@Override
public Server chooseServer(Object key) {
if (!ENABLED.get() || getLoadBalancerStats().getAvailableZones().size() <= 1) {
logger.debug("Zone aware logic disabled or there is only one zone");
return super.chooseServer(key);
}
Server server = null;
try {
LoadBalancerStats lbStats = getLoadBalancerStats();
Map<String, ZoneSnapshot> zoneSnapshot = ZoneAvoidanceRule.createSnapshot(lbStats);
logger.debug("Zone snapshots: {}", zoneSnapshot);
if (triggeringLoad == null) {
triggeringLoad =
DynamicPropertyFactory.getInstance()
.getDoubleProperty(
"ZoneAwareNIWSDiscoveryLoadBalancer."
+ this.getName()
+ ".triggeringLoadPerServerThreshold",
0.2d);
}
if (triggeringBlackoutPercentage == null) {
triggeringBlackoutPercentage =
DynamicPropertyFactory.getInstance()
.getDoubleProperty(
"ZoneAwareNIWSDiscoveryLoadBalancer."
+ this.getName()
+ ".avoidZoneWithBlackoutPercetage",
0.99999d);
}
Set<String> availableZones =
ZoneAvoidanceRule.getAvailableZones(
zoneSnapshot, triggeringLoad.get(), triggeringBlackoutPercentage.get());
logger.debug("Available zones: {}", availableZones);
if (availableZones != null && availableZones.size() < zoneSnapshot.keySet().size()) {
String zone = ZoneAvoidanceRule.randomChooseZone(zoneSnapshot, availableZones);
logger.debug("Zone chosen: {}", zone);
if (zone != null) {
BaseLoadBalancer zoneLoadBalancer = getLoadBalancer(zone);
server = zoneLoadBalancer.chooseServer(key);
}
}
} catch (Throwable e) {
logger.error("Unexpected exception when choosing server using zone aware logic", e);
}
if (server != null) {
return server;
} else {
logger.debug("Zone avoidance logic is not invoked.");
return super.chooseServer(key);
}
}
/**
* @param availableServerStats the server instances to choose from
* @return the nearest, less loaded server instance
* @see {@link LoadBalancer#choose(java.util.List)}
*/
@Override
public ServerStats choose(List<ServerStats> availableServerStats) {
// cache properties to speed up loop
double maxRequestsPerSecond = propMaxRequestsPerSecond.get();
double escapeAreaThreshold = propEscapeAreaThreshold.get();
double escapeRegionThreshold = propEscapeRegionThreshold.get();
double escapeAvailabilityThreshold = propEscapeAvailabilityThreshold.get();
// find the best available server
MetaData max = null;
for (ServerStats stat : availableServerStats) {
ServerStats s = (ServerStats) stat;
ServerInstance instance = s.getServerInstance();
MetaData meta = new MetaData();
meta.location = locations.getUnchecked(s);
meta.server = s;
meta.load = s.getSentMessagesPerSecond() / maxRequestsPerSecond;
meta.sessionCount = s.getOpenSessionsCount();
meta.locationBits = 0;
if (myLocation.getAvailabilityZone().equals(meta.location.getAvailabilityZone())) {
// same availability zone
meta.locationBits = 7;
} else if (myLocation.getRegion().equals(meta.location.getRegion())) {
// same region
meta.locationBits = 3;
} else if (myLocation.getArea().equals(meta.location.getArea())) {
// same area
meta.locationBits = 1;
}
// keep the best server instance
if (max == null) {
max = meta;
} else if (meta.isBetterThan(
max, escapeAreaThreshold, escapeRegionThreshold, escapeAvailabilityThreshold)) {
max = meta;
}
}
if (max != null) {
if (metricRegistry != null) {
Counter counter = availabilityZoneToCounter.get(max.location.getAvailabilityZone());
if (counter == null) {
counter =
metricRegistry.counter(
name(serviceName, "az-requests", max.location.getAvailabilityZone()));
Counter prevCount =
availabilityZoneToCounter.putIfAbsent(max.location.getAvailabilityZone(), counter);
if (prevCount != null) {
// another thread snuck in their counter during a race condition so use it instead.
counter = prevCount;
}
}
counter.inc();
}
return max.server;
} else {
return null;
}
}