代码准备
依赖关系
pom 依赖
加入nacos 服务发现即可，内部引用了spring-cloud-ribbon相关依赖
<dependency>
<groupId>com.alibaba.cloud</groupId>
<artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
</dependency>
调用客户端
我们这里以最简单的 RestTemplate 调用开始使用Ribbon
@Bean
@LoadBalanced
public RestTemplate restTemplate() {
return new RestTemplate();
}
// Controller 使用restTemplate 调用服务提供方接口
ResponseEntity<String> forEntity = restTemplate.getForEntity("http://provider/req", String.class);
源码解析
创建调用拦截器
1. 获取全部 @LoadBalanced标记的RestTemplate
public class LoadBalancerAutoConfiguration {
@LoadBalanced
@Autowired(required = false)
private List<RestTemplate> restTemplates = Collections.emptyList();
}
2. 增加 LoadBalancerInterceptor 处理逻辑
没有引入 spring-retry使用的是
@BeanpublicLoadBalancerInterceptorribbonInterceptor(){
return new LoadBalancerInterceptor();
}
引入 spring-retry 使用的是
@Bean
@ConditionalOnMissingBean
public RetryLoadBalancerInterceptor ribbonInterceptor() {
return new RetryLoadBalancerInterceptor();
}
LoadBalancerInterceptor 业务逻辑
public class LoadBalancerInterceptor implements ClientHttpRequestInterceptor {
@Override
public ClientHttpResponse intercept() {
final URI originalUri = request.getURI();
// http://demo-provider/req 截取 demo-provider 服务名称
String serviceName = originalUri.getHost();
// 默认注入的 RibbonAutoConfiguration.RibbonLoadBalancerClient
return this.loadBalancer.execute(serviceName,
// 创建请求对象
this.requestFactory.createRequest(request, body, execution));
}
}
执行拦截器
3. RibbonLoadBalancerClient执行
//RibbonAutoConfiguration默认注入的RibbonLoadBalancerClient
@Bean
@ConditionalOnMissingBean(LoadBalancerClient.class)
public LoadBalancerClient loadBalancerClient() {
return new RibbonLoadBalancerClient(springClientFactory());
}
4.execute执行
public class RibbonLoadBalancerClient implements LoadBalancerClient {
public <T> T execute(){
//获取具体的ILoadBalancer实现
ILoadBalancer loadBalancer = getLoadBalancer(serviceId);
// 调用ILoadBalancer 实现获取Server
Server server = getServer(loadBalancer, hint);
RibbonServer ribbonServer = new RibbonServer(serviceId, server,
isSecure(server, serviceId),
serverIntrospector(serviceId).getMetadata(server));
//获取状态记录器，保存此次选取的server
RibbonLoadBalancerContext context = this.clientFactory
.getLoadBalancerContext(serviceId);
RibbonStatsRecorder statsRecorder = new RibbonStatsRecorder(context, server);
T returnVal = request.apply(serviceInstance);
statsRecorder.recordStats(returnVal);
return returnVal;
}
}
获取ILoadBalancer
5 SpringClientFactory
// bean 工厂生成LoadBalancer 的实现
protected ILoadBalancer getLoadBalancer(String serviceId) {
return this.springClientFactory.getLoadBalancer(serviceId);
}
// 具体生成逻辑看 RibbonClientConfiguration，这个Bean 只有工厂调用的时候才会创建
@Bean
@ConditionalOnMissingBean
public ILoadBalancer ribbonLoadBalancer(IClientConfig config,
ServerList<Server> serverList, ServerListFilter<Server> serverListFilter,
IRule rule, IPing ping, ServerListUpdater serverListUpdater) {
return new ZoneAwareLoadBalancer<>();
}
6.创建LoadBalancer 的依赖要素
以上默认实现参考 RibbonClientConfiguration. ZoneAwareLoadBalancer
获取服务实例
//Server server = getServer(loadBalancer, hint); 4. excute 方法
protected Server getServer(ILoadBalancer loadBalancer, Object hint) {
return loadBalancer.chooseServer(hint != null ? hint : "default");
}
7. ZoneAwareLoadBalancer
public class ZoneAwareLoadBalancer{
public ZoneAwareLoadBalancer() {
// 调用父类初始化方法。 这里会开启实例维护的定时任务等 （具体解析参考 扩展部分）
super(clientConfig, rule, ping, serverList, filter, serverListUpdater);
}
@Override
public Server chooseServer(Object key) {
// 若是使用的 Nacos 服务发现，则没有 Zone 的概念，直接调用父类的实现
if (!ENABLED.get() || getLoadBalancerStats().getAvailableZones().size() <= 1) {
return super.chooseServer(key);
}
// 以下为有 Zone 的概念 例如 Eureka （具体）
...
return server;
}
}
父类调用IRule实现选择Server
public Server chooseServer(Object key) {
return rule.choose(key);
}
8.PredicateBasedRule 选择规则
public abstract class PredicateBasedRule {
@Override
public Server choose(Object key) {
ILoadBalancer lb = getLoadBalancer();
// 获取断言配置
Optional<Server> server = getPredicate().chooseRoundRobinAfterFiltering(lb.getAllServers(), key);
if (server.isPresent()) {
return server.get();
} else {
return null;
}
}
}
9. ZoneAvoidancePredicate服务列表断言
public class ZoneAvoidancePredicate {
@Override
public boolean apply(@Nullable PredicateKey input) {
if (!ENABLED.get()) {
return true;
}
// 还是获取区域配置，如是使用的 Nacos 直接返回true
String serverZone = input.getServer().getZone();
if (serverZone == null) {
// there is no zone information from the server, we do not want to filter
// out this server
return true;
}
// 区域高可用判断
...
}
}
扩展: ServerList 维护
初始化ServerList
在上文 6.创建LoadBalancer 的依赖要素，中 ServerList 目标服务的实例实例表，具体服务发现客户端实现。我们来看下 Nacos 的实现
public class NacosServerList extends AbstractServerList<NacosServer> {
@Override
public List<NacosServer> getInitialListOfServers() {
return getServers();
}
@Override
public List<NacosServer> getUpdatedListOfServers() {
return getServers();
}
private List<NacosServer> getServers() {
String group = discoveryProperties.getGroup();
//调用nacos-sdk 查询实例列表
List<Instance> instances = discoveryProperties.namingServiceInstance()
.selectInstances(serviceId, group, true);
// 类型转换
return instancesToServerList(instances);
}
}
更新ServerListUpdater
ServerList 初始化后更新操作通过 PollingServerListUpdater
public class PollingServerListUpdater implements ServerListUpdater {
@Override
public synchronized void start(final UpdateAction updateAction) {
// 更新任务 交给updateAction 具体实现
final Runnable wrapperRunnable = () -> {
updateAction.doUpdate();
lastUpdated = System.currentTimeMillis();
};
// 开启后台线程定时执行 updateAction
scheduledFuture = getRefreshExecutor().scheduleWithFixedDelay(
wrapperRunnable,
initialDelayMs,
refreshIntervalMs,
TimeUnit.MILLISECONDS
);
}
}
updateAction 实现
public void doUpdate() {
DynamicServerListLoadBalancer.this.updateListOfServers();
}
public class PollingServerListUpdater implements ServerListUpdater {
public void updateListOfServers() {
List<T> servers = new ArrayList();
// 调用NacosServiceList 获取全部服务列表
servers = this.serverListImpl.getUpdatedListOfServers();
// 如果配置实例过滤器在执行过滤
if (this.filter != null) {
servers = this.filter.getFilteredListOfServers((List)servers);
}
// 更新LoadBalancer 服务列表
this.updateAllServerList((List)servers);
}
}
扩展: Server 状态维护
LoadBalancer 初始构造时会触发 setupPingTask()
public BaseLoadBalancer() {
this.name = DEFAULT_NAME;
this.ping = null;
setRule(DEFAULT_RULE);
// 开启ping 检查任务
setupPingTask();
lbStats = new LoadBalancerStats(DEFAULT_NAME);
}
setupPingTask
void setupPingTask() {
// 是否可以ping, 默认的DummyPing 直接 跳过不执行
if (canSkipPing()) {
return;
}
// 执行PingTask
lbTimer.schedule(new BaseLoadBalancer.PingTask(), 0, pingIntervalSeconds * 1000);
// 开启任务
new BaseLoadBalancer.Pinger(pingStrategy).runPinger();
}
SerialPingStrategy 串行执行逻辑
// 串行调度执行 Iping 逻辑
private static class SerialPingStrategy implements IPingStrategy {
@Override
public boolean[] pingServers(IPing ping, Server[] servers) {
int numCandidates = servers.length;
boolean[] results = new boolean[numCandidates];
for (int i = 0; i < numCandidates; i++) {
results[i] = false; /* Default answer is DEAD. */
if (ping != null) {
results[i] = ping.isAlive(servers[i]);
}
}
return results;
}
}
调用url 判断可用性
public class PingUrl implements IPing {
public boolean isAlive(Server server) {
urlStr = urlStr + server.getId();
urlStr = urlStr + this.getPingAppendString();
boolean isAlive = false;
HttpClient httpClient = new DefaultHttpClient();
HttpUriRequest getRequest = new HttpGet(urlStr);
String content = null;
HttpResponse response = httpClient.execute(getRequest);
content = EntityUtils.toString(response.getEntity());
isAlive = response.getStatusLine().getStatusCode() == 200;
return isAlive;
}
}
扩展: RibbonClient 懒加载处理
由上文可知，默认情况下 Ribbon 在第一次请求才会去创建LoadBalancer，这种懒加载机制会导致服务启动后，第一次调用服务延迟问题，甚至在整合 断路器（hystrix）等出现超时熔断 。
为了解决这个问题，我们会配置 Ribbon 的饥饿加载
ribbon:
eager-load:
clients:
- provider
RibbonApplicationContextInitializer 服务启动后自动调用 工厂提前创建需要的ribbon clients
public class RibbonApplicationContextInitializer
implements ApplicationListener<ApplicationReadyEvent> {
private final List<String> clientNames;
protected void initialize() {
if (clientNames != null) {
for (String clientName : clientNames) {
this.springClientFactory.getContext(clientName);
}
}
}
@Override
public void onApplicationEvent(ApplicationReadyEvent event) {
initialize();
}
}
以上内容都是我自己的一些感想，分享出来欢迎大家指正，顺便求一波关注，有想法的伙伴可以评论或者私信我哦~
作者：冷冷gg
链接：https://juejin.im/post/5e5c598551882549052f49e4
来源：掘金
