cinder/doc/source/contributor/gmr.rst

Guru Meditation Reports

Cinder contains a mechanism whereby developers and system administrators can generate a report about the state of a running Cinder executable. This report is called a Guru Meditation Report (GMR for short).

Generating a GMR

A GMR can be generated by sending the USR2 signal to any Cinder process with support (see below). The GMR will then output to standard error for that particular process.

For example, suppose that cinder-api has process id 8675, and was run with 2>/var/log/cinder/cinder-api-err.log. Then, kill -USR2 8675 will trigger the Guru Meditation report to be printed to /var/log/cinder/cinder-api-err.log.

There is other way to trigger a generation of report, user should add a configuration in Cinder's conf file:

[oslo_reports]
file_event_handler=['The path to a file to watch for changes to trigger '
                    'the reports, instead of signals. Setting this option '
                    'disables the signal trigger for the reports.']
file_event_handler_interval=['How many seconds to wait between polls when '
                             'file_event_handler is set, default value '
                             'is 1']

a GMR can be generated by "touch"ing the file which was specified in file_event_handler. The GMR will then output to standard error for that particular process.

For example, suppose that cinder-api was run with 2>/var/log/cinder/cinder-api-err.log, and the file path is /tmp/guru_report. Then, touch /tmp/guru_report will trigger the Guru Meditation report to be printed to /var/log/cinder/cinder-api-err.log.

Structure of a GMR

The GMR is designed to be extensible; any particular executable may add its own sections. However, the base GMR consists of several sections:

Package

Shows information about the package to which this process belongs, including version information

Threads

Shows stack traces and thread ids for each of the threads within this process

Green Threads

Shows stack traces for each of the green threads within this process (green threads don't have thread ids)

Configuration

Lists all the configuration options currently accessible via the CONF object for the current process

Adding Support for GMRs to New Executables

Adding support for a GMR to a given executable is fairly easy.

First import the module (currently residing in oslo-incubator), as well as the Cinder version module:

from oslo_reports import guru_meditation_report as gmr
from cinder import version

Then, register any additional sections (optional):

TextGuruMeditation.register_section('Some Special Section',
                                    some_section_generator)

Finally (under main), before running the "main loop" of the executable (usually service.server(server) or something similar), register the GMR hook:

TextGuruMeditation.setup_autorun(version)

Extending the GMR

As mentioned above, additional sections can be added to the GMR for a particular executable. For more information, see the inline documentation about oslo.reports: oslo.reports