to 3rd party

[ctor-http-nio-3] Controller     : Received request

[    scheduler-3] ServiceClient  : Getting something

[ctor-http-nio-4] ServiceClient  : Got something in 116ms

[ctor-http-nio-4] Controller     : Processed in 120ms

scheduler on publishOn WebClient call to 3rd party

[ctor-http-nio-5] Controller     : Received request

[ctor-http-nio-5] ServiceClient  : Getting something

[   scheduler-12] ServiceClient  : Got something in 116ms

[   scheduler-12] Controller     : Processed in 120ms

scheduler on subscribeOn and publishOn WebClient call to 3rd party

[ctor-http-nio-3] Controller     : Received request

[    scheduler-3] ServiceClient  : Getting something

[    scheduler-4] ServiceClient  : Got something in 116ms

[    scheduler-4] Controller     : Processed in 120ms

Bonus cases to make things even tricky.

subscribeOn after doOnSubscribe in controller

[undedElastic-21] Controller     : Received request

[undedElastic-21] ServiceClient  : Getting something

[ctor-http-nio-7] ServiceClient  : Got something in 116ms

[ctor-http-nio-7] Controller     : Processed in 120ms

subscribeOn before doOnSubscribe in controller

[ctor-http-nio-3] Controller     : Received request

[undedElastic-21] ServiceClient  : Getting something

[ctor-http-nio-4] ServiceClient  : Got something in 116ms

[ctor-http-nio-4] Controller     : Processed in 120ms