Ruler Notifier and Alertmanager use different API versions

[jtlisi]

The alertmanager and ruler notifiers are currently using two separate API versions.

Between

cortex/pkg/alertmanager/alertmanager.go

Line 134 in f69327c

am.api.Register(am.router.WithPrefix(path.Join(am.cfg.ExternalURL.Path, "/api/v1")))

and

cortex/pkg/ruler/notifier.go

Line 120 in f69327c

APIVersion: config.AlertmanagerAPIVersionV2,

We need to align these two configs if the ruler/alertmanager are going to work correctly. I'm not sure if this is related to #1592, the alertmanager will still work with the ruler, if the ruler is running a pre #1510 image.

#1597 Will fix this issue if the change I requested is added.

[bboreham]

Yes, this is the cause of the "no alerts" part of #1592 .

However just changing the API from v1 to v2 is likely to cause disruption as people upgrade. It's difficult to synchronise the upgrades of ruler and alertmanager.

[jtlisi]

I think the ruler should have the option to send to either. We can put V2 behind a flag