Setting up Fedora to use an external ActiveMQ instance.

Download the latest ActiveMQ 5 Linux .tar.gz from https://activemq.apache.org/components/classic/download
Unpack the file and move it under /opt (or where ever you like, just remember this directory)
Create a symlink from the unpacked directory to /opt/activemq (optional, makes it easier to handle updates later)
Create an activemq user:
sudo adduser --system --no-create-home activemq
Change ownership:
sudo chown -R activemq:activemq /opt/activemq/
Set up the unit file in /usr/lib/systemd/system/activemq.service
[Unit]
Description=Apache ActiveMQ
After=network-online.target

[Service]
Type=forking
WorkingDirectory=/opt/activemq/bin
ExecStart=/opt/activemq/bin/activemq start
ExecStop=/opt/activemq/bin/activemq stop
Restart=on-abort
User=activemq
Group=activemq
[Install]
WantedBy=multi-user.target
Choice! You can disable the connectors for the internal Fedora ActiveMQ instance and have it ONLY forward messages, or you can choose to have both ActiveMQ instances available.

Disable the internal ActiveMQ connectors

Edit your Fedora properties file (i.e. /opt/fedora/fcrepo.properties) and add some properties to customize the configuration and file location for the internal Fedora ActiveMQ:
```
fcrepo.activemq.configuration=file:///opt/fedora/config/activemq.xml
fcrepo.activemq.directory=/opt/fedora/queue
```

Create /opt/fedora/config/activemq.xml (this is the default Fedora ActiveMQ configuration with a fedora_bridge network connector to forward messages to your external ActiveMQ)

Note the networkConnector element, the username/password is needed if you have enabled authentication on the external ActiveMQ and the uri points to the external ActiveMQ hostname and OpenWire port

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
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://www.springframework.org/schema/context
   http://www.springframework.org/schema/context/spring-context-3.0.xsd
   http://activemq.apache.org/schema/core http://activemq.apache.org/schema/core/activemq-core.xsd">
<context:property-placeholder/>
    <bean id="activeMqDirectory" class="java.lang.String">
        <constructor-arg value="#{fedoraPropsConfig.activeMqDirectory}"/>
    </bean>
    <!--
        The <broker> element is used to configure the ActiveMQ broker.
    -->
    <broker xmlns="http://activemq.apache.org/schema/core" brokerName="localhost">
        <networkConnectors>
            <networkConnector name="fedora_bridge" username="fedora_user" password="<redacted>" dynamicOnly="true" uri="static:(tcp://localhost:61616)">
                <dynamicallyIncludedDestinations>
                    <topic physicalName="fedora"/>
                    <queue physicalName="fedora"/>
               </dynamicallyIncludedDestinations>
           </networkConnector>
        </networkConnectors>
    <!--
        For better performances use VM cursor and small memory limit.
        For more information, see:
            http://activemq.apache.org/message-cursors.html
        Also, if your producer is "hanging", it's probably due to producer flow control.
        For more information, see:
            http://activemq.apache.org/producer-flow-control.html
     -->
        <destinationPolicy>
            <policyMap>
                <policyEntries>
                    <policyEntry topic=">" producerFlowControl="true">
                    <!-- The constantPendingMessageLimitStrategy is used to prevent
                           slow topic consumers to block producers and affect other consumers
                           by limiting the number of messages that are retained

                           For more information, see:
                           http://activemq.apache.org/slow-consumer-handling.html
                     -->
                        <pendingMessageLimitStrategy>
                            <constantPendingMessageLimitStrategy limit="1000"/>
                        </pendingMessageLimitStrategy>
                   </policyEntry>
                   <policyEntry queue=">" producerFlowControl="true" memoryLimit="1mb">
                   <!-- Use VM cursor for better latency
                           For more information, see:
                           http://activemq.apache.org/message-cursors.html
                       <pendingQueuePolicy>
                           <vmQueueCursor/>
                       </pendingQueuePolicy>
                    -->
                  </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>
      <!--
         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="#activeMqDirectory"/>
      </persistenceAdapter>
      <!--
       The systemUsage controls the maximum amount of space the broker will
       use before slowing down producers. For more information, see:
       http://activemq.apache.org/producer-flow-control.html
       If using ActiveMQ embedded - the following limits could safely be used:
      -->
     <systemUsage>
          <systemUsage>
               <memoryUsage>
                    <memoryUsage limit="20 mb"/>
               </memoryUsage>
               <storeUsage>
                    <storeUsage limit="1 gb"/>
               </storeUsage>
               <tempUsage>
                    <tempUsage limit="100 mb"/>
               </tempUsage>
          </systemUsage>
      </systemUsage>

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

Keep both ActiveMQ instances available
1. Edit /opt/activemq/conf/activemq.xml and change port numbers in the transportConnectors section (to avoid conflicts with Fedora’s built-in ActiveMQ):
  1. 61616 -> 41616
  2. 61613 -> 41613
2. Start and enable the service:
  sudo systemctl enable activemq
  sudo systemctl start activemq
3. Edit your Fedora properties file (i.e. /opt/fedora/fcrepo.properties) and add some properties to customize the configuration and file location for the internal Fedora ActiveMQ: fcrepo.activemq.configuration=file:///opt/fedora/config/activemq.xml fcrepo.activemq.directory=/opt/fedora/queue
4. Create /opt/fedora/config/activemq.xml (this is the default Fedora ActiveMQ configuration with a fedora_bridge network connector added to forward messages to port 41616)
  <?xml version="1.0" encoding="UTF-8"?>
  <beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:context="http://www.springframework.org/schema/context"
  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://www.springframework.org/schema/context
     http://www.springframework.org/schema/context/spring-context-3.0.xsd
     http://activemq.apache.org/schema/core http://activemq.apache.org/schema/core/activemq-core.xsd">
  <context:property-placeholder/>
      <bean id="activeMqDirectory" class="java.lang.String">
          <constructor-arg value="#{fedoraPropsConfig.activeMqDirectory}"/>
      </bean>
      
      <broker xmlns="http://activemq.apache.org/schema/core" brokerName="localhost">
          <networkConnectors>
              <networkConnector name="fedora_bridge" dynamicOnly="true" uri="static:(tcp://localhost:41616)">
                  <dynamicallyIncludedDestinations>
                      <topic physicalName="fedora"/>
                      <queue physicalName="fedora"/>
                 </dynamicallyIncludedDestinations>
             </networkConnector>
          </networkConnectors>
      
          <destinationPolicy>
              <policyMap>
                  <policyEntries>
                      <policyEntry topic=">" producerFlowControl="true">
                      
                          <pendingMessageLimitStrategy>
                              <constantPendingMessageLimitStrategy limit="1000"/>
                          </pendingMessageLimitStrategy>
                     </policyEntry>
                     <policyEntry queue=">" producerFlowControl="true" memoryLimit="1mb">
                     
                    </policyEntry>
                </policyEntries>
            </policyMap>
        </destinationPolicy>
        
        <managementContext>
            <managementContext createConnector="false"/>
        </managementContext>
        
        <persistenceAdapter>
            <kahaDB directory="#activeMqDirectory"/>
        </persistenceAdapter>
        
       <systemUsage>
  <systemUsage>
                 <memoryUsage>
                      <memoryUsage limit="20 mb"/>
                 </memoryUsage>
                 <storeUsage>
                      <storeUsage limit="1 gb"/>
                 </storeUsage>
                 <tempUsage>
                      <tempUsage limit="100 mb"/>
                 </tempUsage>
            </systemUsage>
        </systemUsage>
        
        <transportConnectors>
         
             <transportConnector name="openwire"
                 uri="tcp://0.0.0.0:#{fedoraPropsConfig.jmsPort}?maximumConnections=1000&wireformat.maxFrameSize=104857600"/>
             <transportConnector name="stomp"
                 uri="stomp://0.0.0.0:#{fedoraPropsConfig.stompPort}"/>
        </transportConnectors>
        
        <shutdownHooks>
             <bean xmlns="http://www.springframework.org/schema/beans"
                 class="org.apache.activemq.hooks.SpringContextHook"/>
        </shutdownHooks>
  </broker>
     
  </beans>
5. Reconfigure Camel Toolbox by editing your camel toolbox properties (i.e. /opt/fedora/config/fcrepo-camel-toolbox.properties) and adding:
  jms.brokerUrl=tcp://localhost:41616
6. Restart Camel Toolbox

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Setting up Fedora to use an external ActiveMQ instance.