Adopt Guru Meditation report¶
This spec proposes adoption for Oslo Guru Meditation reports in Cinder. The new feature will enhance debugging capabilities of all official Cinder services, by providing an easy way to gather runtime data about current threads and configuration, among other things, to developers, operators, and tech support.
Currently Cinder does not have a way to gather runtime data from active service processes. The only information that is available to deployers, developers, and tech support to analyze is what was actually logged by the service in question. Additional data could be usefully used to debug and solve problems that occur during Cinder operation. Among other things, we could be interested in stack traces of all (both green and real) threads, pid/ppid info, package version, configuration as seen by the service, etc.
Oslo Guru reports provide an easy way to add support for gathering this kind of information to any service. Report generation is triggered by sending a special (USR1) signal to a service. Reports are generated on stderr, that can be piped into system log, if needed.
Guru reports are extensible, meaning that we will be able to add more information to those reports in case we see it needed.
Guru reports has been supported by Nova.
First, a new oslo-incubator module (reports.*) should be synchronized into cinder tree. Then, each service entry point should be extended to register reporting functionality before proceeding to its real main().
Data model impact¶
REST API impact¶
In theory, the change could expose service internals to someone who is able to send the needed signal to a service. That said, we can probably assume that the user is already authorized to achieve a lot more than just having an access to stack traces and configuration used. Also, if deployers are afraid of the information leak for some reason, they could also make sure their stderr output is channeled into safe place.
Because this report is triggered by user, there is no need to add config option to turn on/off this feature.
Other end user impact¶
The feature does not require any additional resources until it’s triggered by the user. Default report generation is not expected to take too long. Report extensions will need to be assessed on case by case basis. In any case, reports are not expected to be generated too often and are assumed to be debugging capability, not something to trigger once per minute just in case.
Other deployer impact¶
Deployers may be interested in making sure those reports are collected somewhere (e.g. stderr should be captured by syslog).
We could reimplement the wheel, but we hopefully won’t.
sync reports.* module from oslo-incubator
adopt it in all cinder services using a wrapper located under cinder/cmd/…
reports.* module is currently going thru graduation consideration. In case it’s graduated into oslo.reports library before cinder switches to it, we won’t actually need to sync any code from oslo-incubator but instead add a new external oslo dependency. If Cinder switches to the module before graduation is complete, then we’ll need to adopt oslo.reports later as part of usual oslo liaison effort.
Automated tests are needed to ensure the guru report is working correctly.
User documentation will need to be updated to introduce this changes.
Developer documentation should be updated to include information on how to add support for the reporting feature.
oslo-incubator module: http://git.openstack.org/cgit/openstack/oslo-incubator/tree/openstack/common/report
blog about nova guru reports: https://www.berrange.com/posts/2015/02/19/nova-and-its-use-of-olso-incubator-guru-meditation-reports/
oslo.reports repo: https://github.com/directxman12/oslo.reports