Well I experienced now the following:
- http_access_xxxx.log: Contains log of any HTTP access (in my case only the carbon admin jsp)
- wso2carbon.log: Contains the real log output of the Application Server (most important one)
- wso2carbon-trace-messages.log: Always empty - don't know what it is for
- wso2-esb-error.log: Lists all WARNING and ERROR message from the wso2carbon.log again here - no INFO or DEBUG messages
- wso2-esb-service.log: Contains all logs that have been made with the "Log" Mediator in Synapse Proxies or Sequences
- wso2-esb-trace.log: Always empty - don't know what it is for
Well just add your monitoring on the wso2carbon.log file and you have everything essential.