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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
