Where is the business logic written using the microservice framework istio,?

the Nuggets just read two istio articles, https://github.com/istio/istio

I don"t understand much. Question:
where should the business logic be written when using this micro-service framework? Do you want to write in java?

Mar.04,2021

istio is a proxy behind your program, non-intrusive, and does not need to be changed to existing code. For more information, please see istio architecture

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