In the last one First time to know SpringCloud Microservices in , We briefly talk about service providers and consumers , When there are more services , There will be confusion between dependence and management , And the need to expose their address , To solve these problems , We learn Eureka Registry Center .

  Eureka Registry Center

1. know Eureka

First of all, let's solve the first problem , Management of services .

Problem analysis

In the case just now ,user-service External services , Need to expose your address . and consumer( caller ) The address of the service provider needs to be recorded . Address change in the future , It needs to be updated in time . It doesn't feel like much when there's less service , But in today's increasingly complex Internet Environment , One project will definitely be divided into more than ten , Even dozens of microservices . At this time, if the administrator still manages the address , Not only development difficulties , Future testing 、 It will be very troublesome to launch , This is related to DevOps Our thoughts are contrary .

online car-hailing

It's like Before the appearance of online car Hailing , When people go out for a taxi, they can only call a taxi . Some private cars want to rent but are not qualified , It's called the black car . And a lot of people want a car appointment , But there are too few taxis , inconvenient . There are many private cars, but they dare not stop them , And cars all over the street , Who knows which one is willing to carry people . One wants , One is willing to give , It's just a lack of introducers , Lack of management .

At this time, Didi, such as the network car Hailing platform, appears , All private cars that want to carry passengers are registered in Didi , Record your model ( Service type ), Identity information ( Contact information ). Private cars providing services in this way , It can be found in Didi , Be clear at a glance .

People who want to call at this time , Just open it APP, Enter your destination , Choice of vehicle type ( Service type ), Didi automatically arranges a car to meet your needs , Serve you , perfect !

Eureka What do you do ?

Eureka It's like dripping , Responsible for managing the 、 Record service provider information . Service callers don't need to find their own services , It's about telling your needs Eureka, then Eureka Will tell you the services that meet your needs .

meanwhile , Service provider and Eureka Through between “ heartbeat ” Mechanism for monitoring , When a service provider has a problem ,Eureka It will naturally be removed from the list of services .

This enables automatic registration of services 、 Find out 、 Condition monitoring .

2. Schematic diagram

Basic framework :

  • Eureka: Service registry ( It can be a cluster ), Expose your address

  • Provider : Starts to Eureka Register your own information ( Address , What services do you provide? )

  • consumer : towards Eureka A subscription service ,Eureka A list of all provider addresses for the corresponding service will be sent to the consumer , And regularly updated

  • heartbeat ( The contract ): Provider passes on a regular basis http Way to Eureka Refresh your status

3. Introductory cases

3.1. To write EurekaServer

Next we create a project , Start a EurekaServer:

Still used spring Fast build tools provided :

Selective dependency :

complete Pom file :

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="" xmlns:xsi=""


<description>Demo project for Spring Boot</description>

<relativePath/> <!-- lookup parent from repository -->

<!-- SpringCloud edition , Is the latest F series -->

<!-- Eureka Server side -->

<!-- SpringCloud rely on , Make sure to put dependencyManagement in , As a management version -->


<name>Spring Milestones</name>

Write the startup class :

@EnableEurekaServer // Declare that this application is a EurekaServer
public class EurekaDemoApplication {

public static void main(String[] args) {, args);

Write the configuration :

port: 10086 # port
name: eureka-server # apply name , Will be in Eureka It shows that
register-with-eureka: false # Whether to register your own information to EurekaServer, The default is true
fetch-registry: false # Whether to pull information of other services , The default is true
service-url: # EurekaServer The address of , Now it's your address , If it's a cluster , Need to add others Server The address of .

Start the service , And access :

3.2. take user-service Sign up to Eureka

Registration service , Is to add Eureka Client dependency for , The client code will automatically register the service to the EurekaServer in .

We are user-service-demo Add Eureka Client dependency :

To add SpringCloud rely on :

Open on startup class Eureka Client function

By adding @EnableDiscoveryClient To open Eureka Client function

@EnableDiscoveryClient // Turn on EurekaClient function
public class UserServiceDemoApplication {
    public static void main(String[] args) {, args);

Write the configuration

Be careful :

  • Here we add Property to specify the application name , It will be used in the future id Use .

  • Don't have to specify register-with-eureka and fetch-registry, Because the default is true

Restart project , visit Eureka Monitoring the page see

We found that user-service The service has been registered successfully

3.3. Consumers from Eureka Access to services

Let's modify it consumer-demo, Try from EurekaServer Access to services .

The approach is similar to that of consumers , Just add to the project EurekaClient rely on , You can get the information through the service name !

1) Add dependency :

To add SpringCloud rely on :

And then there was Eureka client :

<!-- Eureka client -->

2) Open in startup class Eureka client

@EnableDiscoveryClient // Turn on Eureka client
public class UserConsumerDemoApplication {
    public RestTemplate restTemplate() {
    return new RestTemplate(new OkHttp3ClientHttpRequestFactory());
  public static void main(String[] args) {, args);

3) Modify the configuration :

4) Modify the code , use DiscoveryClient Class method , According to service name , Get service instance :

public class UserService {

    private RestTemplate restTemplate;

    private DiscoveryClient discoveryClient;// Eureka client , Service instance information can be obtained

public List<User> queryUserByIds(List<Long> ids) {
    List<User> users = new ArrayList<>();
    // String baseUrl = "http://localhost:8081/user/";
    // According to service name , Get service instance
    List<ServiceInstance> instances = discoveryClient.getInstances("user-service");
    // Because there's only one UserService, So we're directly get(0) obtain
    ServiceInstance instance = instances.get(0);
    // obtain ip And port information
    String baseUrl = "http://"+instance.getHost() + ":" + instance.getPort()+"/user/";
    ids.forEach(id -> {
    // We test multiple queries ,
    users.add(this.restTemplate.getForObject(baseUrl + id, User.class));
    // Each interval 500 millisecond
    try {
    } catch (InterruptedException e) {
  return users;

5)Debug Tracking operation :

Generated URL:

Access to the results :

4.Eureka Detailed explanation

Let's talk about it in detail Eureka Principle and configuration of .

4.1. Infrastructure

Eureka Three core roles in architecture :

  • Service registry

    Eureka Server application of , Service registration and discovery , That's what we just built eureka-demo

  • Service providers

    Applications providing services , It can be SpringBoot application , It can also be implemented by any other technology , As long as the external supply is Rest Style service . In this case, we implemented user-service-demo

  • Serving consumers

    Consumer app gets service list from registry , So as to know the information of each service party , Know where to call the service provider . In this case, we implemented consumer-demo

4.2. Highly available Eureka Server

Eureka Server A registry of services , In the case just now , We only have one EurekaServer, in fact EurekaServer It can also be a cluster , Form highly available Eureka center .

Service synchronization

Multiple Eureka Server They also register with each other as services , When the service provider registers with Eureka Server When a node in the cluster , This node synchronizes the service information to each node in the cluster , So as to achieve Data synchronization . therefore , No matter the client accesses Eureka Server Any node in the cluster , Can get complete service list information .

Build high availability by hand EurekaServer

Let's suppose we build two EurekaServer The cluster of , Ports are :10086 and 10087

1) We changed the original EurekaServer To configure :

So called high availability registry , It's just a way of EurekaServer Register yourself as a service , So many EurekaServer We can find each other , To form a cluster . So we made the following changes :

  • Deleted register-with-eureka=false and fetch-registry=false Two configurations . Because the default is true, So you can register yourself in the registry .

  • hold service-url The value of has been changed to another EurekaServer The address of , Not myself

2) The other configuration is just the opposite :

Be careful :idea An app in cannot be started twice , We need to reconfigure an initiator :

Then start .

3) Start the test :

4) Client registration service to cluster

because EurekaServer More than one , So when you sign up for services ,service-url Parameters need to change :

4.3. Service providers

The service provider should EurekaServer Registration service , And complete service renewal and other work .

Service registration

The service provider at startup , The :eureka.client.register-with-erueka=true Is the parameter correct , In fact, the default is true. If the value is true, Will go to EurekaServer To launch a Rest request , And carry their own metadata information ,Eureka Server It's going to be stored in a double layer Map In structure . first floor Map Of Key Is the service name , The second floor Map Of key Is an instance of a service id.

Renewal of service

After the registration service is completed , The service provider maintains a heartbeat ( Timing to EurekaServer launch Rest request ), tell EurekaServer:“ I'm still alive ”. This is what we call service renewal (renew);

There are two important parameters that can modify the behavior of service renewal :

  • lease-renewal-interval-in-seconds: Renewal of service (renew) The interval of , The default is 30 second

  • lease-expiration-duration-in-seconds: Service expiration time , The default value is 90 second

in other words , By default, each 30 Seconds service will send a heartbeat to the registry , Prove you're alive . If exceeded 90 Seconds without heartbeat ,EurekaServer It would be considered that the service is down , Will be removed from the list of services , Do not modify these two values in the production environment , The default can be .

But in development , This value is a little too long , Often we turn off a service , Will find Eureka Still think service is alive . So we can reduce it properly in the development stage .

example id

Let's take a look at the service status information :

stay Eureka Monitoring the page , View service registration information :

stay status A column , Display the following information :

  • UP(1): The delegate is now activated 1 Example , No cluster

  • DESKTOP-2MVEC12:user-service:8081: Is the name of the example (instance-id),

    • The default format is :${hostname} + ${} + ${server.port}

    • instance-id Is the only standard to distinguish different instances of the same service , So it can't be repeated .

We can go through instance-id Property to modify its composition :

        instance-id: ${}:${server.port}

Restart the service and try again :

4.4. Serving consumers

Get a list of services

When the service consumer starts , Will detect eureka.client.fetch-registry=true The value of the parameter , If true, Will follow Eureka Server List of services read only backup , Then cache locally . also every other 30 second Data will be retrieved and updated . We can modify it with the following parameters :

          registry-fetch-interval-seconds: 5

In production environment , We don't need to change this value .

But for the development environment , Get the latest status of services quickly , We can make it smaller .

.4.5. Failure elimination and self-protection

Failure elimination

Sometimes , Our service provider is not necessarily offline , Possible memory overflow 、 The service fails to work normally due to network failure and other reasons .Eureka Server Such services need to be excluded from the service list . So it turns on a scheduled task , every other 60 Seconds for all retired services ( exceed 90 Seconds not responding ) Culling .

Can pass eureka.server.eviction-interval-timer-in-ms Parameter to modify it , In milliseconds , Do not modify the build environment .

This will bring great inconvenience to our development , You restart the service , Separated 60 second Eureka That's how it came about . The development stage can be adjusted appropriately , such as 10S

Self protection

We shut down a service , Will be in Eureka Panel sees a warning :

It's triggered Eureka Self-protection mechanism . When a service fails to renew its heartbeat on time ,Eureka Will count the latest 15 Does the percentage of service instances with heartbeat failure exceed 85%. In production environment , Because of network delay and other reasons , The proportion of heart failure instances is likely to exceed the standard , But it's not appropriate to exclude services from the list at this time , Because the service may not be down .Eureka The registration information of the current instance will be protected , No rejection . It works in a production environment , Ensures that most services are still available .

But it has brought troubles to our development , So in the development stage, we all turn off the self-protection mode :

           enable-self-preservation: false # Turn off self protection mode ( Open by default )
           eviction-interval-timer-in-ms: 1000 # Interval between scan for failed services ( Default is 60*1000ms)

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