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Flume 实战(2)--Flume-ng-sdk源码分析
具体参考: 官方用户手册和开发指南
http://flume.apache.org/FlumeDeveloperGuide.html
*) 定位和简单例子
1). Flume-ng-sdk是用于编写往flume agent发送数据的client sdk
2). 简单示例
RpcClient client = null;try { client = RpcClientFactory.getDefaultInstance("127.0.0.1", 41414); Event event = EventBuilder.withBody("hello flume", Charset.forName("UTF-8")); client.append(event);} catch (EventDeliveryException e) { e.printStackTrace();} finally { if ( client != null ) { client.close(); }}*) Event设计和类层次结构
1. Event类设计
在Flume中Event是个接口类
public interface Event { public Map<String, String> getHeaders(); public void setHeaders(Map<String, String> headers); public byte[] getBody(); public void setBody(byte[] body);}由代码可得, Event由Header集合和消息负载两部分构成.
2. Builder设计模式
在org.apache.flume.event下, 有两个Event的具体实现类: SimpleEvent, JSonEvent.
EventBuilder类顾名思义, 采用Builder的方式来组装对象的成员, 并产生最终的对象.
public class EventBuilder { public static Event withBody(byte[] body, Map<String, String> headers) { Event event = new SimpleEvent(); if(body == null) { body = new byte[0]; } event.setBody(body); if (headers != null) { event.setHeaders(new HashMap<String, String>(headers)); } return event; } public static Event withBody(byte[] body) { return withBody(body, null); } public static Event withBody(String body, Charset charset, Map<String, String> headers) { return withBody(body.getBytes(charset), headers); } public static Event withBody(String body, Charset charset) { return withBody(body, charset, null); }}java的访问控制符: public/default/protected/private, default表示同package可见
不过另人意外的是, 其对应的SimpleEvent的构造函数的修饰符是public, 即不是default, 也不是protected, 这点让EventBuilder的引入有些失败.把Builder模式, 用到极致的是Google Protocol Buffer(java), 其每个PB对象, 都是用相应的Builder类来组装和生成. 采用这种Builder模式的用途是, 把一个对象元素的修改和读取彻底分离, 使得一个PB对象,从诞生后就是一个immutable对象, 只能读取其属性信息, 而不能修改其属性.
*) RpcClient设计和类层次结构
1. RpcClient的接口定义:
public interface RpcClient { public int getBatchSize(); public void append(Event event) throws EventDeliveryException; public void appendBatch(List<Event> events) throws EventDeliveryException; public boolean isActive(); public void close() throws FlumeException;}2. AbstractRpcClient的抽象类定义:
public abstract class AbstractRpcClient implements RpcClient { protected int batchSize = RpcClientConfigurationConstants.DEFAULT_BATCH_SIZE; protected long connectTimeout = RpcClientConfigurationConstants.DEFAULT_CONNECT_TIMEOUT_MILLIS; protected long requestTimeout = RpcClientConfigurationConstants.DEFAULT_REQUEST_TIMEOUT_MILLIS; @Override public int getBatchSize(){ return batchSize; } protected abstract void configure(Properties properties) throws FlumeException;}新增了一些常量定义, 和新的抽象函数configure(Properties prop);
3. RpcClient工厂类的使用
RpcClientFactory的定义
public class RpcClientFactory { public static RpcClient getInstance(Properties properties) throws FlumeException { // 1). 获取具体rpcclient的类型信息 properties.getProperty(RpcClientConfigurationConstants.CONFIG_CLIENT_TYPE); // 2). 利用反射,获取类的class Class<? extends AbstractRpcClient> clazz = (Class<? extends AbstractRpcClient>) Class.forName(...); // 3). 产生类对象 RpcClient client = clazz.newInstance(); // 4). 进行具体rpcclient实例的配置初始化 client.configure(properties); // 5). 返回对象 return client; }}RpcClientFactory借助静态方法getInstance, 其依据Properties里的相应key/value来, 来产生不同的对象实例, 配置不同的属性. 同时RpcClient的具体实例, 其构造方法的访问限定符都是protected, 这一点做的, 比之前EventBuilder设计和实现要规范和清晰.
clazz = Class.forName(...);client = class.newInstance();client.configure(...);
是种非常好的实践代码, 把面向对象的多态性用到极致
4. 具体的RpcClient类的实现
其SDK提供了两大类, 具体的实现类ThriftRpcClient和AvroRpcClient
4.1. 对ThriftRpcClient的解读
4.1.1 thrift idl的定义
idl文件(src/main/thrift/flume.thrift)的定义
namespace java org.apache.flume.thriftstruct ThriftFlumeEvent { 1: required map <string, string> headers, 2: required binary body,}enum Status { OK, FAILED, ERROR, UNKNOWN}service ThriftSourceProtocol { Status append(1: ThriftFlumeEvent event), Status appendBatch(1: list<ThriftFlumeEvent> events),}分别对应源码包org.apache.flume.thrift下
Status, ThriftFlumeEvent, ThriftSourceProtocol类
4.1.2 ThriftRpcClient的实现
ThriftRpcClient并不是简单对ThriftSourceProtocol的客户端的简单封装
public class ThriftRpcClient extends AbstractRpcClient { private ConnectionPoolManager connectionManager; private final ExecutorService callTimeoutPool; private final AtomicLong threadCounter; // ......}评注: 粗略观察其类成员, 其借助线程池(ExecutorService)和连接池(ConnectionManager)管理, 来实现RpcClient的发送接口, 这样append(), appendBatch()的接口都是线程安全的, 该客户端的实例能用于多线程并发使用.
AvroRpcClient代码结构差不多, 先一笔带过.
5. 两个重要的实现类
FailOverRpcClient的源码解析:
这边采用装饰模式(Decorator Pattern), FailOverRpcClient继承自RpcClient, 同时又拥有实际的RpcClient实例, 只是在实际RpcClient基础上, 添加了失败后重试的能力.
FailOver是失败后重试的机制, 通常借助带尝试次数的重试来实现
其append(Event e)方法中:
int tries = 0;while (tries < maxTries) { try { tries++; localClient = getClient(); localClient.append(event); return; } catch (EventDeliveryException e) { localClient.close(); localClient = null; } catch (Exception e2) { throw new EventDeliveryException( "Failed to send event. Exception follows: ", e2); }} 这段代码采用相对简单的.
getNextClient()的实现如下:
for (int count = lastCheckedhost + 1; count < limit; count++) { HostInfo hostInfo = hosts.get(count); try { setDefaultProperties(hostInfo, props); localClient = RpcClientFactory.getInstance(props); lastCheckedhost = count; return localClient; } catch (FlumeException e) { logger.info("Could not connect to " + hostInfo, e); continue; }}for(int count = 0; count <= lastCheckedhost; count++) { HostInfo hostInfo = hosts.get(count); try { setDefaultProperties(hostInfo, props); localClient = RpcClientFactory.getInstance(props); lastCheckedhost = count; return localClient; } catch (FlumeException e) { logger.info("Could not connect to " + hostInfo, e); continue; }}HostInfo封装了一个远端服务的ip地址
FailOver简单的轮询了各个服务地址.
LoadBalancingRpcClient的源码解析:
LoadBalancingRpcClient顾名思义, 采用负载均衡的策略来实现, 其还是采用遍历(轮询/随机)+反馈的机制, 来动态的调整服务列表的候选顺序.
在append(Event)方法中:
Iterator<HostInfo> it = selector.createHostIterator();while (it.hasNext()) { HostInfo host = it.next(); try { RpcClient client = getClient(host); client.append(event); eventSent = true; break; } catch (Exception ex) { selector.informFailure(host); LOGGER.warn("Failed to send event to host " + host, ex); }}if (!eventSent) { throw new EventDeliveryException("Unable to send event to any host");}selector.createHostIterator() 创建当前服务候选列表的一个快照, 同时递进一个轮询单元.
selector.informFailure(host) 是对失败的服务进行降级处理
而HostSelector接口定义如下:
public interface HostSelector { void setHosts(List<HostInfo> hosts); Iterator<HostInfo> createHostIterator(); void informFailure(HostInfo failedHost);}其具体实现类
#). RoundRobinHostSelector, 借助轮询的方式来实现
#). RandomOrderHostSelector, 借助随机的方式来实现
这两个类, 都是借助OrderSelector<T>的实现类来实现, OrderSelector封装了对错误服务机器列表的屏蔽策略
该屏蔽策略如下所示:
失败一次, 设置一个恢复时间点, 未到该恢复时间点, 则不允许获取该机器ip/port
同时为了惩罚多次失败, 减少获取该服务机器的ip/port, 采用1000 * (1 << sequentialFails), 连续失败次数, 其恢复时间的间隔要加大.
*) Properties的属性配置
基本的属性配置
client.type = default (for avro) or thrift (for thrift)hosts = h1 # default client accepts only 1 hosthosts.h1 = host1.example.org:41414 # host and port must both be specifiedbatch-size = 100 # Must be >=1 (default: 100)connect-timeout = 20000 # Must be >=1000 (default: 20000)request-timeout = 20000 # Must be >=1000 (default: 20000)
FailOver支持的配置
client.type = default_failoverhosts = h1 h2 h3 # at least one is required, but 2 or more makes better sensemax-attempts = 3 # Must be >=0 (default: number of hosts
Balancing支持的配置
client.type = default_loadbalancehosts = h1 h2 h3 # At least 2 hosts are requiredbackoff = false # Specifies whether the client should back-off from a failed hostmaxBackoff = 0 # Max timeout in millis host-selector = round_robin # The host selection strategy used
*) 异常类定义
EventDeliveryException和FlumeException