3:11 p.m.
Hello Everybody,
With the metrics aggregation work well under way, we have encountered the first case where
timezones are important. The task queue [1] that John wrote to be used in the aggregation
process is time sensitive. The tasks ran according to a schedule that is predefined; the
time relationship also applies to failures, retries, and cancellation. Based on the
experience we had with RHQ, not using an UTC timezone can lead to errors and loss of data
(for more details visit [2])
I propose to set the default time zone for all the services to UTC. Only allow the concept
of a timezone in the UI. This will avoid any problems due to automatic transitions between
DST and non-DST times. For example, if the user wants to schedule something 2 weeks from
now, let the UI handle the user selection. But when the user action is sent to the
backend, it should be expressed in an timezone agnostic manner (eg. milliseconds since
Unix Epoch).
The PR [1] sets the default timezone for the JODA library to be UTC for the classloader
that contains the metrics service. With the recent discussions about creating a combined
Kettle EAR or using a single classloader, that means this setting will extend to all the
services in the same classloader that use JODA. And this is just the default, if a service
really needs to set another timezone for a date object, it can be done by just specifying
the timezone.
We tried to make the change more local in the metrics code, but the approach was error
prone. Anybody could make a mistake and instantiate a date object in the current server
timezone rather than UTC. This global approach drastically limits inadvertent mistakes.
Two questions for the group:
1) Does anybody see any issues with using the UTC timezone as default at the services
layer?
2) Should we expand this setting to the JVM (not just JODA)?
[1] Task queue PR - https://github.com/hawkular/hawkular-metrics/pull/205
[2] Old RHQ thread -
https://lists.fedorahosted.org/pipermail/rhq-devel/2014-November/003709.html
Thank you,
Stefan Negrea
Software Engineer