1 调用流程图
在spring cloud alibaba中，nacos discover提供了对ribbon的支持，其方式和eureka client对ribbon的支持一样，而ResTemplate客户端负载均衡又是依赖ribbon，下图是看完源码后画的一张简要的流程图：
2 流程图的源码分析
2.1 调用从RestTemplate到LoadBalancerInterceptor
从RestTemplate:getForObject()一路断点到 doExecute()方法
protected <T> T doExecute(URI url, @Nullable HttpMethod method, @Nullable RequestCallback requestCallback,
@Nullable ResponseExtractor<T> responseExtractor) throws RestClientException {
Assert.notNull(url, "URI is required");
Assert.notNull(method, "HttpMethod is required");
ClientHttpResponse response = null;
try {
ClientHttpRequest request = createRequest(url, method);
if (requestCallback != null) {
requestCallback.doWithRequest(request);
}
response = request.execute();
handleResponse(url, method, response);
return (responseExtractor != null ? responseExtractor.extractData(response) : null);
}
catch (IOException ex) {
…………
}
finally {
if (response != null) {
response.close();
}
}
}
在request处端点可以发现request对象里的List<ClientHttpRequestInterceptor> interceptors中已经包含了LoadBalancerInterceptor这拦截器。
接着从request.execute()一路断点到executeInternal()
@Override
protected final ClientHttpResponse executeInternal(HttpHeaders headers, byte[] bufferedOutput) throws IOException {
InterceptingRequestExecution requestExecution = new InterceptingRequestExecution();
return requestExecution.execute(this, bufferedOutput);
}
private class InterceptingRequestExecution implements ClientHttpRequestExecution {
private final Iterator<ClientHttpRequestInterceptor> iterator;
public InterceptingRequestExecution() {
this.iterator = interceptors.iterator();
}
@Override
public ClientHttpResponse execute(HttpRequest request, byte[] body) throws IOException {
if (this.iterator.hasNext()) {
ClientHttpRequestInterceptor nextInterceptor = this.iterator.next();
//LoadBalancerInterceptor开始介入
return nextInterceptor.intercept(request, body, this);
}
可以看到在其子类InterceptingRequestExecution的execute方法中LoadBalancerInterceptor的intercept方法。
@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);
//this.loadBalancer为RibbonLoadBalancerClient
//his.requestFactory为LoadBalancerRequestFactory
return this.loadBalancer.execute(serviceName,
this.requestFactory.createRequest(request, body, execution));
}
到此为止代码已经走到流程图中的第步，Ribbon开始介入。
-------------到此为止进行到开篇流程图中的第④步--------------------------
2.2 RibbonLoadBalancerClient执行源码
从2.1 末尾代码中的this.loadBalancer.execute()一路狂奔到下面的execute方法，ribbon的核心逻辑的入口就在这：
public <T> T execute(String serviceId, LoadBalancerRequest<T> request, Object hint)
throws IOException {
ILoadBalancer loadBalancer = getLoadBalancer(serviceId);
Server server = getServer(loadBalancer, hint);
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);
}
2.2.1 ILoadBalancer默认实现ZoneAwareLoadBalancer的创建
断点进入getLoadBalancer(serviceId);
这里的serviceId为需要调用的服务，即服务提供段在nacos server 中注册的spring.application.name
protected ILoadBalancer getLoadBalancer(String serviceId) {
return this.clientFactory.getLoadBalancer(serviceId);
}
这个默认创建的ILoadBalancer，默认为：ZoneAwareLoadBalancer，创建过程复杂，先看一张截图：
可以看到在this.clientFactory中有一个contexts的ConcurrentHashp，key为serviceId,value则为对应的applicationContext，在首次访问 serviceId 时创建对应的applicationCotext，并将该serviceId下ribbon路由的对象放在自己的applicationContext以达到隔离的目的。
下面贴出部分关键代码：
断点到spring factory的createContext方法，
protected AnnotationConfigApplicationContext createContext(String name) {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
if (this.configurations.containsKey(name)) {
for (Class<?> configuration : this.configurations.get(name)
.getConfiguration()) {
context.register(configuration);
}
}
for (Map.Entry<String, C> entry : this.configurations.entrySet()) {
if (entry.getKey().startsWith("default.")) {
for (Class<?> configuration : entry.getValue().getConfiguration()) {
context.register(configuration);
}
}
}
context.register(PropertyPlaceholderAutoConfiguration.class,
this.defaultConfigType);
context.getEnvironment().getPropertySources().addFirst(new MapPropertySource(
this.propertySourceName,
Collections.<String, Object>singletonMap(this.propertyName, name)));
if (this.parent != null) {
// Uses Environment from parent as well as beans
context.setParent(this.parent);
// jdk11 issue
// https://github.com/spring-cloud/spring-cloud-netflix/issues/3101
context.setClassLoader(this.parent.getClassLoader());
}
context.setDisplayName(generateDisplayName(name));
context.refresh();
return context;
}
代码分析详见
[spring cloud gateway 整合ribbon、nacos discovery 实现负载均衡源码简析]
中的《3源码简析》 这一部分
-------------到此为止进行到开篇流程图中的第⑥步--------------------------
2.2.2 定时刷新ServerList的PollingServerListUpdater
在RibbonClientConfiguration中创建某一个serviceId对应的 ZoneAwareLoadBalancer对象时时会创建一个PollingServerListUpdater类
@Bean
@ConditionalOnMissingBean
public ServerListUpdater ribbonServerListUpdater(IClientConfig config) {
return new PollingServerListUpdater(config);
}
@Bean
@ConditionalOnMissingBean
public ILoadBalancer ribbonLoadBalancer(IClientConfig config,
ServerList<Server> serverList, ServerListFilter<Server> serverListFilter,
IRule rule, IPing ping, ServerListUpdater serverListUpdater) {
if (this.propertiesFactory.isSet(ILoadBalancer.class, name)) {
return this.propertiesFactory.get(ILoadBalancer.class, config, name);
}
return new ZoneAwareLoadBalancer<>(config, rule, ping, serverList,
serverListFilter, serverListUpdater);
}
在ZoneAwareLoadBalancer的创建构造方法中会执行PollingServerListUpdater中的
@Override
public synchronized void start(final UpdateAction updateAction) {
if (isActive.compareAndSet(false, true)) {
final Runnable wrapperRunnable = new Runnable() {
//定时执行的更新ServerList列表的线程
@Override
public void run() {
if (!isActive.get()) {
if (scheduledFuture != null) {
scheduledFuture.cancel(true);
}
return;
}
try {
//关键代码，加断点
updateAction.doUpdate();
lastUpdated = System.currentTimeMillis();
} catch (Exception e) {
logger.warn("Failed one update cycle", e);
}
}
};
//开始定时任务，默认refreshIntervalMs=30000，即每30秒更新一下服务端列表
scheduledFuture = getRefreshExecutor().scheduleWithFixedDelay(
wrapperRunnable,
initialDelayMs,
refreshIntervalMs,
TimeUnit.MILLISECONDS
);
} else {
logger.info("Already active, no-op");
}
}
Nacos Discover对robbon 的支持
从updateAction.doUpdate();断点到
public void updateListOfServers() {
List<T> servers = new ArrayList<T>();
if (serverListImpl != null) {
//这里的serverListImpl为alibaba提供的NacosServerList
servers = serverListImpl.getUpdatedListOfServers();
LOGGER.debug("List of Servers for {} obtained from Discovery client: {}",
getIdentifier(), servers);
if (filter != null) {
servers = filter.getFilteredListOfServers(servers);
LOGGER.debug("Filtered List of Servers for {} obtained from Discovery client: {}",
getIdentifier(), servers);
}
}
updateAllServerList(servers);
}
ServerList serverListImpl为NacosServerList
如图：
spring-cloud-starter-alibaba-nacos-discovery提供了ServerList的创建
@Bean
@ConditionalOnMissingBean
public ServerList<?> ribbonServerList(IClientConfig config, NacosDiscoveryProperties nacosDiscoveryProperties) {
if (this.propertiesFactory.isSet(ServerList.class, config.getClientName())) {
ServerList serverList = (ServerList)this.propertiesFactory.get(ServerList.class, config, config.getClientName());
return serverList;
} else {
NacosServerList serverList = new NacosServerList(nacosDiscoveryProperties);
serverList.initWithNiwsConfig(config);
return serverList;
}
}
现在更新服务列表的任务已经交给nacos discover了。
如果引入spring-cloud-netflix-eureka-client包，则serverListImpl的实现为DomainExtractingServerList
-------------到此为止进行到开篇流程图中的第⑦步--------------------------
2.2 RibbonLoadBalancerClient执行源码 中的ILoadBalancer loadBalancer = getLoadBalancer(serviceId);代码已经完毕。
2.2.3 ZoneAwareLoadBalancer 的 chooseServer详解
从 RibbonLoadBalancerClient类 Server server = getServer(loadBalancer, hint);一路断点狂奔到
关键代码
public Server chooseServer(Object key) {
if (counter == null) {
counter = createCounter();
}
counter.increment();
if (rule == null) {
return null;
} else {
try {
//这里的rule为默认的ZoneAvoidanceRule，可以通过配置文件配置
return rule.choose(key);
} catch (Exception e) {
logger.warn("LoadBalancer [{}]: Error choosing server for key {}", name, key, e);
return null;
}
}
}
核心逻辑如下：
1、从ZoneAwareLoadBalancer中获取对server列表
2、使用配置的路由策略来选择一个服务端给RestTemplate调用
如图：
-------------到此为止进行到开篇流程图中的第⑧步--------------------------
后面代码就没Ribbon、Nacos Discover什么事了，代码执行开篇流程图中的第⑨步返回response.