Why does this ActiveMQ broker configuration fail after many brokers are added? - activemq

Question

Software and configurations:
ActiveMQ 5.14.0, Java 8
All brokers have non-persistent topics only; advisory messages are on.
OS: Linux (RHEL 6)
Some terminology:
We have headless Java applications (services) that use a broker to communicate with the web server. They use Java Plugin Framework (JPF). Each service connects to its own personal broker and subscribes to a single topic that is unique to that service (a "service-specific" topic).
This broker has a network connector that automatically connects to all local web instance brokers (typically only 1 of them per LAN).
This broker has a network connector that automatically connects to all local root borker instances (typically only 1 of them per LAN).
Only the web servers ever publish messages to this topic.
Services don't send messages intended for one another.
The web server acts as a front end for the services. It uses Spring Boot. Each web server connects to its own personal broker and subscribes to a single global topic that is shared among all web servers; if a message is sent to that topic, all web servers receive it.
Only the services ever publish messages to this topic.
Web servers don't send messages intended for one another.
This broker has a network connector that automatically connects to all local root borker instances (typically only 1 of them per LAN).
The root broker is a glorified Java appliction that launches an ActiveMQ broker. It uses Spring Boot. The root brokers don't publish or subscribe; they merely act as a bridge between LANs.
Each root broker will connect to its parent broker (not done via XML). This is done in Java code.
Settings: duplex=true, checkDuplicateMessagesOnDuplex=true, suppressDuplicateTopicSubscriptions=false, networkTTL=10
I followed this guide in configuring all of the brokers: http://activemq.apache.org/networks-of-brokers.html
Here's a diagram of the intended architecture:
What we're observing is that after a certain number of services come online, messages stop flowing between the service and web application instances, even if they're on the same LAN and directly connected to one another. We can see the producers creating the messages (in the web application logs), but the consumers never receive the network data (verified using Wireshark). I can't tell if the the brokers are sending the messages to the wrong location or not. The correct topics show up in our JMX MBEANS when we view a running instance using jconsole.
There are no errors/warnings from any of the JVMs.
One observation we've made is that adding a new web server and service in a different discovery group appears to work with no problem. They have no communication issues whatsoever, so we believe this is a broker configuration issue.
service-broker.xml:
<!-- Connects to root broker and web broker -->
<networkConnectors>
<networkConnector name="service-${broker.id}-broker-nc" duplex="true" networkTTL="10"
checkDuplicateMessagesOnDuplex="true" suppressDuplicateTopicSubscriptions="false"
uri="multicast://225.5.5.5:6555?group=GROUP_BROKER&maxReconnectAttempts=1&joinNetworkInterface=${broker.netInterface}" />
<networkConnector name="service-${broker.id}-web-nc" duplex="true" networkTTL="10"
checkDuplicateMessagesOnDuplex="true" suppressDuplicateTopicSubscriptions="false"
uri="multicast://225.5.5.5:6555?group=GROUP_WEB&maxReconnectAttempts=1&joinNetworkInterface=${broker.netInterface}" />
</networkConnectors>
<!-- Don't advertise the broker (only connection should be from localhost) -->
<transportConnectors>
<transportConnector name="openwire"
uri="tcp://${broker.ip}:${broker.port}?maximumConnections=1000&wireFormat.maxFrameSize=104857600" />
</transportConnectors>
web-broker.xml:
<!-- Connect to root broker -->
<networkConnectors>
<networkConnector name="web-${broker.id}-broker-nc" duplex="true" networkTTL="10"
checkDuplicateMessagesOnDuplex="true" suppressDuplicateTopicSubscriptions="false"
uri="multicast://225.5.5.5:6555?group=GROUP_BROKER&maxReconnectAttempts=1" />
</networkConnectors>
<!-- Advertise web broker (service will connect to this) -->
<transportConnectors>
<transportConnector name="openwire"
uri="tcp://${broker.ip}:${broker.port}?maximumConnections=1000&wireFormat.maxFrameSize=104857600"
discoveryUri="multicast://225.5.5.5:6555?group=GROUP_WEB" />
</transportConnectors>
root-broker.xml:
<!-- Advertise root broker (service and web will connect to this) -->
<transportConnectors>
<transportConnector name="openwire"
uri="tcp://${broker.ip}:${broker.port}?maximumConnections=1000&wireFormat.maxFrameSize=104857600"
discoveryUri="multicast://225.5.5.5:6555?group=GROUP_BROKER" />
</transportConnectors>
Do the configurations shown above support the architecture shown above?
Do you see any other problems/pitfalls?