As part of the effort to run Maestro on the Minicloud, I decided to tweak the Maestro broker used by the test cluster. The broker component provides the infrastructure for the test nodes to exchange messages. It is used, for example, to synchronize the start and stop of the test execution and share success and failure notifications.
Given the resource restrictions I mentioned on the previous post, I decided to setup a dual purpose node, serving both as a Maestro client and as as Maestro broker. The virtual machine I setup for this purpose has only 1 vCPU and 512 Mb of RAM. At first sight is looks pretty small, but it should be sufficient for running both of the tasks allocated for it.
To accommodate for these resources, I decided to deploy Apache Artemis as the Maestro Broker. One the cool things about Artemis is that it can run with ridiculously small amount of memory. The low scale of the Maestro Broker means that I can go pretty aggressive with the resource limitations and, as such, I decided go with as little as 32Mb of heap.
The first step to achieve this, is to adjust the artemis command-line for the download package. In its default setting, the heap is set to vary between 512Mb to 1Gb, which would exceed the capacity of the virtual machine I configured. This script runs the code that creates the broker instance, therefore, it’s not necessary to waste too much time tweaking it. Simply adjusting it for creating the broker instance should be sufficient.
This setting is adjusted on ${install.directory}/bin/artemis. The line to be changes is the one with JAVA_ARGS. I have adjusted the heap to a fixed size of 256Mb.
|
1 2 3 |
# Set Defaults Properties JAVA_ARGS="-XX:+UseParallelGC -XX:+AggressiveOpts -Xms256M -Xmx256M" CLASSPATH="$ARTEMIS_HOME/lib/artemis-boot.jar" |
With that setting in place, the instance can be created. For example:
|
1 |
./artemis create --nio --allow-anonymous --http-host 0.0.0.0 --user admin --password "admin" --role amq /home/maestro/apache-artemis-instance |
To start tweaking the instance, the java heap memory for the instance can be adjusted. That is done on the ${instance.directory}/etc/artemis.profile. Once again, the line to be adjusted is the one with JAVA_ARGS:
|
1 |
JAVA_ARGS=" -XX:+PrintClassHistogram -XX:+UseG1GC -XX:+AggressiveOpts -Xms32M -Xmx32M -Dhawtio.realm=activemq -Dhawtio.offline="true" -Dhawtio.role=amq -Dhawtio.rolePrincipalClasses=org.apache.activemq.artemis.spi.core.security.jaas.RolePrincipal -Djolokia.policyLocation=${ARTEMIS_INSTANCE_ETC_URI}jolokia-access.xml" |
That alone should be sufficient for the very low scale of the Maestro Broker. However, given the very low memory settings, it is a good idea to disable a couple of extra things: the console and unused acceptors.
To disable the console we can modify the ${instance.directory}/etc/bootstrap.xml. The trick is to remove (or comment) the web element and all its contents. This is the content that should be removed:
|
1 2 3 4 5 |
<web bind="http://0.0.0.0:8161" path="web"> <app url="activemq-branding" war="activemq-branding.war"/> <app url="artemis-plugin" war="artemis-plugin.war"/> <app url="console" war="console.war"/> </web> |
Then, the last trick is to leave only the acceptors that are intended to be used in this broker instance. Since Maestro broker relies on MQTT, that’s the only one that can be left there. The acceptors configuration for Apache Artemis should look like this:
|
1 2 3 |
<acceptors> <acceptor name="mqtt">tcp://0.0.0.0:1884?tcpSendBufferSize=1048576;tcpReceiveBufferSize=1048576;protocols=MQTT;useEpoll=true</acceptor> </acceptors> |
After that, the broker can be started. If you are unsure about the configuration, you can check the command lines using ps or jcmd.
In addition to these changes, the Artemis documentation mentions a lot of other tunnables that can be adjusted. For such a slow scale broker as this, I did not find the reason to adjust anything else other than what is mentioned here.