Before looking at Dubbo first look at distributed systems
I. What is a distributed system
distributed system is composed of a set of systems communicate over a network, a computer node in order to complete common tasks and coordinate the work of composition. The advent of distributed computing systems in order to complete a single computer can not be completed, storage tasks with cheap, ordinary machines. Its purpose is to use more machines to process more data.
Second, the evolution of
three distributed service architecture
when more and more vertical applications, the inevitable interaction between applications, will be drawn out of the core business, as an independent service, and gradually form a stable service center, the front-end applications more quickly in response to changing market demands. In this case, for improving distributed service framework (RPC) service multiplexing and integration is the key.
Fourth, what is the RPC
RPC [Remote Procedure Call] refers to the Remote Procedure Call, it is an interprocess communication, thinking he is a technique, not the norm. It allows a program to call another address space (typically on another machine sharing network) procedure or function, rather than the programmer explicitly coding details remote calls. That programmer whether to call a local or remote function, essentially calling code written in basically the same.
Five, RPC principle of 
a complete RPC calls and processes (synchronous call)
asynchronous calls
1, the service consumer (client) call to invoke the service;
after 2, clent (client) stub receives the call is responsible for the methods and parameters assembled into message body can be transmitted over the network
3, clent (client) stub find service address, and sends the message to the server
4, decodes the received message sever stub
5, sesrver stub call the local service based on the decoding result;
6, the local service execution and returns to the junction Stub serve
. 7, Server Stub packaged into the return result message sent to the consumer and
8, client stub receiving the message, and decodes
9, the service consumer to obtain a final result
the target frame RPC 2-8 is to encapsulate these steps, these details are transparent to the user, invisible dubbo is to help us do these things
RPC two core modules : communication, serialization.
There are many RPC framework:
Dubbo, GRPC, Thrift, HSF (High Speed Service Framework)
