MAU prometheus metrics are broken

[turt2live]

Description

uh, t2bot.io's MAU count was reset with a synapse upgrade
it went from 1.20.0 to 1.21.2, and now there's only 38 active users apparently.
this is a big difference from the ~1 million it was before
hmm... the stats are still in the database - did the metrics change?
I've been using synapse_admin_mau:current{job="synapse",instance="t2bot.io"} as the query, which seems to be permanently stuck at 38?

Steps to reproduce

Unclear.

Version information

• Homeserver: t2bot.io

If not matrix.org:

• Version: now 1.21.2, up from 1.20.0 (with unrelated patches)
• Install method: pip
• Platform: differs

[turt2live]

because t2bot.io doesn't use MAU limiting, these are the settings as defined in homeserver.yaml:

track_appservice_user_ips: true
mau_stats_only: true

[richvdh]

apparently this was a deliberate change due to #8404. It's... regrettable... that that didn't get called out in the changelog.

[turt2live]

This is intentional from the looks of it. #8404 changed how the metric works, breaking the new metrics that t2bot.io is looking for into synapse_admin_mau_current_mau_by_service.

Seems the :current metric used in the issue description is for non-appservice users now.