Introduction to Eureka

Eureka brief introduction

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Preface

“Eureka From ancient Greek words , Meaning for " Found out ”, In the field of software ,Eureka yes Netflix An open source service registration and discovery component of online film company , And others Netflix The company's service components （ For example, load balancer , Fuse , Gateway, etc. ） Together , By SpringCloud Community integration as Spring Cloud Netflix modular

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One 、Eureka brief introduction

and Zookeeper similar ,Eureka Is a component of service registration and discovery , At first, it was mainly used in Amazon's cloud computing service platform AWS,Eureka It is divided into Eureka Server and Eureka Client,Eureka Server by Eureka Service registry ,Eureka Client by Eureka client .
Service registration means ： When each microservice starts , Register your network address and other information to Eureka, The service provider puts its own information, such as the service name , service ip Inform the service registry .

Two 、 Some of the concepts

• Register — Service registration

       When Eureka Client  towards Eureka server  Registration time ,Eureka Client 
       Provide its own metadata , such as  ip  Address 、 port 、 Of health indicators URL, Home page     
       Address information .
  

• Renew — Renewal of service
  Eureka Client By default , Every time 30s Send a heartbeat renewal , Inform... Through service renewal Eureka Server The Eureka Client Still available , Under normal circumstances , If Eureka Server 90 s I didn't receive Eureka Client The heart of ,Eureka Server Will Eureka Client Remove... From the registration list , Be careful : It is recommended on the official website that you do not change the interval between service renewals

• Fetch Registries — Get service registration list information
  Eureka Client from Eureka Server Get service registry information , And cache it locally .Eureka Client Will use the service registration list information to find other service information , To make a remote call , The registration list information timing （ every other 30s） Updated once , The registration list information returned each time may be related to Eureka Client Cache information is different ,Eureka Client Will retrieve the information of the whole registry .Eureka Server Cache all service registry information , And compressed .Eureka Server and Eureka Client have access to json and xml Data format for communication , Default ,Eureka Client Use JSON To get the information of the registration list

• Cancel — Service offline
  Eureka Client When the program is closed, you can turn to Eureka Server Send offline request , After sending the request , The instance information of this client will be from Eureka Server Delete... From the service registration list . The offline request will not be completed automatically , You need to call the following code when the program is closed ：
  DiscoveryManager.getInstance().shudownComponent();

• Eviction — Service to eliminate
  By default ,Eureka Client continuity 90s Not to Eureka Server Send service renewal （ heartbeat ） when ,Eureka Server The service will be deleted from the service list , That is, service elimination

3、 ... and 、Eureka Self protection

When there is a new Eureka Server When it appears , He tried from the neighboring Peer The node obtains the registration information of all service instances . If from adjacent Peer Node failed to get information ,Eureka Server Will try something else Peer node . If Eureka Server Can successfully obtain all service instance information . Then set the service renewal threshold according to the configuration information . At any time , If Eureka Server Service renewal received is less than the percentage configured for this value （ Default 15 Less than in minutes 85%）, Then the server starts the self-protection mode , That is, the information in the registration list is not deleted .
The advantage of doing so is , If Eureka Server Caused by their own network problems Eureka Client Can't renew ,Eureka Client Registration list information is no longer deleted , That is to say Eureka Client It can also be consumed by other services .