Stephen Finucane 83e7763518 doc: Populate the 'reference' section

Per the spec [1]:

  reference/ – any reference information associated with a project that
  is not covered by one of the above categories. Library projects should
  place their automatically generated class documentation here.

There are a couple of documents that focus on nova internals, but won't
necessarily be applicable to user. These are moved here.

[1] specs.openstack.org/openstack/docs-specs/specs/pike/os-manuals-migration

Change-Id: I94614c2383329e1fbed60d9c5aca3fab5170ef8f

2017-07-18 15:41:20 +01:00

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Guru Meditation Reports

Nova contains a mechanism whereby developers and system administrators can generate a report about the state of a running Nova 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 Nova process with support (see below). The GMR will then be outputted standard error for that particular process.

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

from oslo_reports import guru_meditation_report as gmr
from nova 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 under oslo.reports

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