routinator_serial_info metric is sparse

[ties]

As a publication point operator I want to alert when my repository is not updating. For this I use an alert on the routinator_serial_info metric.

When doing so we sometimes hit a weird interaction between prometheus and this sparse metric, that we have worked around for now with a recording rule.

In practice this metric is sparse (it is empty when notification.xml is not modified). This causes increase alerts to fire (see the attached screenshots).

Expected behaviour: I expect routinator_serial_info to retain the old value when the notification file is not modified.

As discussed in DM with Martin: low priority/low impact, but nice to have.

[partim]

It’s a low priority/low impact kind of day today, so I just went ahead and fixed it …