Throttling
Propósito
Garantizar que un cliente determinado no pueda acceder a los recursos del servicio más allá del límite asignado.
Explicación
Ejemplo del mundo real
Un joven humano y un viejo enano entran en un bar. Empiezan a pedir cervezas al camarero.
El camarero se da cuenta inmediatamente de que el joven humano no debe consumir demasiadas bebidas demasiado rápido
y se niega a servir si no ha pasado suficiente tiempo. Para el viejo enano, el ritmo de servicio puede ser mayor.
ser mayor.
En palabras sencillas
El patrón de Throttling se utiliza para limitar la velocidad de acceso a un recurso.
Controlar el consumo de recursos utilizados por una instancia de una aplicación, un tenant individual,
o un servicio completo. Esto puede permitir que el sistema continúe funcionando y cumpla con los acuerdos de nivel de servicio, incluso cuando un aumento de la demanda impone una carga extrema sobre los recursos.
Ejemplo programático
La clase BarCustomer presenta los clientes de la API Bartender. La clase CallsCount registra el número de
llamadas por BarCustomer.
public class BarCustomer {
@Getter
private final String name;
@Getter
private final int allowedCallsPerSecond;
public BarCustomer(String name, int allowedCallsPerSecond, CallsCount callsCount) {
if (allowedCallsPerSecond < 0) {
throw new InvalidParameterException("Number of calls less than 0 not allowed");
}
this.name = name;
this.allowedCallsPerSecond = allowedCallsPerSecond;
callsCount.addTenant(name);
}
}
@Slf4j
public final class CallsCount {
private final Map<String, AtomicLong> tenantCallsCount = new ConcurrentHashMap<>();
public void addTenant(String tenantName) {
tenantCallsCount.putIfAbsent(tenantName, new AtomicLong(0));
}
public void incrementCount(String tenantName) {
tenantCallsCount.get(tenantName).incrementAndGet();
}
public long getCount(String tenantName) {
return tenantCallsCount.get(tenantName).get();
}
public void reset() {
tenantCallsCount.replaceAll((k, v) -> new AtomicLong(0));
LOGGER.info("reset counters");
}
}
A continuación, se introduce el servicio al que llaman los inquilinos. Para realizar un seguimiento del número de llamadas, se utiliza un temporizador de estrangulamiento.
public interface Throttler {
void start();
}
public class ThrottleTimerImpl implements Throttler {
private final int throttlePeriod;
private final CallsCount callsCount;
public ThrottleTimerImpl(int throttlePeriod, CallsCount callsCount) {
this.throttlePeriod = throttlePeriod;
this.callsCount = callsCount;
}
@Override
public void start() {
new Timer(true).schedule(new TimerTask() {
@Override
public void run() {
callsCount.reset();
}
}, 0, throttlePeriod);
}
}
El Bartender ofrece el servicio orderDrink a los BarCustomers. Los clientes probablemente no
saben que la tasa de servicio de cerveza está limitada por su apariencia.
class Bartender {
private static final Logger LOGGER = LoggerFactory.getLogger(Bartender.class);
private final CallsCount callsCount;
public Bartender(Throttler timer, CallsCount callsCount) {
this.callsCount = callsCount;
timer.start();
}
public int orderDrink(BarCustomer barCustomer) {
var tenantName = barCustomer.getName();
var count = callsCount.getCount(tenantName);
if (count >= barCustomer.getAllowedCallsPerSecond()) {
LOGGER.error("I'm sorry {}, you've had enough for today!", tenantName);
return -1;
}
callsCount.incrementCount(tenantName);
LOGGER.debug("Serving beer to {} : [{} consumed] ", barCustomer.getName(), count+1);
return getRandomCustomerId();
}
private int getRandomCustomerId() {
return ThreadLocalRandom.current().nextInt(1, 10000);
}
}
Ahora es posible ver el ejemplo completo en acción. BarCustomer` el joven humano está limitado a 2
llamadas por segundo y el viejo enano a 4.
public static void main(String[] args) {
var callsCount = new CallsCount();
var human = new BarCustomer("young human", 2, callsCount);
var dwarf = new BarCustomer("dwarf soldier", 4, callsCount);
var executorService = Executors.newFixedThreadPool(2);
executorService.execute(() -> makeServiceCalls(human, callsCount));
executorService.execute(() -> makeServiceCalls(dwarf, callsCount));
executorService.shutdown();
try {
executorService.awaitTermination(10, TimeUnit.SECONDS);
} catch (InterruptedException e) {
LOGGER.error("Executor service terminated: {}", e.getMessage());
}
}
private static void makeServiceCalls(BarCustomer barCustomer, CallsCount callsCount) {
var timer = new ThrottleTimerImpl(1000, callsCount);
var service = new Bartender(timer, callsCount);
// Sleep is introduced to keep the output in check and easy to view and analyze the results.
IntStream.range(0, 50).forEach(i -> {
service.orderDrink(barCustomer);
try {
Thread.sleep(100);
} catch (InterruptedException e) {
LOGGER.error("Thread interrupted: {}", e.getMessage());
}
});
}
Un extracto de la salida de consola del ejemplo:
18:46:36.218 [Timer-0] INFO com.iluwatar.throttling.CallsCount - reset counters
18:46:36.218 [Timer-1] INFO com.iluwatar.throttling.CallsCount - reset counters
18:46:36.242 [pool-1-thread-2] DEBUG com.iluwatar.throttling.Bartender - Serving beer to dwarf soldier : [1 consumed]
18:46:36.242 [pool-1-thread-1] DEBUG com.iluwatar.throttling.Bartender - Serving beer to young human : [1 consumed]
18:46:36.342 [pool-1-thread-2] DEBUG com.iluwatar.throttling.Bartender - Serving beer to dwarf soldier : [2 consumed]
18:46:36.342 [pool-1-thread-1] DEBUG com.iluwatar.throttling.Bartender - Serving beer to young human : [2 consumed]
18:46:36.443 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
18:46:36.443 [pool-1-thread-2] DEBUG com.iluwatar.throttling.Bartender - Serving beer to dwarf soldier : [3 consumed]
18:46:36.544 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
18:46:36.544 [pool-1-thread-2] DEBUG com.iluwatar.throttling.Bartender - Serving beer to dwarf soldier : [4 consumed]
18:46:36.645 [pool-1-thread-2] ERROR com.iluwatar.throttling.Bartender - I'm sorry dwarf soldier, you've had enough for today!
18:46:36.645 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
18:46:36.745 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
18:46:36.745 [pool-1-thread-2] ERROR com.iluwatar.throttling.Bartender - I'm sorry dwarf soldier, you've had enough for today!
18:46:36.846 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
18:46:36.846 [pool-1-thread-2] ERROR com.iluwatar.throttling.Bartender - I'm sorry dwarf soldier, you've had enough for today!
18:46:36.947 [pool-1-thread-2] ERROR com.iluwatar.throttling.Bartender - I'm sorry dwarf soldier, you've had enough for today!
18:46:36.947 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
18:46:37.048 [pool-1-thread-2] ERROR com.iluwatar.throttling.Bartender - I'm sorry dwarf soldier, you've had enough for today!
18:46:37.048 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
18:46:37.148 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
18:46:37.148 [pool-1-thread-2] ERROR com.iluwatar.throttling.Bartender - I'm sorry dwarf soldier, you've had enough for today!
Diagrama de clases
Aplicabilidad
El patrón Throttling debe utilizarse:
- Cuando se necesita restringir el acceso al servicio para no tener un alto impacto en el rendimiento del mismo.
- Cuando varios clientes consumen los mismos recursos del servicio y la restricción debe hacerse en función del uso por cliente.