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="" xmlns:xsi="" xsi:schemaLocation=" http://www.springframework.org/schema/beans/spring-beans.xsd 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:${activemq.conf}/credentials.properties</value></property></bean><!–The <broker> element is used to configure the ActiveMQ broker.–><broker xmlns="" brokerName="broker129" dataDirectory="${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 inJMX. By default, ActiveMQ uses the MBean server that is started bythe JVM. For more information, see:–><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 persistencemechanism is the KahaDB store (identified by the kahaDB tag).For more information, see:–><persistenceAdapter><kahaDB directory="${activemq.data}/kahadb"/></persistenceAdapter><!–The systemUsage controls the maximum amount of space the broker willuse before disabling caching and/or slowing down producers. For more information, see:–><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 toclients and other brokers. For more information, see:–><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="" class="org.apache.activemq.hooks.SpringContextHook" /></shutdownHooks></broker><!–Enable web consoles, REST and Ajax APIs and demosThe web consoles requires by default login, you can disable this in the jetty.xml fileTake a look at ${ACTIVEMQ_HOME}/conf/jetty.xml for more details–><import resource="jetty.xml"/></beans>
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