The communication in Monolithic applications are interprocess communication.

▪ Working on single process that invoke one to another by

using method calls. Create class and call the method inside

of target module. All running the same process.

▪ The biggest challenge when moving to microservicesbased application is changing the communication

mechanism.

▪ Microservices are distributed and microservices

communicate with each other by inter-service

communication on network level.

▪ Services must interact using an inter-service

communication protocols like HTTP, gRPC or message

brokers AMQP protocol

https://learn.microsoft.com/en-us/dotnet/architecture/microservices/architect-microservice-container-applications/communication-in-microservice-architecture