Automatic Update Of The jvmguard Agent

When you set up a JVM for monitoring, you copy the jvmguard agent files to the machine where the monitored JVM is running. When you update the jvmguard server, the question arises how the agent files are updated.

While the server is shut down during an update, so that all of its files can be replaced, the monitored JVM cannot be terminated just for updating a monitoring agent. This is why jvmguard performs an automatic deployment of agent updates whenever the server installation is updated.

Server Update

You can check for updates within the same major series in the global settings and update notifications are sent to you as inbox messages if automatic update checking is enabled.

When you update the jvmguard server, all monitoring agents are disconnected from the collector. However, the agents continue to record data and will transmit it to the collector when it becomes available again. After a disconnection, the agent will periodically try to reconnect to the jvmguard collector with diminishing frequency. Data is only discarded if its quantity exceeds limits that are considered unsafe with respect to memory overhead.

After a server update, the jvmguard agent may have changed with respect to the older version. In that case, the VMs view will show a  warning icon next to the VM name. The jvmguard server will continue to work with agents of all previous versions, but new functionality may not be available for JVMs that are being monitored with an outdated agent.

When the monitored JVM is restarted at some point in the future, the new agent will be used automatically. There is no need for you to transfer new agent files to remote machines.

Agent Update Mechanism

When connected to a JVM that is monitored with an outdated jvmguard agent, the jvmguard server transfers the new agent files to the remote machine. Because the original agent files are in use and may be write-protected, they cannot be overwritten. New agents are stored in the $HOME/.jvmguard/agent directory. In that directory there are subdirectories for each monitored VM that in turn contain directories with the transferred agents.

When a monitored JVM is started, it loads the jvmguard.jar Java agent that you have specified in the -javaagent JVM option. That Java agent bootstraps the actual implementation of the monitoring agent by looking into $HOME/.jvmguard/agent and selecting the most recent agent files for the monitored JVM. If no agents have been transferred, the implementation in the lib directory of the extracted agent archive is used.

While the jvmguard.jar file with the bootstrapping code is never updated, it performs a limited function at startup that does not impact the monitoring functionality itself. Even if the JAR file changes in a newer release, it does not mean that you have to replace it on any remote machines.