ActiveMq master/slave

在一个网络内运行多个brokers或者stand alone brokers时存在一个问题，这就是消息在物理上只被一个broker持有，因此当某个broker失效，那么你只能等待直到它重启后，这个broker上的消息才能够被继续发送（如果没有设置持久化，那么在这种情况下，消息将会丢失）。Master Slave 背后的想法是，消息被复制到slave broker，因此即使master broker遇到了像硬件故障之类的错误，你也可以立即切换到slave broker而不丢失任何消息。

接下来介如何配置

解压两份activemq于不同的目录，其中一个broker命名为master，一个为slave

1. master端不做处理

2. slave： activemq.xml中配置如下

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<!-- START SNIPPET: example -->
<beans
  xmlns="http://www.springframework.org/schema/beans"
  xmlns:amq="http://activemq.apache.org/schema/core"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
  http://activemq.apache.org/schema/core http://activemq.apache.org/schema/core/activemq-core.xsd">

    <!-- Allows us to use system properties as variables in this configuration file -->
    <bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="locations">
            <value>file:${activemq.base}/conf/credentials.properties</value>
        </property>      
    </bean>

<broker brokerName="slave" useJmx="false"  deleteAllMessagesOnStartup="true"  xmlns="http://activemq.apache.org/schema/core">

  <services>
    <masterConnector remoteURI= "tcp://0.0.0.0:61616" userName="user" password="password"/>
  </services>

  <transportConnectors>
    <transportConnector uri="tcp://0.0.0.0:61617"/>
  </transportConnectors>
  
</broker>
    <!-- 
        Enable web consoles, REST and Ajax APIs and demos
        It also includes Camel (with its web console), see ${ACTIVEMQ_HOME}/conf/camel.xml for more info
        
        Take a look at ${ACTIVEMQ_HOME}/conf/jetty.xml for more details 
    -->
    <import resource="jetty.xml"/>
    
</beans>
<!-- END SNIPPET: example -->

3. java代码：

		ConnectionFactory connectionFactory = new ActiveMQConnectionFactory(
				"system",
				"manager", "failover:(tcp://0.0.0.0:61616,tcp://0.0.0.0:61617)");
		// JMS 客户端到JMS Provider 的连接
		Connection connection = connectionFactory.createConnection();
		connection.start();

启动slave后，master 会打印 active slave broker slave is attached

当关闭master 后，slave控制台会打印： Connector tcp://0.0.0.0:61617 Started

OK!

注：

1. slave将会在启动的时候去连接master，所以要先启动master

2. 除非master失效， 否则slave不会进行任何的传输或者是连接。

3. slave端 的broker  可以配置 一个额外的参数  shutdownOnMasterFailure, 设为true的话会在master失效的时候自动关闭

4.master端的参数： waitForslave： 设为true的意义  当master失效的时候，在slave工作之前，不允许有任何客户端或网络的连接

                                     shutdownOnSlaveFailure :  if ture ,the master will shutdown  if a slave becomes detached. This ensures that a  slave  is only  ever  in sync with the master