The Java buildpack logs to both
<app dir>/.buildpack-diagnostics/buildpack.log and standard error.
Logs are filtered according to the configured log level.
If the buildpack fails with an exception, the exception message is logged with a
log level of ERROR whereas the exception stack trace is logged with a log
level of DEBUG to prevent users from seeing stack traces by default.
The LoggerFactory class in the JavaBuildpack::Diagnostics module
manages a single instance of a subclass of the standard Ruby Logger.
In normal usage, the Buildpack class creates a logger which is shared
by all other classes and which is retrieved from the LoggerFactory as necessary:
logger = LoggerFactory.get_logger
This logger is used like the standard Ruby logger and supports both parameter and block forms:
logger.info('success')
logger.debug { "#{costly_method}" }
The log level is configured by setting an environment variable
$JBP_LOG_LEVEL to one of:
DEBUG | INFO | WARN | ERROR | FATAL
For example:
cf set-env <app name> JBP_LOG_LEVEL DEBUG
If JBP_LOG_LEVEL is not set, the default log level is read from the configuration in
config/logging.yml.
The logging levels in JBP_LOG_LEVEL and config/logging.yml may be
specified using any mixture of upper and lower case.
Ruby's verbose and debug modes override the default log level to DEBUG unless
JBP_LOG_LEVEL has been set, in which case this takes priority.