[lmm]

I wouldn't call it a "debugger", but plenty of people run an instrumentation agent like New Relic or AppDynamics that records tracing information on their production web services with little or even zero modification to their application code.

[conradludgate]

> zero modifications

Highly depends on the language or framework. I used to use NewRelic APM with Go and it required additional code to instrument.

All languages I have used in production require manual instrumentation. For that tracing and logging both work well in my experience.

[lmm]

> I used to use NewRelic APM with Go and it required additional code to instrument.

I'm not surprised, Go's runtime is pretty limited. But for e.g. Java if you're using a well-known/"standard" framework you can just flick the switch and it'll give you a lot of good useful information - additional manual instrumentation usually helps, but the level of instrumentation without it is useful.