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Definition

Explain how to perform debugging when something doesn't work in Cargo

 

Sometimes, it can happen that the container does not start or stop as expected or you might have reasons to believe that CARGO is "acting weird". Here is a short list of things you can do to try debugging the problem.

Debugging the container

Most Java Virtual Machine implementations support remote debugging. Once started in debug mode, you can then remotely connect to your container using any IDE and debug your container and/or application.

In order to do so, add the following arguments to the JVM arguments configuration:

where:

  • suspend is whether the launch of the container should first wait for a remote debugger to connect. If y, the container will wait for you to connect with your remote debugger before starting; if n the container will start immediately and at the same time listen on the remote debugging port.
  • port is the port number to use for remote debugging.

Here is an example for starting a JOnAS 5.x container in Remote Debug on port 8000 without suspend mode using the Maven2 plugin:

Make sure the Debug arguments are only on one goal

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Please remember to map the Debug arguments to only one goal; else you will get exceptions such as the below when you try to stop your container:


[INFO] [talledLocalContainer] FATAL ERROR in native method: JDWP No transports initialized, jvmtiError=AGENT_ERROR_TRANSPORT_INIT(197)
[WARNING] [talledLocalContainer] ERROR: transport error 202: bind failed: Address already in use
[WARNING] [talledLocalContainer] ERROR: JDWP Transport dt_socket failed to initialize, TRANSPORT_INIT(510)
[WARNING] [talledLocalContainer] JDWP exit error AGENT_ERROR_TRANSPORT_INIT(197): No transports initialized [../../../src/share/back/debugInit.c:741]

 

Once the server is started, follow these steps to remotely debug your server and/or application:

  1. Click Debug - Attach Debugger...
  2. In the window that appears, type in the remote host name and the port number then click OK

Steps for achieving the same in Eclipse IDE are similar.

Redirecting container output to a file

Example using the Java API

The Container.setOutput(File) API allows you to redirect the container console (stdout) to a file. This is the first file you should check in case of problem.

Cargo is able to configure containers to generate various levels logs. There are 3 levels defined in o.c.c.container.property.LoggingLevel: LoggingLevel.LOW, LoggingLevel.MEDIUM and LoggingLevel.HIGH (LoggingLevel.MEDIUM is the default value). They represent the quantity of information you wish to have in the generated log file. You can tune container logging by using the following API:

The generated log files will then be found in the working directory you have specified on the container (through the container.setWorkingDir() call).

Starting Tomcat 4.x specifying an output console log file:

Use the container.setAppend(true|false) method to decide whether the log file is recreated or whether it is appended to, keeping the previous execution logs (by default, the file is recreated at every container start or stop).

Example using the Ant API

Starting Tomcat 4.x specifying an output console log file with the highest possible level of logs:

Use the append="true|false" attribute for controlling the log file creation behavior.

Example using the Maven2/Maven3 plugin

Starting Tomcat 4.x specifying an output console log file with the highest possible level of logs:

Use the append="true|false" attribute for controlling the log file creation behavior.

Debugging CARGO itself

To enable the Java debugger on ANT, export the ANT_OPTS system property using the parameters specified above. For example:

On Maven2/Maven3, enabling Java debugger is done using the mvnDebug executable instead of mvn.

mvnDebug command on MacOS X

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 Note that on MacOS X, mvnDebug is not on the default path. To run it, execute the command: /usr/share/maven/bin/mvnDebug

Redirecting CARGO logs to a file

Example using the Java API

Some Cargo classes support generation of logs. This is implemented through the notion of Logger and levels are managed using LogLevel. There are 3 levels defined in o.c.c.util.log.LogLevel: LogLevel.DEBUG, LogLevel.INFO and LogLevel.WARN (LogLevel.INFO is the default value).

For example to turn on logging monitoring on a Container class, you can use:

There are several Loggers that are readily available in the Cargo distribution:

Example using the Ant API

When using the Ant tasks, CARGO will by default use the AntLogger. You can specify the log level using the logLevel attribute, and the log file by using the log attribute. For example:

Example using the Maven2/Maven3 plugin

When using the Maven2/Maven3 plugin, CARGO will by default use the MavenLogger.

When you use mvn with the -e option, both Maven itself and the CARGO plugin will log everything in debug mode.

If you want to use the plugin in debug mode without having Maven itself in debug mode, you can specify the log level using the logLevel attribute, and the log file by using the log attribute. For example:

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