Apache Camel - Throttler Hello World

Introduction

在設計web應用程式時，有時會需要一個節流器，去幫我控制單位時間內能處理的請求數量，以避免過載；又或者是要根據不同使用者所買的授權，去控制單位時間內能呼叫的API次數等。Camel提供了Throttler，讓我們能輕鬆透過設定，去達到這些效果。

我將透過HTTP GET請求/events/{id}做為範例，說明如何使用Throttler。首先介紹這個範例中的兩個RouteBuilder。

(程式碼可參考link)

RestRouteBuilder

REST核心設定集中在這個builder中，它負責宣告用什麼port與component去建立REST服務:

package org.tonylin.practice.camel.rest;
 
import org.apache.camel.builder.RouteBuilder;
import org.apache.camel.model.rest.RestBindingMode;
 
public class RestRouteBuilder extends RouteBuilder {	
 
	@Override
	public void configure() throws Exception {
		restConfiguration().component("netty4-http").port(8080).bindingMode(RestBindingMode.auto).endpointProperty("ssl",  "false");
	}
}

(我以http當範例，如果對https用法有興趣，可以參考這篇)

ThrottlerRouteBuilder

接下來是今天的主角，我先列出程式碼內容，後面再針對重點configure做說明:

package org.tonylin.practice.camel.throttler;
 
import static com.google.common.base.Preconditions.checkState;
 
import org.apache.camel.Exchange;
import org.apache.camel.Processor;
import org.apache.camel.builder.RouteBuilder;
import org.apache.camel.processor.ThrottlerRejectedExecutionException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
 
public class ThrottlerRouteBuilder extends RouteBuilder {
	private static Logger logger = LoggerFactory.getLogger(ThrottlerRouteBuilder.class);
	private final static String GET_EVENTS = "GET_EVENTS";
 
	private Object eventHandler;
 
	private int limit = 2;
	private int period = 200;
 
	public ThrottlerRouteBuilder(Object eventHandler) {
		this.eventHandler = eventHandler;
 
	}
 
	public void setLimit(int limit) {
		this.limit = limit;
	}
 
	public void setPeriod(int period) {
		this.period = period;
	}
 
	@Override
	public void configure() throws Exception {
		checkState(eventHandler!=null, "Can't find eventHandler");
 
		onException(ThrottlerRejectedExecutionException.class)
		.process(new Processor() {
			@Override
			public void process(Exchange exchange) throws Exception {
				logger.debug("handle ThrottlerRejectedExecutionException");
				exchange.getOut().setHeader(Exchange.HTTP_RESPONSE_CODE, "503");
			}
		})
		.handled(true);
 
		rest("/events/{id}").get().route().id(GET_EVENTS)
		.throttle(limit)
		.timePeriodMillis(period)
		.rejectExecution(true)
		.bean(eventHandler).endRest();
	}
}

我首要說明的是throttler的configure:

rest("/events/{id}").get().route().id(GET_EVENTS)
	.throttle(limit)
	.timePeriodMillis(period)
	.rejectExecution(true)
	.bean(eventHandler).endRest();

除了HTTP GET的宣告外，這些程式碼代表著以下意義:

throttle(limit): 限制的存取次數。
timePeriodMillis(period): 限制存取次數的單位時間，預設是1000ms。
rejectExecution(true): 當超過此限制時，是否要reject請求，預設為false。假如沒reject，後續超過限制的請求會block至單位時間後執行。
bean(eventHandler): 請求的處理者。

在我設定rejectExecution為true後，我發現camel會拋出ThrottlerRejectedExecutionException，且client會block住；因此這個設定必須與camel的errorHandler一同使用，這是我的使用範例:

onException(ThrottlerRejectedExecutionException.class)
	.process(new Processor() {
		@Override
		public void process(Exchange exchange) throws Exception {
			logger.debug("handle ThrottlerRejectedExecutionException");
			exchange.getOut().setHeader(Exchange.HTTP_RESPONSE_CODE, "503");
		}
	})
.handled(true);

我宣告當發生ThrottlerRejectedExecutionException例外時，會將回應給client的response code設為503以代表server過載。除此之外，別忘記把handled設為true，代表例外已被處理。

Unit Test

最後我以單元測試來展示效果，包含testOverload與testThrottlePeriod兩個測試；而throttler的limit為2，period為200ms，testcase會在後面做說明:

package org.tonylin.practice.camel.throttler;
 
import java.util.ArrayList;
import java.util.List;
 
import org.apache.camel.RoutesBuilder;
import org.apache.camel.test.junit4.CamelTestSupport;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClientBuilder;
import org.junit.Test;
import org.tonylin.practice.camel.rest.RestHandler;
import org.tonylin.practice.camel.rest.RestRouteBuilder;
 
public class ThrottlerRouteBuilderTest extends CamelTestSupport {
 
	private RestHandler hander = new RestHandler();
	private static final int limit = 2;
	private static final int period = 200;
 
	private HttpClient client = HttpClientBuilder.create().build();
	private HttpGet httpGet = new HttpGet("http://localhost:8080/events/123");
 
	@Override
	protected RoutesBuilder[] createRouteBuilders() throws Exception {
		ThrottlerRouteBuilder throttlerRouteBuilder = new ThrottlerRouteBuilder(hander);
		throttlerRouteBuilder.setLimit(limit);
		throttlerRouteBuilder.setPeriod(period);
 
		return new RoutesBuilder[] {
				new RestRouteBuilder(),
				throttlerRouteBuilder
		};
	}
 
	private List<HttpResponse> batchRequest(int times) throws Exception {
		List<HttpResponse> responses = new ArrayList<HttpResponse>();
		for( int i = 0 ; i < times ; i++ ) {
			responses.add(client.execute(httpGet));
		}
		return responses;
	}
 
	@Test
	public void testOverload() throws Exception {
		// skip
	}
 
	@Test
	public void testThrottlePeriod() throws Exception  {
		// skip
	}
}

測試中使用的RestHandler，負責收集請求的event id，用以確認請求內容是否正確:

public class RestHandler {
	private static Logger logger = LoggerFactory.getLogger(RestHandler.class);
	private List<String> requestIds = new ArrayList<String>();
 
	@Handler
	public void handle(Exchange exchange) {
		String requestId = exchange.getIn().getHeader("id", String.class);
		logger.debug("Request id: {}", requestId);
		requestIds.add(requestId);
	}
 
	public List<String> getRequestIds(){
		return requestIds;
	}
}

針對testOverload測試，是用來確認throttler單位時間內的請求是否有效；因此測試中，連續做了3次請求，最後會去確認這三次的請求結果是否正確:

@Test
public void testOverload() throws Exception {
	// when request 3 times
	List<HttpResponse> responses = batchRequest(3);
 
	// then
	assertEquals(2, hander.getRequestIds().size());
	assertEquals(200, responses.get(0).getStatusLine().getStatusCode());
	assertEquals(200, responses.get(1).getStatusLine().getStatusCode());
	assertEquals(503, responses.get(2).getStatusLine().getStatusCode());
}

而testThrottlePeriod測試，用以確認throttler單位時間是否有作用；因此測試中，會先發3次請求，再等待此單位時間後，再發3次請求。最後確認請求結果:

@Test
public void testThrottlePeriod() throws Exception  {
	// when
	List<HttpResponse> responses = batchRequest(3);
	Thread.sleep(period+1);
 
	responses.addAll(batchRequest(3));
 
	// then
	assertEquals(2, hander.getRequestIds().size());
	assertEquals(200, responses.get(0).getStatusLine().getStatusCode());
	assertEquals(200, responses.get(1).getStatusLine().getStatusCode());
	assertEquals(503, responses.get(2).getStatusLine().getStatusCode());
	assertEquals(200, responses.get(3).getStatusLine().getStatusCode());
	assertEquals(200, responses.get(4).getStatusLine().getStatusCode());
	assertEquals(503, responses.get(5).getStatusLine().getStatusCode());
}

透過這兩個測試範例，我們可以簡單地了解throttler的用法。

Library Info (Gradle Config)

以下是我在寫這篇文章時，所使用的libraries版本:

ext {
	camelVersion='2.23.1'
	nettyAllVersion='4.1.34.Final'
	guavaVersion='27.1-jre'
	log4jVersion='1.2.17'
	slf4jVersion='1.7.26'
	httpClientVersion='4.5.7'
}

dependencies {
    compile group: 'org.apache.camel', name: 'camel-core', version: "$camelVersion"
    compile group: 'org.apache.camel', name: 'camel-netty4-http', version: "$camelVersion"
    compile group: 'org.apache.camel', name: 'camel-http-common', version: "$camelVersion"
    compile group: 'org.apache.camel', name: 'camel-netty4', version: "$camelVersion"
    compile group: 'io.netty', name: 'netty-all', version: "$nettyAllVersion"
    compile group: 'com.google.guava', name: 'guava', version: "$guavaVersion"
    compile group: 'log4j', name: 'log4j', version: "$log4jVersion"
    compile group: 'org.slf4j', name: 'slf4j-api', version: "$slf4jVersion"
    runtime group: 'org.slf4j', name: 'slf4j-log4j12', version: "$slf4jVersion"
    testCompile group: 'org.apache.camel', name: 'camel-test', version: "$camelVersion"
    testCompile group: 'org.apache.httpcomponents', name: 'httpclient', version: "$httpClientVersion"
    testCompile 'junit:junit:4.12'
}

Reference

Camel - Throttler

阿兩的筆記本 Ryoutsu's Notebook

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