In depth exploration of ribbon load balancing

1. Ribbon Load balancing

Study Eruaka When , We added @LoadBalanced annotation , Load balancing function can be realized , What's the principle ？

1.1 Load balancing principle

SpringCloud The bottom layer is actually using a program called Ribbon The components of , To realize the load balancing function .

Then our request is clearly http://userservice/user/1, How did it become http://localhost:8081 What about ？

1.2 Source tracking

Why do we just input service Name can be accessed ？ We need to get ip And port .

Obviously someone helped us according to service name , Get the ip And port . It is LoadBalancerInterceptor, This class will be in the right RestTemplate Request to intercept , And then from Eureka According to the service id Get a list of services , Then we use the load balancing algorithm to get the real service address information , Replace service id.

We are right. LoadBalancerInterceptor Source code tracking ：

1）LoadBalancerInterceptor

You can see... Here intercept Method , Intercepted the user's HttpRequest request , Then I did a few things ：

• request.getURI()： Get request uri, In this case http://user-service/user/8
• originalUri.getHost()： obtain uri Hostname of the path , It's actually service id,user-service
• this.loadBalancer.execute()： Processing services id, And user requests .

there this.loadBalancer yes LoadBalancerClient type , Let's keep up with execute.

1）LoadBalancerClient

find LoadBalancerClient Interface , Continue to follow in execute Method , Find the subclass that implements the interface ：

The code looks like this ：

• getLoadBalancer(serviceId)： According to the service id obtain ILoadBalancer, and ILoadBalancer Will take the service id Go to eureka Get the list of services in and save it .
• getServer(loadBalancer)： Use the built-in load balancing algorithm , Select a... From the list of services . In this case , You can see the capture 8082 Service of port

After release , Visit and track again , We found that 8081：

Sure enough, load balancing is realized .

3） Load balancing strategy IRule

In the code just now , You can see that getting the service through a getServer Method to do load balancing :

Let's keep up with ：

Keep track of source code chooseServer Method , Found such a piece of code ：

Let's look at this rule Who is it? ：

there rule The default is a RoundRobinRule, See the introduction of class ：

That's what polling means .

Come here , We know the whole process of load balancing .

4） summary

SpringCloudRibbon The bottom layer of the uses an interceptor , Intercepted RestTemplate Requests made , Changed the address . Summarize with a picture ：

The basic process is as follows ：

• Intercept our RestTemplate request http://userservice/user/1
• RibbonLoadBalancerClient Will request from url Get the service name from , That is to say user-service
• DynamicServerListLoadBalancer according to user-service To eureka Pull the service list
• eureka Returns a list of ,localhost:8081、localhost:8082
• IRule Leverage built-in load balancing rules , Select one from the list , for example localhost:8081
• RibbonLoadBalancerClient Modify request address , use localhost:8081 replace userservice, obtain http://localhost:8081/user/1, Make a real request

1.3 Load balancing strategy

1.3.1. Load balancing strategy

The rules of load balancing are defined in IRule Interface , and IRule There are many different implementation classes ：

The meaning of different rules is as follows ：

Built in load balancing rule class	Rule description
RoundRobinRule	Simply poll the list of services to select the server . It is Ribbon Default load balancing rules .
AvailabilityFilteringRule	Ignore the following two servers ： （1） By default , This server if 3 Secondary connection failed , This server will be set to “ A short circuit ” state . The short circuit condition will continue 30 second , If the connection fails again , The duration of the short circuit will increase geometrically . （2） Servers with too many concurrent . If a server has too many concurrent connections , Configured with AvailabilityFilteringRule The client side of the rule will also ignore it . Maximum number of concurrent connections , It can be done by ..ActiveConnectionsLimit Property configuration .
WeightedResponseTimeRule	Give each server a weight value . The longer the server response time , The less weight this server has . This rule randomly selects servers , This weight value will affect the choice of the server .
ZoneAvoidanceRule	Select servers based on servers available in the region . Use Zone Classify servers , This Zone It can be understood as a computer room 、 A rack, etc . And then on Zone Polling multiple services in the .
BestAvailableRule	Ignore those short circuited servers , And choose a server with a lower number of concurrent .
RandomRule	Randomly select an available server .
RetryRule	The choice logic of retry mechanism

The default implementation is ZoneAvoidanceRule, Is a polling scheme

1.3.2. Custom load balancing policies

By defining IRule The implementation can modify the load balancing rules , There are two ways ：

1. Code mode ： stay order-service Medium OrderApplication Class , Define a new IRule：

   @Bean
   public IRule randomRule(){
         
       return new RandomRule();
   }
   

2. Configuration file mode ： stay order-service Of application.yml In file , Adding a new configuration can also modify the rules ：

   userservice: #  Configure load balancing rules for a microservice , Here is userservice service 
     ribbon:
       NFLoadBalancerRuleClassName: com.netflix.loadbalancer.RandomRule #  Load balancing rules  
   

Be careful , Generally, the default load balancing rules are used , No modification .

1.4 Hunger is loaded

Ribbon The default is lazy loading , That is, the first time you visit, you will create LoadBalanceClient, The request will take a long time .

First request :1s

It's very fast to ask again ：

Hunger loading will be created when the project starts , Reduce the time-consuming of the first visit , Enable hungry loading through the following configuration ：

ribbon:
  eager-load:
    enabled: true
    clients: userservice