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本文主要研究一下ribbon的ServerListSubsetFilter
ServerListSubsetFilter
ribbon-loadbalancer-2.3.0-sources.jar!/com/netflix/loadbalancer/ServerListSubsetFilter.java
public class ServerListSubsetFilter<T extends Server> extends ZoneAffinityServerListFilter<T> implements IClientConfigAware, Comparator<T>{ private Random random = new Random(); private volatile Set<T> currentSubset = Sets.newHashSet(); private DynamicIntProperty sizeProp = new DynamicIntProperty(DefaultClientConfigImpl.DEFAULT_PROPERTY_NAME_SPACE + ".ServerListSubsetFilter.size", 20); private DynamicFloatProperty eliminationPercent = new DynamicFloatProperty(DefaultClientConfigImpl.DEFAULT_PROPERTY_NAME_SPACE + ".ServerListSubsetFilter.forceEliminatePercent", 0.1f); private DynamicIntProperty eliminationFailureCountThreshold = new DynamicIntProperty(DefaultClientConfigImpl.DEFAULT_PROPERTY_NAME_SPACE + ".ServerListSubsetFilter.eliminationFailureThresold", 0); private DynamicIntProperty eliminationConnectionCountThreshold = new DynamicIntProperty(DefaultClientConfigImpl.DEFAULT_PROPERTY_NAME_SPACE + ".ServerListSubsetFilter.eliminationConnectionThresold", 0); @Override public void initWithNiwsConfig(IClientConfig clientConfig) { super.initWithNiwsConfig(clientConfig); sizeProp = new DynamicIntProperty(clientConfig.getClientName() + "." + clientConfig.getNameSpace() + ".ServerListSubsetFilter.size", 20); eliminationPercent = new DynamicFloatProperty(clientConfig.getClientName() + "." + clientConfig.getNameSpace() + ".ServerListSubsetFilter.forceEliminatePercent", 0.1f); eliminationFailureCountThreshold = new DynamicIntProperty( clientConfig.getClientName() + "." + clientConfig.getNameSpace() + ".ServerListSubsetFilter.eliminationFailureThresold", 0); eliminationConnectionCountThreshold = new DynamicIntProperty(clientConfig.getClientName() + "." + clientConfig.getNameSpace() + ".ServerListSubsetFilter.eliminationConnectionThresold", 0); } /** * Given all the servers, keep only a stable subset of servers to use. This method * keeps the current list of subset in use and keep returning the same list, with exceptions * to relatively unhealthy servers, which are defined as the following: * <p> * <ul> * <li>Servers with their concurrent connection count exceeding the client configuration for * {@code <clientName>.<nameSpace>.ServerListSubsetFilter.eliminationConnectionThresold} (default is 0) * <li>Servers with their failure count exceeding the client configuration for * {@code <clientName>.<nameSpace>.ServerListSubsetFilter.eliminationFailureThresold} (default is 0) * <li>If the servers evicted above is less than the forced eviction percentage as defined by client configuration * {@code <clientName>.<nameSpace>.ServerListSubsetFilter.forceEliminatePercent} (default is 10%, or 0.1), the * remaining servers will be sorted by their health status and servers will worst health status will be * forced evicted. * </ul> * <p> * After the elimination, new servers will be randomly chosen from all servers pool to keep the * number of the subset unchanged. * */ @Override public List<T> getFilteredListOfServers(List<T> servers) { List<T> zoneAffinityFiltered = super.getFilteredListOfServers(servers); Set<T> candidates = Sets.newHashSet(zoneAffinityFiltered); Set<T> newSubSet = Sets.newHashSet(currentSubset); LoadBalancerStats lbStats = getLoadBalancerStats(); for (T server: currentSubset) { // this server is either down or out of service if (!candidates.contains(server)) { newSubSet.remove(server); } else { ServerStats stats = lbStats.getSingleServerStat(server); // remove the servers that do not meet health criteria if (stats.getActiveRequestsCount() > eliminationConnectionCountThreshold.get() || stats.getFailureCount() > eliminationFailureCountThreshold.get()) { newSubSet.remove(server); // also remove from the general pool to avoid selecting them again candidates.remove(server); } } } int targetedListSize = sizeProp.get(); int numEliminated = currentSubset.size() - newSubSet.size(); int minElimination = (int) (targetedListSize * eliminationPercent.get()); int numToForceEliminate = 0; if (targetedListSize < newSubSet.size()) { // size is shrinking numToForceEliminate = newSubSet.size() - targetedListSize; } else if (minElimination > numEliminated) { numToForceEliminate = minElimination - numEliminated; } if (numToForceEliminate > newSubSet.size()) { numToForceEliminate = newSubSet.size(); } if (numToForceEliminate > 0) { List<T> sortedSubSet = Lists.newArrayList(newSubSet); Collections.sort(sortedSubSet, this); List<T> forceEliminated = sortedSubSet.subList(0, numToForceEliminate); newSubSet.removeAll(forceEliminated); candidates.removeAll(forceEliminated); } // after forced elimination or elimination of unhealthy instances, // the size of the set may be less than the targeted size, // then we just randomly add servers from the big pool if (newSubSet.size() < targetedListSize) { int numToChoose = targetedListSize - newSubSet.size(); candidates.removeAll(newSubSet); if (numToChoose > candidates.size()) { // Not enough healthy instances to choose, fallback to use the // total server pool candidates = Sets.newHashSet(zoneAffinityFiltered); candidates.removeAll(newSubSet); } List<T> chosen = randomChoose(Lists.newArrayList(candidates), numToChoose); for (T server: chosen) { newSubSet.add(server); } } currentSubset = newSubSet; return Lists.newArrayList(newSubSet); } /** * Randomly shuffle the beginning portion of server list (according to the number passed into the method) * and return them. * * @param servers * @param toChoose * @return */ private List<T> randomChoose(List<T> servers, int toChoose) { int size = servers.size(); if (toChoose >= size || toChoose < 0) { return servers; } for (int i = 0; i < toChoose; i++) { int index = random.nextInt(size); T tmp = servers.get(index); servers.set(index, servers.get(i)); servers.set(i, tmp); } return servers.subList(0, toChoose); } /** * Function to sort the list by server health condition, with * unhealthy servers before healthy servers. The servers are first sorted by * failures count, and then concurrent connection count. */ @Override public int compare(T server1, T server2) { LoadBalancerStats lbStats = getLoadBalancerStats(); ServerStats stats1 = lbStats.getSingleServerStat(server1); ServerStats stats2 = lbStats.getSingleServerStat(server2); int failuresDiff = (int) (stats2.getFailureCount() - stats1.getFailureCount()); if (failuresDiff != 0) { return failuresDiff; } else { return (stats2.getActiveRequestsCount() - stats1.getActiveRequestsCount()); } }}- ServerListSubsetFilter继承了ZoneAffinityServerListFilter，实现了IClientConfigAware、Comparator接口
- initWithNiwsConfig方法从IClientConfig读取了ServerListSubsetFilter.size、ServerListSubsetFilter.forceEliminatePercent、ServerListSubsetFilter.eliminationFailureThresold、ServerListSubsetFilter.eliminationConnectionThresold配置
- getFilteredListOfServers方法会先调用父类ZoneAffinityServerListFilter的getFilteredListOfServers先过滤出zoneAffinityFiltered作为candidates，然后遍历currentSubset根据ServerStats剔除activeRequestsCount及failureCount超出阈值的server；然后根据numToForceEliminate，以及failureCount排序，使用subList方法得出forceEliminated，然后移除掉，最后randomChoose出来新的newSubSet，然后重置currentSubset
小结
在server list非常多的场景下，没有必要在连接池的保持这么多的连接，ServerListSubsetFilter可以在这种场景下对server list进行精简，通过剔除相对不健康(failureCount、activeRequestCount)的server来达到此目标
doc
- ServerListSubsetFilter