引言
Spring Cloud Ribbon 解決負載均衡的迷惑
代碼準備
依賴關係
+------------+ +------------+
| | | |
| | | |
| | | |
| | | |
| consumer +------------> | provider |
| | RestTemplate | |
| | | |
| | | |
| | | |
+------------+ +------------+
複製代碼
pom 依賴
加入nacos 服務發現即可，內部引用了spring-cloud-ribbon相關依賴
<dependency>
<groupId>com.alibaba.cloud</groupId>
<artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
</dependency>
複製代碼
調用客戶端
我們這裏以最簡單的 RestTemplate 調用開始使用Ribbon
@Bean
@LoadBalanced
public RestTemplate restTemplate() {
return new RestTemplate();
}
// Controller 使用restTemplate 調用服務提供方接口
ResponseEntity<String> forEntity = restTemplate.getForEntity("http://provider/req", String.class);
複製代碼
源碼解析
創建調用攔截器
1. 獲取全部 @LoadBalanced標記的RestTemplate
public class LoadBalancerAutoConfiguration {
@LoadBalanced
@Autowired(required = false)
private List<RestTemplate> restTemplates = Collections.emptyList();
}
複製代碼
2. 增加 LoadBalancerInterceptor 處理邏輯
- 沒有引入 spring-retry使用的是
@Bean
public LoadBalancerInterceptor ribbonInterceptor() {
return new LoadBalancerInterceptor();
}
複製代碼
- 引入 spring-retry 使用的是
@Bean
@ConditionalOnMissingBean
public RetryLoadBalancerInterceptor ribbonInterceptor() {
return new RetryLoadBalancerInterceptor();
}
複製代碼
- LoadBalancerInterceptor 業務邏輯
public class LoadBalancerInterceptor implements ClientHttpRequestInterceptor {
@Override
public ClientHttpResponse intercept() {
final URI originalUri = request.getURI();
// http://demo-provider/req 截取 demo-provider 服務名稱
String serviceName = originalUri.getHost();
// 默認注入的 RibbonAutoConfiguration.RibbonLoadBalancerClient
return this.loadBalancer.execute(serviceName,
// 創建請求對象
this.requestFactory.createRequest(request, body, execution));
}
}
複製代碼
執行攔截器
3. RibbonLoadBalancerClient執行
//RibbonAutoConfiguration默認注入的RibbonLoadBalancerClient
@Bean
@ConditionalOnMissingBean(LoadBalancerClient.class)
public LoadBalancerClient loadBalancerClient() {
return new RibbonLoadBalancerClient(springClientFactory());
}
複製代碼
4.execute執行
public class RibbonLoadBalancerClient implements LoadBalancerClient {
public <T> T execute(){
//獲取具體的ILoadBalancer實現
ILoadBalancer loadBalancer = getLoadBalancer(serviceId);
// 調用ILoadBalancer 實現獲取Server
Server server = getServer(loadBalancer, hint);
RibbonServer ribbonServer = new RibbonServer(serviceId, server,
isSecure(server, serviceId),
serverIntrospector(serviceId).getMetadata(server));
//獲取狀態記錄器，保存此次選取的server
RibbonLoadBalancerContext context = this.clientFactory
.getLoadBalancerContext(serviceId);
RibbonStatsRecorder statsRecorder = new RibbonStatsRecorder(context, server);
T returnVal = request.apply(serviceInstance);
statsRecorder.recordStats(returnVal);
return returnVal;
}
}
複製代碼
獲取ILoadBalancer
5 SpringClientFactory
// bean 工廠生成LoadBalancer 的實現
protected ILoadBalancer getLoadBalancer(String serviceId) {
return this.springClientFactory.getLoadBalancer(serviceId);
}
// 具體生成邏輯看 RibbonClientConfiguration，這個Bean 只有工廠調用的時候纔會創建
@Bean
@ConditionalOnMissingBean
public ILoadBalancer ribbonLoadBalancer(IClientConfig config,
ServerList<Server> serverList, ServerListFilter<Server> serverListFilter,
IRule rule, IPing ping, ServerListUpdater serverListUpdater) {
return new ZoneAwareLoadBalancer<>();
}
複製代碼
6.創建LoadBalancer 的依賴要素
名稱 默認實現 作用 IClientConfig DefaultClientConfigImpl ribbon 客戶端配置參數，例如： 超時設置、壓縮設置等 ServerList NacosServerList 目標服務的實例實例表，具體服務發現客戶端實現 ServerListFilter ZonePreferenceServerListFilter 針對ServerList 實例列表的過濾邏輯處理 IRule ZoneAvoidanceRule 負載均衡選擇Server 的規則 IPing DummyPing 檢驗服務是否可用的方法實現 ServerListUpdater PollingServerListUpdater 針對ServerList 更新的操作實現
以上默認實現參考 RibbonClientConfiguration. ZoneAwareLoadBalancer
獲取服務實例
//Server server = getServer(loadBalancer, hint); 4. excute 方法
protected Server getServer(ILoadBalancer loadBalancer, Object hint) {
return loadBalancer.chooseServer(hint != null ? hint : "default");
}
複製代碼
7. ZoneAwareLoadBalancer
public class ZoneAwareLoadBalancer{
public ZoneAwareLoadBalancer() {
// 調用父類初始化方法。 這裏會開啓實例維護的定時任務等 （具體解析參考 擴展部分）
super(clientConfig, rule, ping, serverList, filter, serverListUpdater);
}
@Override
public Server chooseServer(Object key) {
// 若是使用的 Nacos 服務發現，則沒有 Zone 的概念，直接調用父類的實現
if (!ENABLED.get() || getLoadBalancerStats().getAvailableZones().size() <= 1) {
return super.chooseServer(key);
}
// 以下爲有 Zone 的概念 例如 Eureka （具體）
...
return server;
}
}
複製代碼
- 父類調用IRule實現選擇Server
public Server chooseServer(Object key) {
return rule.choose(key);
}
複製代碼
8.PredicateBasedRule 選擇規則
public abstract class PredicateBasedRule {
@Override
public Server choose(Object key) {
ILoadBalancer lb = getLoadBalancer();
// 獲取斷言配置
Optional<Server> server = getPredicate().chooseRoundRobinAfterFiltering(lb.getAllServers(), key);
if (server.isPresent()) {
return server.get();
} else {
return null;
}
}
}
複製代碼
9. ZoneAvoidancePredicate服務列表斷言
public class ZoneAvoidancePredicate {
@Override
public boolean apply(@Nullable PredicateKey input) {
if (!ENABLED.get()) {
return true;
}
// 還是獲取區域配置，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;
}
// 區域高可用判斷
...
}
}
複製代碼
擴展: ServerList 維護
初始化ServerList
在上文 6.創建LoadBalancer 的依賴要素，中 ServerList 目標服務的實例實例表，具體服務發現客戶端實現。我們來看下 Nacos 的實現
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();
//調用nacos-sdk 查詢實例列表
List<Instance> instances = discoveryProperties.namingServiceInstance()
.selectInstances(serviceId, group, true);
// 類型轉換
return instancesToServerList(instances);
}
}
複製代碼
更新ServerListUpdater
- ServerList 初始化後更新操作通過 PollingServerListUpdater
public class PollingServerListUpdater implements ServerListUpdater {
@Override
public synchronized void start(final UpdateAction updateAction) {
// 更新任務 交給updateAction 具體實現
final Runnable wrapperRunnable = () -> {
updateAction.doUpdate();
lastUpdated = System.currentTimeMillis();
};
// 開啓後臺線程定時執行 updateAction
scheduledFuture = getRefreshExecutor().scheduleWithFixedDelay(
wrapperRunnable,
initialDelayMs,
refreshIntervalMs,
TimeUnit.MILLISECONDS
);
}
}
複製代碼
- updateAction 實現
public void doUpdate() {
DynamicServerListLoadBalancer.this.updateListOfServers();
}
複製代碼
public class PollingServerListUpdater implements ServerListUpdater {
public void updateListOfServers() {
List<T> servers = new ArrayList();
// 調用NacosServiceList 獲取全部服務列表
servers = this.serverListImpl.getUpdatedListOfServers();
// 如果配置實例過濾器在執行過濾
if (this.filter != null) {
servers = this.filter.getFilteredListOfServers((List)servers);
}
// 更新LoadBalancer 服務列表
this.updateAllServerList((List)servers);
}
}
複製代碼
擴展: Server 狀態維護
- LoadBalancer 初始構造時會觸發 setupPingTask()
public BaseLoadBalancer() {
this.name = DEFAULT_NAME;
this.ping = null;
setRule(DEFAULT_RULE);
// 開啓ping 檢查任務
setupPingTask();
lbStats = new LoadBalancerStats(DEFAULT_NAME);
}
複製代碼
- setupPingTask
void setupPingTask() {
// 是否可以ping, 默認的DummyPing 直接 跳過不執行
if (canSkipPing()) {
return;
}
// 執行PingTask
lbTimer.schedule(new BaseLoadBalancer.PingTask(), 0, pingIntervalSeconds * 1000);
// 開啓任務
new BaseLoadBalancer.Pinger(pingStrategy).runPinger();
}
複製代碼
- SerialPingStrategy 串行執行邏輯
// 串行調度執行 Iping 邏輯
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;
}
}
複製代碼
- 調用url 判斷可用性
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;
}
}
複製代碼
擴展: RibbonClient 懶加載處理
由上文可知，默認情況下 Ribbon 在第一次請求才會去創建 LoadBalancer ，這種懶加載機制會導致服務啓動後，第一次調用服務延遲問題，甚至在整合 斷路器（hystrix）等出現超時熔斷 。
爲了解決這個問題，我們會配置 Ribbon 的飢餓加載
ribbon:
eager-load:
clients:
- provider
複製代碼
- RibbonApplicationContextInitializer 服務啓動後自動調用 工廠提前創建需要的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();
}
}