Build a Monitoring Extension Using Java

You can create Java monitoring extensions that enable the Machine Agent and Server Visibility to collect custom metrics, which you define and provide, and report them to the Controller. This is an alternative to adding monitoring extensions using scripts.

When you capture custom metrics with a monitoring extension, they are supported by the same AppDynamics services that you get for the standard metrics captured with the AppDynamics application and machine agents. These services include automatic baselining, anomaly detection, display in the Metric Browser, availability for display on custom dashboards and availability for use in policies to trigger alerts and other actions.

This topic describes how to create a monitoring extension in Java.

To the agent, a monitoring extension is a task that runs on a fixed schedule and collects metrics. 

Before You Begin

Before creating your own extension from scratch, review the extensions on the AppDynamics community. The extensions are described and their source is available for free download at:

https://github.com/Appdynamics/

New extensions are constantly being added. It is possible that someone has already created what you need or something close enough that you can download it and use it after making a few simple modifications.

Overview of Creating a Monitoring Extension

To create a monitoring extension in Java:

1. Create your extension class. See Create the Monitoring Extension. 
2. Create a monitor.xml configuration file. See Create the monitor.xml File.
3. Create a subdirectory (<your_extension_dir>) under <agent_home>/monitors.
4. Place the extension class file and the monitor.xml file (plus any dependent jar files) in <your_extension_dir>.

5. Enter the Controller access information and credentials. See Configure the Machine Agent.

   

   Make sure that your controller-info and command line parameters are correctly configured. Required properties include Controller name, port number, and account access key. 

6. Restart the Machine Agent.

Create the Monitoring Extension Class

Create a monitoring extension class by extending the AManagedMonitor class in the com.singularity.ee.agent.systemagent.api package. This package is included in the MachineAgent.jar file. 

Your monitor extension class performs these tasks:

• Populates a hash map with the values of the metrics that you want to add to AppDynamics.
  How you obtain these metrics is specific to your environment and to the source from which you derive your custom metrics.
• Defines the type of metrics to collect using the MetricWriter class. See Metric Processing Qualifier.
• Uploads the metrics to the Controller using the execute() method of the AManagedMonitor class.

Example source code is here: Extension_Class_Source.txt.

Metric Path

All custom metrics processed by the Machine Agent and Server Visibility appear in the Metric Browser > Application Infrastructure Performance. Use the "I" character to specify the path from Application Infrastructure Performance to the custom metric. If the metrics apply to a specific tier, use the metric path for the tier, with "Component" followed by a colon ":"  and the tier name or tier ID. 

For example, suppose you want to associate a metric with tier AccountService. In this case, you would specify the metric path as follows:

• Server|Component:AccountService|Custom Metrics|Path|

The metric would then appear under the following tree in the Metric Browser:

You can report a custom metric only to the tier that is associated with the Machine Agent. If you try to publish metrics to a different tier, the metrics will not be reported.

You can insert a custom metric alongside an existing type of metric. For example, the following declaration causes the custom metric named pool usage to appear alongside the JMX metrics:

• name="Server|Component:<tier-name>|JMX|Pool|First|pool usage",value=10

The metric can then be used in health rules as would other types of JMX metrics. 

You can test the appearance of your custom metric in the Controller API by posting the metric data to the Machine Agent's REST API. Pass the path, name type and values of the metric as URL arguments. See Machine Agent HTTP Listener for more information.

Metric Names

Metric names must be unique within the same metric path but need not be unique for the entire metric hierarchy.

Try to use short metric names so that they are visible when they are displayed in the Metric Browser.

Prepend the metric path to the metric name when you upload the metrics to the Controller.

Metric Processing Qualifier

The Controller has various qualifiers for how it processes a metric with regard to aggregation, time rollup and tier rollup.

There are three types of metric qualifiers:

• Aggregation qualifier
• Time roll-up qualifier
• Cluster roll-up qualifier

You specify these options with the enumerated types provided by the MetricWriter class. These types are defined below.

Aggregation Qualifier

The aggregator qualifier specifies how the Machine Agent aggregates the values reported during a one-minute period.

Specify the aggregation qualifier as aggregator="aggregator type"

This value is an enumerated type. Valid values are:

Time Roll Up

The time-rollup qualifier specifies how the Controller rolls up the values when it converts from one-minute granularity tables to 10-minute granularity and 60-minute granularity tables over time.

Cluster Roll Up

The cluster-rollup qualifier specifies how the controller aggregates metric values in a tier.

For example, if a tier has two nodes, Node A and Node B, and Node A has 3 errors per minute and Node B has 7 errors per minute, the INDIVIDUAL qualifier reports a value of 5 errors per minute and COLLECTIVE qualifier reports 10 errors per minute. INDIVIDUAL is appropriate for metrics such as % CPU Busy where you want the value for each node. COLLECTIVE is appropriate for metrics such as Number of Calls where you want a value for the entire tier.

Sample Monitoring Extension Class

The NGinXMonitor class gets the following metrics from the Nginx Web Server and adds them to the metrics reported by AppDynamics:

• Active Connections: number of active connections
• Accepts: number of accepted requests
• Handled: number of handled requests
• Requests: total number of requests
• Reading: number of reads
• Writing: number of writes
• Waiting: number of keep-alive connections

The source for the extension class is included as an attachment.

Create monitor.xml

Create a monitor.xml file with a <monitor> element to configure how the Machine Agent executes the extension.

1. Set the <name> to the name of your Java monitoring extension class.
2. Set the <type> to managed.
3. The <execution-style> can be continuous or periodic.
   • Continuous means to collect the metrics averaged over time; for example, average CPU usage per minute. In continuous execution, the Machine Agent invokes the extension once and the program runs continuously, returning data every 60 seconds.

   • Periodic means to invoke the monitor at a specified frequency. In periodic execution, the Machine Agent invokes the extension, runs it briefly, and returns the data on the schedule set by the <execution-frequency-in-seconds> element. 
     

     

     Do not set the <execution-frequency-in-seconds> higher than 300 seconds (five minutes). The extension must collect metrics at least once every five minutes.

      

4. If you chose periodic for the execution style, set the frequency of collection in <execution-timeout-in-secs> element. The default frequency is 60 seconds. If you chose continuous, this setting is ignored.
5. Set the <type> in the <monitor-run-task> child element to java.
6. Set the <execution-timeout-in-secs> to the number of seconds before the extension times out.
7. Specify any required task arguments in the <task-arguments> element. The default arguments that are specified here are the only arguments that the extension uses. They are not set anywhere else.
8. Set the <classpath> to the jar file that contains your extension's classes. Include any dependent jar files, separated by semicolons.
9. Set the <impl-class> to the full path of the class that the Machine Agent invokes.

Sample monitor.xml Files

This attached monitor.xml file configures the NGinXMonitor monitoring extension. This extension executes every 60 seconds.

This attached monitor.xml file configures the MysqlMonitor. This monitor executes every 60 seconds, has four required task arguments and one optional task argument and one dependent jar file.