What extension Health Checks are useful for debugging?

[#1]

What extension Health Checks generate logs I can use for debugging issues?

The Java SDK for AppDynamics Extensions runs a few checks to validate the Application and Machine Agent configuration and to ensure an error-free run of any configured extensions. These checks on validation (or failure) log messages in the Machine Agent logs to help debug any issues. These checks are primarily categorized into:

1. RunOnce Check: Runs only once on the start of the extension.
2. RunAlways Check: Run periodically based on the defined frequency.
   
   

RunOnce Check

1. AppTierNode Check: Ensures correct Machine Agent and SIM configuration with the following checks:
   1. ControllerInfo: Controller information can be configured either using System properties or via the controller-info.xml file present in the path <MachineAgent>/conf. Extension checks verify data from both places. In case the Controller information is not found in either of the places, then the missing ControllerInfo error message is logged.
   2. SIM Enabled: From the controller-info obtained in the previous step, this checks if SIM is enabled or not.
   3. Application/Tier/Node: Based on the result obtained in the previous step:
      1. When SIM is disabled, configuring the App/Tier/Node is mandatory, or an error will be reported.
      2. When SIM is enabled, App/Tier/Node does not need to be configured.
         
         
2. ExtensionPathConfig Check: Performs the following checks on the extension path configuration:
   1. Metric Prefix: Logs errors if the metric prefix retrieved from config.yml is null or empty.
   2. Tier ID: This check is performed as follows:
      • When SIM is enabled, there is no check for Tier ID.
      • When SIM is disabled, the Tier ID set in config.yml is verified with the TierName (or the corresponding Tier ID)  in controller-info.xml.
        
        
3. Machine Agent Availability Check: When SIM is disabled, this checks whether the Machine Agent Availability metric reports 1 or not. A GET request to the Controller for the following URL checks the MA availability:
   

   /controller/rest/applications/ApplicationName/metric-data?metric-
   path=ApplicationInfrastructurePerformance|TierName|Agent|Machine|Availability&time-range-
   type=BEFORE_NOW&duration-in-mins=15&output=JSON

RunAlways Check 

1. MaxMetricLimit Check: Machine Agent metrics limit is a frequently encountered error. Whenever this error occurs, the following message appears in the Machine Agent logs:
   

   ERROR   ManagedMonitorDelegate - Maximum metrics limit reached [450] no new metrics can be 
   created. This exception will not repeat until restart.

   The MaxMetricLimit check logs an error on any occurrences of this string in the Machine Agent logs. 
   
   
2. MetricBlacklistLimit Check: A Blacklist limit error is logged as in the following warning: 
   

   WARN ManagedMonitorDelegate - Metric registration blacklist limit reached

   This check looks up the Machine Agent logs for any occurrences of this string and, if found, logs the message and the error details.