Good use of bridged MQTT brokers - activemq

Question

I'm currently working on a project on which an external app sends data coming from many sensors via MQTT protocol.
I want to collect all of this data, and I want to send them to an external server. I want to create 2 MQTT brokers:
one local (on the machine with the app that sends data)
one in the distant server
I will create a network bridge between the two. It's a possibility given by my MQTT server app ActiveMQ (I imagine that's a common feature).
In this way the data producing app will publish on the local broker and, via the bridge, the same data will be published on the remote broker. The point is to let the app working without problems in case of connection loss.
When I lose the network connection between the brokers I don't get the data produced by the app during the time there were no connection. Do you know if it's possible to configure the bridge in order to make it work the way I want?
Will I have to develop a little program which listens on all topics from the local broker, detects connection losses, and re-sends all lost messages to the remote broker?
I add configuration files from my two brokers. My first ActiveMQ server is on the same machine as my app and the second ActiveMQ server is on another machine on the same network. Both computers ping each other perfectly.
Local broker:
<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">
<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<property name="locations">
<value>file:${activemq.conf}/credentials.properties</value>
</property>
</bean>
<bean id="logQuery" class="io.fabric8.insight.log.log4j.Log4jLogQuery"
lazy-init="false" scope="singleton"
init-method="start" destroy-method="stop">
</bean>
<broker xmlns="http://activemq.apache.org/schema/core" brokerName="localhost" dataDirectory="${activemq.data}">
<destinationPolicy>
<policyMap>
<policyEntries>
<policyEntry topic=">" >
<pendingMessageLimitStrategy>
<constantPendingMessageLimitStrategy limit="1000"/>
</pendingMessageLimitStrategy>
</policyEntry>
</policyEntries>
</policyMap>
</destinationPolicy>
<managementContext>
<managementContext createConnector="false"/>
</managementContext>
<persistenceAdapter>
<kahaDB directory="${activemq.data}/kahadb"/>
</persistenceAdapter>
<systemUsage>
<systemUsage>
<memoryUsage>
<memoryUsage percentOfJvmHeap="70" />
</memoryUsage>
<storeUsage>
<storeUsage limit="100 gb"/>
</storeUsage>
<tempUsage>
<tempUsage limit="50 gb"/>
</tempUsage>
</systemUsage>
</systemUsage>
<transportConnectors>
<transportConnector name="mqtt" uri="mqtt://0.0.0.0:1883?maximumConnections=1000&wireFormat.maxFrameSize=104857600"/>
</transportConnectors>
<networkConnectors>
<networkConnector uri="static:(tcp://192.168.16.100:61616)"/>
</networkConnectors>
<shutdownHooks>
<bean xmlns="http://www.springframework.org/schema/beans" class="org.apache.activemq.hooks.SpringContextHook" />
</shutdownHooks>
</broker>
<import resource="jetty.xml"/>
</beans>
Remote broker:
<beans
xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://activemq.apache.org/schema/core http://activemq.apache.org/schema/core/activemq-core.xsd">
<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<property name="locations">
<value>file:${activemq.conf}/credentials.properties</value>
</property>
</bean>
<bean id="logQuery" class="io.fabric8.insight.log.log4j.Log4jLogQuery"
lazy-init="false" scope="singleton"
init-method="start" destroy-method="stop">
</bean>
<broker xmlns="http://activemq.apache.org/schema/core" brokerName="localhost" dataDirectory="${activemq.data}">
<destinationPolicy>
<policyMap>
<policyEntries>
<policyEntry topic=">" >
<pendingMessageLimitStrategy>
<constantPendingMessageLimitStrategy limit="1000"/>
</pendingMessageLimitStrategy>
</policyEntry>
</policyEntries>
</policyMap>
</destinationPolicy>
<managementContext>
<managementContext createConnector="false"/>
</managementContext>
<persistenceAdapter>
<kahaDB directory="${activemq.data}/kahadb"/>
</persistenceAdapter>
<systemUsage>
<systemUsage>
<memoryUsage>
<memoryUsage percentOfJvmHeap="70" />
</memoryUsage>
<storeUsage>
<storeUsage limit="100 gb"/>
</storeUsage>
<tempUsage>
<tempUsage limit="50 gb"/>
</tempUsage>
</systemUsage>
</systemUsage>
<transportConnectors>
<transportConnector name="openwire" uri="tcp://0.0.0.0:61616?maximumConnections=1000&wireFormat.maxFrameSize=104857600"/>
<transportConnector name="mqtt" uri="mqtt://0.0.0.0:1883?maximumConnections=1000&wireFormat.maxFrameSize=104857600"/>
</transportConnectors>
<shutdownHooks>
<bean xmlns="http://www.springframework.org/schema/beans" class="org.apache.activemq.hooks.SpringContextHook" />
</shutdownHooks>
</broker>
<import resource="jetty.xml"/>
</beans>
In order to simulate disconnection between the two brokers I simply disconnects the second computer from the network.
I use MQTTBox on both computer to subscribe to topics I write on. That's how I saw that data sent on a topic in the local broker during the disconnection of the second computer is not published on the same topic of the remote broker when I reconnect it.
EDIT : new infos
I tried again my test today and I notice a checkbox "retain" on my MQTT client MQTTBox.
So :
With the computer A, I publish a message with retain checked on topic /test and computer B was listening on /#
When the 2 computers are connected, it obviously works well, I see the message on computer B.
When I disconnect computer B, publish 2 messages with retain checked then reconnect computer B, I only see the most recent of the 2 messages I published...
It's better, but I'd like to see the other message too... If anyone can help me, i'm lost...
I can also set a QoS for the message I want to publish. I tried with Qos = 0 and QoS = 1 : same thing.

Answer 1

QOS for messages works for bridge connections as well.
So if the bridge is configured for a topic with a QOS greater than 0 then the local broker will queue up the messages while the connection to the remote broker is down and will send them when the connection comes back up.
This way no messages will be lost.
This is perfectly normal deployment pattern for MQTT brokers.