再谈Apache ActiveMQ 负载均衡

前面文章《Apache ActiveMQ 负载均衡》在最后有提到一个场景，就是当AMQ的节点数大于2个的时候（HA + LB），且配置了消息回流的情况下的一些问题。

HA + LB的基本结构如下图：

问题即发生在当生产者将消息投递到Master节点后（AMQ SERVER），消费者与A节点建立连接（Broker），根据AMQ的“预先消费”策略预先消费了一定数量的消息，即A节点消费了Master节点的一部分消息，A节点在将消息转发至消费者Consumer。

消费者在消费过程中，A节点意外宕机，消费者根据failover机制会自动连接至B或C节点，想继续消费剩余的消息（A节点未消费完成的消息）。

那么我们可以按如下的配置方式即可解决该场景下的问题：

<beans
  xmlns="http://www.springframework.org/schema/beans"
  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.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.conf}/credentials.properties</value>
        </property>
    </bean>

    <!--
        The <broker> element is used to configure the ActiveMQ broker.
    -->
    <broker xmlns="http://activemq.apache.org/schema/core" brokerName="broker129" dataDirectory="${activemq.data}">

<!-- Destination specific policies using destination names or wildcards -->
        <destinationPolicy>
            <policyMap>
                <policyEntries>
                    <policyEntry topic=">">
                    </policyEntry>
                    <policyEntry queue=">" enableAudit="false">
                        <deadLetterStrategy>
                                <individualDeadLetterStrategy queuePrefix="DLQ." useQueueForQueueMessages="true" />                                     
                                                        </deadLetterStrategy>
                        <networkBridgeFilterFactory>
                                <conditionalNetworkBridgeFilterFactory replayWhenNoConsumers="true"/>
                        </networkBridgeFilterFactory>
                    </policyEntry>
                </policyEntries>
            </policyMap>
        </destinationPolicy>

        <!--
            The managementContext is used to configure how ActiveMQ is exposed in
            JMX. By default, ActiveMQ uses the MBean server that is started by
            the JVM. For more information, see:

            http://activemq.apache.org/jmx.html
        -->
        <managementContext>
            <managementContext createConnector="false"/>
        </managementContext>

<!-- 
duplex Broker双工模式，即：Broker可以是消费者也可以是发布者。
该参数同“消息回流”（replayWhenNoConsumers）不同，注意区分。
 -->
<!-- networkTTL 即：信息和订阅在网络可以通过的Broker数量。该参数需要根据LB数量合理设置 -->
        <networkConnectors>
            <networkConnector duplex="true" networkTTL="3"  uri="static:(tcp://192.168.137.200:61616)"/>
        </networkConnectors>

        <!--
            Configure message persistence for the broker. The default persistence
            mechanism is the KahaDB store (identified by the kahaDB tag).
            For more information, see:

            http://activemq.apache.org/persistence.html
        -->
        <persistenceAdapter>
            <kahaDB directory="${activemq.data}/kahadb"/>
        </persistenceAdapter>


          <!--
            The systemUsage controls the maximum amount of space the broker will
            use before disabling caching and/or slowing down producers. For more information, see:
            http://activemq.apache.org/producer-flow-control.html
          -->
          <systemUsage>
            <systemUsage>
                <memoryUsage>
                    <memoryUsage percentOfJvmHeap="70" />
                </memoryUsage>
                <storeUsage>
                    <storeUsage limit="100 gb"/>
                </storeUsage>
                <tempUsage>
                    <tempUsage limit="50 gb"/>
                </tempUsage>
            </systemUsage>
        </systemUsage>

        <!--
            The transport connectors expose ActiveMQ over a given protocol to
            clients and other brokers. For more information, see:

            http://activemq.apache.org/configuring-transports.html
        -->
        <transportConnectors>
            <!-- DOS protection, limit concurrent connections to 1000 and frame size to 100MB -->
            <transportConnector name="openwire" uri="nio://0.0.0.0:61616?maximumConnections=1000&wireFormat.maxFrameSize=104857600"/>
        </transportConnectors>

        <!-- destroy the spring context on shutdown to stop jetty -->
        <shutdownHooks>
            <bean xmlns="http://www.springframework.org/schema/beans" class="org.apache.activemq.hooks.SpringContextHook" />
        </shutdownHooks>

    </broker>

    <!--
        Enable web consoles, REST and Ajax APIs and demos
        The web consoles requires by default login, you can disable this in the jetty.xml file

        Take a look at ${ACTIVEMQ_HOME}/conf/jetty.xml for more details
    -->
    <import resource="jetty.xml"/>

</beans>