Breaking Down Alertmanager: Regression Breaking Sigv4

After upgrading from Grafana v10.4.1 to v12.4.3, a routine Save & Test now breaks - no alerts fire, despite the plugin working flawlessly in the same sigv4 configuration. The issue centers on a subtle shift: the plugin no longer respects allowed_auth_providers in the SigV4 middleware, a fix that silently snaps in the regression. This isn’t a bug in the alert logic - it’s a misalignment in how auth settings propagate. nnHere’s the core: Grafana’s new plugin API dropped direct auth config injection via SigV4MiddlewareWithAuthSettings, replacing it with a stricter, centralized auth layer. This change explains the failure but leaves many users blind to the shift. nnPsychologically, it taps into our trust in stability - especially in monitoring tools where silence feels like failure. The panic: ‘It worked before, why now?’ But the root is technical: the plugin expects a config it no longer sends. nnHidden truths:

• The auth provider wasn’t passed, not ignored - just dropped.
• This change affects only frontend plugins, not Grafana core.
• No IAM roles or EC2 auth issues; it’s a frontend plugin edge case. nnDon’t panic - reproduce on v10.4.1 or v12.4.3, or test direct plugin configs. If all else fails, check Grafana’s plugin middleware docs. The fix? Either patch the auth config or confirm you’re using a compatible plugin version with sigv4 intact. nnIf alerts stop working without warning, verify your alertmanager’s auth mode mirrors the plugin’s - auth failures breed silent outages, even in stable systems.