A tour of grpc:01 - Basic Theory

gRPC The motive of

In practical projects, there are often more than one way to implement back-end services , And due to technical or business constraints , There are usually many languages   Written Services . In order to communicate with each other, services must use a unified  API  A contract makes an agreement . The agreement shall stipulate that   Set such as : Communication channel , Authentication mechanism 、 Load format 、 Data model and how to handle exceptions .

Of course, we hope that communication can be efficient ( Fast and light ), Because the amount of service information exchange between microservices is usually huge , So communication should be as fast as possible . At the same time, in the case of mobile applications or other situations where the network speed and bandwidth are limited , It is very important to have a lightweight communication protocol to interact with back-end services .

Last , We also want communication to be as simple as possible , For example, we now have a system with thousands of services , We don't want to spend a lot of time writing code that lets services communicate with each other . What we want is some kind of framework , Let the framework help us complete all communication related content , Let developers focus on implementing the core business logic of services .

gRPC  What is it? ?

gRPC  By the first  google  The development of , therefore  gRPC  Medium  g  Often considered to represent  google  It means , In fact  gRPC 1.0 That's what happened when , However, the subsequent versions of  g  Equivalent to a version code  ( for example 1.1  Of  g  representative  good), Can be in  gRPC Version code   To view the . and  gRPC  Now belongs to   Cloud native Foundation (CNCF)  Part of ( Like  k8s). that RPC What does it represent   Why not? ?Remote Procedure Calls It is a form of call , Popular said , It is automatically processed by the underlying framework , Permit   Allow a program on one computer to call a program on another computer . This kind of call is seen by the server , We call... Directly on the client   A method of server code ( Or functions ).

gRPC  How it works ?

client  To have a  stub ( pile ) It provides with Server  Same method ,stub  from  gRpc Automatic generation . Stub  Call... In the background gRPC  The framework communicates with... Through the network  server  Exchange information  . because  stub  The existence of ,client  and  server  Now we only need to care about the implementation of the business   Core logic of  .

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gRPC  Code generation

gRPC How to help us generate  stub Of ?

To give  server  and  client  Generate  stub  We have to start with  Protocol Buffer  In the file  API  contract ( The rules ), package   enclosed   Description of service   And it's   Message payload (payload).

Here's a simple  protoBuf  Format  Protocol Buffer

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In the example file on , Defined Hello  Method ( function ), It uses  HelloRequest  As input , And return a HelloResponse , among  HelloRequest  Contains only one string  name, HelloResponse  There is also a string greet . From an original file like this , By the protocol buffer compiler according to the programming language , Generate server  and  client  Of  stub  Code .

that  gRPC  Why did you use  protocol buffer  As  API Statute ?

1.  It is very easy to read and understand

2.  Let different programming languages , Have a unified description

3.  Use binary format , Same as JSON/XML And other text-based formats ,

smaller 、 Easier to transmit

  and  

Better sequence / Deserialization performance

4.  Provides  client  and  server  Between the   Strong type (Strongly typed) API  contract

5.  Have a lot of  API  Evolution rule , To ensure the API Moving forward / backward   compatible

in fact  gRPC  Not with  Protocol Buffer  Strong binding , We can use  Google Flatbuffers  or  Microsoft Bond Instead of  Protocol Buffer . however  Protocol Buffer  It's a great rule , Because it is supported by many programming languages .

Native implementation :GO、Java、NodeJS

Packaging implementation :C/C++、C#、Objective-C、Python、Ruby、Dart、PHP

Unofficially supported third-party libraries :swift rust typescript ....

gRPC  Why efficient

gRPC  Use  HTTP/2  As its transport protocol , therefore , It inherited  HTTP/2  Some of the great features offered  . for example   Binary system   Format , Compared with other protocols using text-based , Higher performance 、 More robust 、 The transmission is lighter 、 Decoding is more secure , And  protocol buffer  The combination of ; meanwhile  Http/2 Also used  HPACK Compress  HEAD, Reduce overhead and improve performance ;Http/2  Not bad   Multiplexing , This means that the client and the server can pass through a single TPC The connection sends multiple requests and receives multiple responses in parallel ,  This can effectively reduce the delay and improve the utilization efficiency of the network ;Http/2  It also allows the server to push , When a single request is made on the client   Condition , The server can return multiple responses , In most cases , This is good for reducing   client   and   Server side   Round trip delay between is very valuable .

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Http/2  How the bottom layer works

HTTP/2  One  TCP  The connection can withstand multiple two-way flows , Each flow has a unique identifier and carries multiple two-way messages , Every message  ( request / Respond to ) Can be decomposed into multiple binary frames , A frame is the smallest unit that carries different data types , Such as :HEADERS( head )、SETTINGS( Set up )、PRIORITY( priority )、DATA( Data etc. ) etc. .

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Frames on different streams are interleaved on the connection , And will be reassembled when reaching the other end .

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HTTP/2 vs HTTP/1.1

Let's take another look at  HTTP/2  Familiar with  HTTP/1.1  Comparison of

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gRPC  Four types of

One yuan  unary:client Send a request ,server  Reply to a response

Client stream  client streaming: The client sends multiple message flow requests , expect server Reply to only one response

Server stream  server streaming: The client sends only one request , The server replies to multiple message flow responses

Two-way flow  bidirectional streaming: The client and server will send multiple requests and responses in parallel , It is very flexible and   Non blocking , It means , Neither party needs to wait for a response before sending the next message .

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gRPC vs REST

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gRPC  The applicable scenarios of

The service is  gRPC  Where it really works , Because it can achieve low latency and high throughput communication . Because many programming languages provide   Out of the box code generation , So it can also be used in many languages . Point to point communication also uses gRPC Because it's good for both   Provides good support for streams . Last , Because of its lightweight message format , It is also a good choice for the environment with limited network .

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