Reporting internals

Module report cache and expiry

Version 0.1.16 introduces cached status reporting. Using agent configuration keys fetch_every and expires_after it is now possible to control module execution timing separately from report submission timing.

Internally, Gullveig agents will preserve the last report in memory and report the health status portion of the report to the reporting server with every reporting interval as if the status would be actual.

To prevent modules from silently failing, expires_after is used to indicate the validity period of each stored report. If a report becomes stale, status of such a stale report will no longer be reported to the server and health checks will fail.

expires_after should be reasonably long to prevent reports expiring in the middle of the module execution cycle.

A good example of how to determine a good expiry time is - if the fetch_every is set to 60 seconds, and module spends 30 seconds gathering data, expires_after should be no less than (report_delay * tolerance) + (60 + 30) seconds, where tolerance is the number of reporting cycles you would like for the report cache to survive.