Ribbon负载均衡原理学习记录
ribbon项目通过RestTemplate发起微服务请求,但是知道的都是知道RestTemplate是spring自带的 那么和ribbon有什么关系呢？
标识.png
我们找到了@LoadBalanced标注的负载均衡标识
点进去
loadbalanced.png
@Retention(RetentionPolicy.RUNTIME)
ps:这里标识指的是 当编译完成后 运行保留 在jvm中运行 可以被反射调用
注意上面的绿色注释LoadBalancerClient来配置它
打开LoadBalancerClient类
里面有三个方法
image.png
同时继承了ServiceInstanceChooser 类
字面意思 服务选择实例
public interface LoadBalancerClient extends ServiceInstanceChooser {
/**
* execute request using a ServiceInstance from the LoadBalancer for the specified
* service
* @param serviceId the service id to look up the LoadBalancer
* @param request allows implementations to execute pre and post actions such as
* incrementing metrics
* @return the result of the LoadBalancerRequest callback on the selected
* ServiceInstance
*/
<T> T execute(String serviceId, LoadBalancerRequest<T> request) throws IOException;
/**
* execute request using a ServiceInstance from the LoadBalancer for the specified
* service
* @param serviceId the service id to look up the LoadBalancer
* @param serviceInstance the service to execute the request to
* @param request allows implementations to execute pre and post actions such as
* incrementing metrics
* @return the result of the LoadBalancerRequest callback on the selected
* ServiceInstance
*/
<T> T execute(String serviceId, ServiceInstance serviceInstance, LoadBalancerRequest<T> request) throws IOException;
/**
* Create a proper URI with a real host and port for systems to utilize.
* Some systems use a URI with the logical serivce name as the host,
* such as http://myservice/path/to/service. This will replace the
* service name with the host:port from the ServiceInstance.
* @param instance
* @param original a URI with the host as a logical service name
* @return a reconstructed URI
*/
URI reconstructURI(ServiceInstance instance, URI original);
}
public interface ServiceInstanceChooser {
/**
* Choose a ServiceInstance from the LoadBalancer for the specified service
* @param serviceId the service id to look up the LoadBalancer
* @return a ServiceInstance that matches the serviceId
*/
ServiceInstance choose(String serviceId);
}
ServiceInstance choose(String serviceId); 根据serviceId即服务ID查询服务
<T> T execute(String serviceId, LoadBalancerRequest<T> request) throws IOException; 根据服务来执行请求内容
URI reconstructURI(ServiceInstance instance, URI original);
拼接请求方式 传统中是ip:port 现在是服务名称:port 形式
定位当前类位置 发现相关类
image.png
当然太多了 就不仔细说了 有空自己去看
我们关注自动装配这个类 有关自动装配相关知识 后面再仔细说
/**
* Auto configuration for Ribbon (client side load balancing).
*
* @author Spencer Gibb
* @author Dave Syer
* @author Will Tran
*/
@Configuration
@ConditionalOnClass(RestTemplate.class)
@ConditionalOnBean(LoadBalancerClient.class)
@EnableConfigurationProperties(LoadBalancerRetryProperties.class)
public class LoadBalancerAutoConfiguration {
@LoadBalanced
@Autowired(required = false)
private List<RestTemplate> restTemplates = Collections.emptyList();
@Bean
public SmartInitializingSingleton loadBalancedRestTemplateInitializer(
final List<RestTemplateCustomizer> customizers) {
return new SmartInitializingSingleton() {
@Override
public void afterSingletonsInstantiated() {
for (RestTemplate restTemplate : LoadBalancerAutoConfiguration.this.restTemplates) {
for (RestTemplateCustomizer customizer : customizers) {
customizer.customize(restTemplate);
}
}
}
};
}
@Autowired(required = false)
private List<LoadBalancerRequestTransformer> transformers = Collections.emptyList();
@Bean
@ConditionalOnMissingBean
public LoadBalancerRequestFactory loadBalancerRequestFactory(
LoadBalancerClient loadBalancerClient) {
return new LoadBalancerRequestFactory(loadBalancerClient, transformers);
}
@Configuration
@ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")
static class LoadBalancerInterceptorConfig {
@Bean
public LoadBalancerInterceptor ribbonInterceptor(
LoadBalancerClient loadBalancerClient,
LoadBalancerRequestFactory requestFactory) {
return new LoadBalancerInterceptor(loadBalancerClient, requestFactory);
}
@Bean
@ConditionalOnMissingBean
public RestTemplateCustomizer restTemplateCustomizer(
final LoadBalancerInterceptor loadBalancerInterceptor) {
return new RestTemplateCustomizer() {
@Override
public void customize(RestTemplate restTemplate) {
List<ClientHttpRequestInterceptor> list = new ArrayList<>(
restTemplate.getInterceptors());
list.add(loadBalancerInterceptor);
restTemplate.setInterceptors(list);
}
};
}
}
@Configuration
@ConditionalOnClass(RetryTemplate.class)
public static class RetryAutoConfiguration {
@Bean
public RetryTemplate retryTemplate() {
RetryTemplate template = new RetryTemplate();
template.setThrowLastExceptionOnExhausted(true);
return template;
}
@Bean
@ConditionalOnMissingBean
public LoadBalancedRetryPolicyFactory loadBalancedRetryPolicyFactory() {
return new LoadBalancedRetryPolicyFactory.NeverRetryFactory();
}
@Bean
@ConditionalOnMissingBean
public LoadBalancedBackOffPolicyFactory loadBalancedBackOffPolicyFactory() {
return new LoadBalancedBackOffPolicyFactory.NoBackOffPolicyFactory();
}
}
@Configuration
@ConditionalOnClass(RetryTemplate.class)
public static class RetryInterceptorAutoConfiguration {
@Bean
@ConditionalOnMissingBean
public RetryLoadBalancerInterceptor ribbonInterceptor(
LoadBalancerClient loadBalancerClient, LoadBalancerRetryProperties properties,
LoadBalancedRetryPolicyFactory lbRetryPolicyFactory,
LoadBalancerRequestFactory requestFactory,
LoadBalancedBackOffPolicyFactory backOffPolicyFactory) {
return new RetryLoadBalancerInterceptor(loadBalancerClient, properties,
lbRetryPolicyFactory, requestFactory, backOffPolicyFactory);
}
@Bean
@ConditionalOnMissingBean
public RestTemplateCustomizer restTemplateCustomizer(
final RetryLoadBalancerInterceptor loadBalancerInterceptor) {
return new RestTemplateCustomizer() {
@Override
public void customize(RestTemplate restTemplate) {
List<ClientHttpRequestInterceptor> list = new ArrayList<>(
restTemplate.getInterceptors());
list.add(loadBalancerInterceptor);
restTemplate.setInterceptors(list);
}
};
}
}
}
ps：@ConditionalOnMissingClass当缺少指定的value类时 创建某类
@ConditionalOnClass(RestTemplate.class) RestTemplate类必须存在当前工作环境中
@ConditionalOnBean(LoadBalancerClient.class) 在spring的Bean工程中必须有LoadBalancerClient的实现Bean；
该配置类中 主要做了三件事：
1.创建了一个LoadBalancerInterceptor 负载均衡拦截器 用于对客户端发起的请求进行拦截，以实现客户端负载均衡.
2.创建一个RestTemplateCustomizer的Bean，用于给RestTemplate增加
LoadBalancerInterceptor拦截器。
3.维护被@LoadBananced注解修饰的RestTemplate对象列表，并在初始化，通过调用RestTemplateCustomizer实例来给需要的客户端负载均衡RestTemplate增加拦截器LoadBalancerInterceptor 拦截器
看LoadBalancerInterceptor拦截器是如何将一个普通RestTemplate实现负载均衡的
**
* @author Spencer Gibb
* @author Dave Syer
* @author Ryan Baxter
* @author William Tran
*/
public class LoadBalancerInterceptor implements ClientHttpRequestInterceptor {
private LoadBalancerClient loadBalancer;
private LoadBalancerRequestFactory requestFactory;
public LoadBalancerInterceptor(LoadBalancerClient loadBalancer, LoadBalancerRequestFactory requestFactory) {
this.loadBalancer = loadBalancer;
this.requestFactory = requestFactory;
}
public LoadBalancerInterceptor(LoadBalancerClient loadBalancer) {
// for backwards compatibility
this(loadBalancer, new LoadBalancerRequestFactory(loadBalancer));
}
@Override
public ClientHttpResponse intercept(final HttpRequest request, final byte[] body,
final ClientHttpRequestExecution execution) throws IOException {
final URI originalUri = request.getURI();
String serviceName = originalUri.getHost();
Assert.state(serviceName != null, "Request URI does not contain a valid hostname: " + originalUri);
return this.loadBalancer.execute(serviceName, requestFactory.createRequest(request, body, execution));
}
}
public interface ClientHttpRequestInterceptor {
/**
* Intercept the given request, and return a response. The given {@link ClientHttpRequestExecution} allows
* the interceptor to pass on the request and response to the next entity in the chain.
*
* <p>A typical implementation of this method would follow the following pattern:
* <ol>
* <li>Examine the {@linkplain HttpRequest request} and body</li>
* <li>Optionally {@linkplain org.springframework.http.client.support.HttpRequestWrapper wrap} the request to filter HTTP attributes.</li>
* <li>Optionally modify the body of the request.</li>
* <li><strong>Either</strong>
* <ul>
* <li>execute the request using {@link ClientHttpRequestExecution#execute(org.springframework.http.HttpRequest, byte[])},</li>
* <strong>or</strong>
* <li>do not execute the request to block the execution altogether.</li>
* </ul>
* <li>Optionally wrap the response to filter HTTP attributes.</li>
* </ol>
*
* @param request the request, containing method, URI, and headers
* @param body the body of the request
* @param execution the request execution
* @return the response
* @throws IOException in case of I/O errors
*/
ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution)
throws IOException;
}
可以看到LoadBalancerInterceptor 实现了重写ClientHttpRequestInterceptor Http拦截的请求
可以看到拦截器中注入了LoadBalancerClient的实现.当一个被@LoadBalanced 注解修饰的RestTemplate对象向外发起Http请求时用intercept方法 截取出 由于我们host用的是RPC框架 originalUri.getHost();获取的是服务名 然后在调用之前的LoadBalancerClient execute去执行请求
继续往下 看LoadBalancerClient的execute实现
@Override
public <T> T execute(String serviceId, LoadBalancerRequest<T> request) throws IOException {
ILoadBalancer loadBalancer = getLoadBalancer(serviceId);
Server server = getServer(loadBalancer);
if (server == null) {
throw new IllegalStateException("No instances available for " + serviceId);
}
RibbonServer ribbonServer = new RibbonServer(serviceId, server, isSecure(server,
serviceId), serverIntrospector(serviceId).getMetadata(server));
return execute(serviceId, ribbonServer, request);
}
@Override
public <T> T execute(String serviceId, ServiceInstance serviceInstance, LoadBalancerRequest<T> request) throws IOException {
Server server = null;
if(serviceInstance instanceof RibbonServer) {
server = ((RibbonServer)serviceInstance).getServer();
}
if (server == null) {
throw new IllegalStateException("No instances available for " + serviceId);
}
RibbonLoadBalancerContext context = this.clientFactory
.getLoadBalancerContext(serviceId);
RibbonStatsRecorder statsRecorder = new RibbonStatsRecorder(context, server);
try {
T returnVal = request.apply(serviceInstance);
statsRecorder.recordStats(returnVal);
return returnVal;
}
// catch IOException and rethrow so RestTemplate behaves correctly
catch (IOException ex) {
statsRecorder.recordStats(ex);
throw ex;
}
catch (Exception ex) {
statsRecorder.recordStats(ex);
ReflectionUtils.rethrowRuntimeException(ex);
}
return null;
}
可以看到通过
ILoadBalancer loadBalancer = getLoadBalancer(serviceId);
Server server = getServer(loadBalancer);
获取服务实例
protected Server getServer(ILoadBalancer loadBalancer) {
if (loadBalancer == null) {
return null;
}
return loadBalancer.chooseServer("default"); // TODO: better handling of key
}
image.png
并未使用之前的LoadBalancerClient类的choose来获取
而是使用netflix ribbon来获取
public interface ILoadBalancer {
void addServers(List<Server> var1);
Server chooseServer(Object var1);
void markServerDown(Server var1);
/** @deprecated */
@Deprecated
List<Server> getServerList(boolean var1);
List<Server> getReachableServers();
List<Server> getAllServers();
}
主要是这几个功能
addServers添加服务
chooseServer 选择服务
markServerDown停止服务
getReachableServers 获得正常能访问的服务
getAllServers 获取所有服务 包括dang机的
image.png
ILoadBalancer 的实现扩展以上 而springCloud扩展默认采用ZoneAwareLoadBalancer
image.png
2019年4月8日23:59:53 明天上班 休息了
