Understanding RPC and rest

What is? RPC？
Remote procedure call , Just two services A、B, An application is deployed in A Server , Want to call B Functions provided by the application on the server / Method , Because it's not in a memory space , Can't call directly , We need to express the semantics and data of the call through the network .
RPC Will hide the underlying communication details （ It doesn't need to be dealt with directly Socket Communication or Http Communications ）
RPC It's a request response model . Client initiates request , Server returns response （ Be similar to Http How it works ）
that ：

• First , To solve the problem of communication , Mainly through the establishment between the client and the server TCP Connect , All the data exchanged by the remote procedure call is transferred in this connection . Connections can be on-demand , It will be broken after the call , It can also be a long connection , Multiple remote procedure calls share the same connection .
• second , To solve the problem of addressing , in other words ,A How does the application on the server tell the underlying RPC frame , How to connect to B The server （ Such as mainframe or IP Address ） And specific ports , What is the name of the method , This completes the call . For example, based on Web Service protocol stack RPC, We need to provide a endpoint
  URI, Or from UDDI Find... On the service . If it is RMI Call it , I need one more RMI Registry To register the service address .
• Third , When A When an application on the server initiates a remote procedure call , The parameters of the method need to pass the underlying network protocol such as TCP Pass on to B The server , Because the network protocol is based on binary , The values of parameters in memory should be sequenced into binary form , That is serialization （Serialize） Or group （marshal）, Send serialized binaries to by addressing and transferring B The server .
• Fourth ,B After the server receives the request , You need to deserialize the parameters （ The reverse operation of serialization ）, Revert to in memory expression , Then find the corresponding method （ Part of addressing ） Make a local call , And then you get the return value .
• The fifth , The return value is also sent back to the server A Application on , It also needs to be sent by serialization , The server A When received , Deserialization , Revert to in memory expression , hand A Applications on the server .

altogether 9 Step ：

• 1） Service consumer （client） The invocation invokes the service as a local invocation ;
• 2）client stub Responsible for receiving the call 、 The parameters are assembled into a message body capable of network transmission ;
• 3）client stub Find the service address , And send the message to the server ;
• 4）server stub Decode the message upon receipt ;
• 5）server stub The local service is invoked based on the decoding results ;
• 6） The local service executes and returns the result to server stub;
• 7）server stub The returned result is packaged into a message and sent to the consumer ;
• 8）client stub Message received , And decode it ;
• 9） Service consumers get the end result .

quote ：https://www.zhihu.com/question/25536695/answer/109977506

What is? REST？
REST It's an architectural style , A set of architectural constraints and principles . Applications or designs that meet these constraints and principles are RESTful.REST Norms treat everything as a resource , Everything on the Internet is full of resources .
REST No new technology has been created , Components or services , Just use Web The existing characteristics and capabilities of . Can pass through completely HTTP Protocol implementation , Use HTTP Protocol deals with data communication .REST The operation of architecture on resources includes obtaining 、 establish 、 The operations of modifying and deleting resources are exactly the same HTTP Provided by agreement GET、POST、PUT and DELETE Method .

REST and RPC Comparison ：
RPC To realize some pain points of inter service invocation ：

• 1.RPC The way the service provider and the caller interface depend on each other is too strong , It will lead to the complexity of coding , and REST Interface comparison RPC More lightweight , The dependency between the service provider and the caller depends only on a contract , There is no strong code level dependency .
• 2.RPC Services are platform sensitive , It is difficult to simply reuse ：REST Cross platform , The caller of any language can implement... According to the interface definition .

Unified interface
RESTful Architectural style rules , Meta operation of data , namely CRUD(create, read, update and delete, That is, the addition, deletion, search and modification of data ) operation , Corresponding to HTTP Method ：GET Used to obtain resources ,POST Used to create a new resource （ Can also be used to update resources ）,PUT Used to update resources ,DELETE Used to delete resources , In this way, the interface of data operation is unified , Only through HTTP Method , You can complete all the work of adding, deleting, checking and modifying data .
namely ：

• GET（SELECT）： Get resources from the server （ One or more ）.
• POST（CREATE）： Create a new resource on the server .
• PUT（UPDATE）： Update resources on the server （ The client provides complete resource data ）.
• PATCH（UPDATE）： Update resources on the server （ The client provides the resource data that needs to be modified ）.
• DELETE（DELETE）： Remove resources from server .

URI
You can use a URI（ Uniform resource locator ） Point to resources , each URI All correspond to a specific resource . To get this resource , Visit its URI Can , therefore URI It becomes the address or ID of each resource .
General , At least one for each resource URI With the corresponding , Most typical URI namely URL
No state
The so-called stateless , That is, all resources , Both can pass URI location , And this positioning has nothing to do with other resources , Nor will it change because of changes in other resources . The difference between stateful and stateless , Take a simple example to illustrate . For example, query the salary of employees , If you need to log in to the system to query salary , Enter the salary query page , After performing the relevant operations , How much do you get paid , Then there is a state , Because every step of querying salary depends on the previous step , As long as the pre operation is not successful , Subsequent operations cannot be performed ; If you enter a url You can get the salary of the designated employee , Then this situation is stateless , Because getting paid doesn't depend on other resources or status , And in this case , Employee pay is a resource , By a url With the corresponding , Can pass HTTP Medium GET Method to get resources , This is typical RESTful style .

RPC And RESTful The difference is shown in the following two figures ：

Dubbo Adopted RPC Service call for ,SpringCloud Adopted REST.


How to choose micro service communication
We still need to consider the actual situation , Personal understanding

• There are strict requirements for performance ：RPC
• Consider the cost of learning , The difficulty of team members and the cost of development efficiency ：REST
• Demand for opening up ,rpc Need further conversion , and rest It can be directly opened to the outside world ：REST
• Code coupling requires loose coupling ：REST
• Integration with other frameworks is less difficult , The microservice framework basically supports rest：REST
• Asynchronous requirements ,rest Additional means of implementation are required , Such as through middleware ：RPC

Suggest ：
REST It's very convenient to call and test ,RPC It seems a little cumbersome , however RPC There is no doubt about the efficiency of , Therefore, it is recommended to use... For internal calls between multiple systems RPC. Services provided to the outside world ,Rest More appropriate .