Shulou(Shulou.com)06/03 Report--

IRule is a strategy for selecting services.

IRule

Public interface IRule {/ * choose one alive server from lb.allServers or * lb.upServers according to key * * @ return choosen Server object. NULL is returned if none * server is available * / public Server choose (Object key); public void setLoadBalancer (ILoadBalancer lb); public ILoadBalancer getLoadBalancer ();}

Choose selects the available services.

RandomRule

Randomly select a UP service.

Random rand; / / Random counter public RandomRule () {rand = new Random ();} public Server choose (ILoadBalancer lb, Object key) {. List upList = lb.getReachableServers (); List allList = lb.getAllServers (); int index = rand.nextInt (serverCount); / / randomly select a server = upList.get (index);...}

RoundRobinRule

Poll for services.

Public RoundRobinRule () {nextServerCyclicCounter = new AtomicInteger (0); / / int thread safety counter} public Server choose (ILoadBalancer lb, Object key) {... Int nextServerIndex = incrementAndGetModulo (serverCount); / / nextServerCyclicCounter gets services backward in turn. Server = allServers.get (nextServerIndex);...} / / polling method private int incrementAndGetModulo (int modulo) {for (;;) {int current = nextServerCyclicCounter.get (); int next = (current + 1)% modulo; if (nextServerCyclicCounter.compareAndSet (current, next)) return next;}

BestAvailableRule

Skip the service of the circuit breaker and get the service with the least number of requests. It is usually used with ServerListSubsetFilter.

Public Server choose (Object key) {if (loadBalancerStats = = null) {return super.choose (key); / / if there is no loadBalancerStats, RoundRibonRule. } List serverList = getLoadBalancer (). GetAllServers (); int minimalConcurrentConnections = Integer.MAX_VALUE; long currentTime = System.currentTimeMillis (); Server chosen = null; for (Server server: serverList) {ServerStats serverStats = loadBalancerStats.getSingleServerStat (server); if (! serverStats.isCircuitBreakerTripped (currentTime)) {int concurrentConnections = serverStats.getActiveRequestsCount (currentTime); if (concurrentConnections

< minimalConcurrentConnections) { minimalConcurrentConnections = concurrentConnections; chosen = server; } } } if (chosen == null) { return super.choose(key); } else { return chosen; }} WeightedResponseTimeRule 权重的方式挑选服务.服务实例响应时间越小的服务,则更容易被选中.如果服务实例响应的时间相差不大的,排在前面的服务实例更容易被选中. // 继承了RoundRobinRule,也就是当WeightedResponseTimeRule不满足条件的时候,则采用RoundRobinRule的方式.public class WeightedResponseTimeRule extends RoundRobinRule {// 这个方式很重要,就是定时的计算每个服务实例的响应时间,并以此作为每个服务实例的权重.void initialize(ILoadBalancer lb) { if (serverWeightTimer != null) { serverWeightTimer.cancel(); } serverWeightTimer = new Timer("NFLoadBalancer-serverWeightTimer-" + name, true); serverWeightTimer.schedule(new DynamicServerWeightTask(), 0,serverWeightTaskTimerInterval); // do a initial run ServerWeight sw = new ServerWeight(); sw.maintainWeights(); Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() { public void run() { logger.info("Stopping NFLoadBalancer-serverWeightTimer-"+ name); serverWeightTimer.cancel(); } }));}// 定时任务内部类class DynamicServerWeightTask extends TimerTask { public void run() { ServerWeight serverWeight = new ServerWeight(); try { serverWeight.maintainWeights(); } catch (Exception e) { logger.error("Error running DynamicServerWeightTask for {}", name, e); } }}// 计算服务实例权重的核心方法.class ServerWeight { public void maintainWeights() { ILoadBalancer lb = getLoadBalancer(); if (lb == null) { return; } if (!serverWeightAssignmentInProgress.compareAndSet(false, true)) { return; } try { logger.info("Weight adjusting job started"); AbstractLoadBalancer nlb = (AbstractLoadBalancer) lb; LoadBalancerStats stats = nlb.getLoadBalancerStats(); if (stats == null) { // no statistics, nothing to do return; } double totalResponseTime = 0; // find maximal 95% response time for (Server server : nlb.getAllServers()) { // this will automatically load the stats if not in cache ServerStats ss = stats.getSingleServerStat(server); totalResponseTime += ss.getResponseTimeAvg(); } // weight for each server is (sum of responseTime of all servers - responseTime) // so that the longer the response time, the less the weight and the less likely to be chosen Double weightSoFar = 0.0; // create new list and hot swap the reference List finalWeights = new ArrayList(); for (Server server : nlb.getAllServers()) { ServerStats ss = stats.getSingleServerStat(server); double weight = totalResponseTime - ss.getResponseTimeAvg(); // 平均响应时间越短,则权重越大,就越容易被选中. weightSoFar += weight; finalWeights.add(weightSoFar); } setWeights(finalWeights); } catch (Exception e) { logger.error("Error calculating server weights", e); } finally { serverWeightAssignmentInProgress.set(false); } }}public Server choose(ILoadBalancer lb, Object key) { ... // 根据权重选择服务的核心代码 double randomWeight = random.nextDouble() * maxTotalWeight; // pick the server index based on the randomIndex int n = 0; for (Double d : currentWeights) { if (d >

= randomWeight) {serverIndex = n; break;} else {server = allList.get (serverIndex);.}}

RetryRule

On the basis of RoundRobinRule, the mechanism of retry is added.

ZoneAvoidanceRule

Use ZoneAvoidancePredicate and AvailabilityPredicate to determine whether to select a server, the former to determine whether the performance of a zone is available, eliminate unavailable zone (all server), and AvailabilityPredicate is used to filter out Server with too many connections.

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