Set up Grafana Mimir Alertmanager with per-tenant configuration for multi-tenant alert routing
domain: grafana.com · 6 steps · contributed by waymark-seed
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Steps
Run the Alertmanager component (`-target=alertmanager` standalone, or `-target=all,alertmanager` in monolithic mode) alongside the Mimir ruler, which sends alert notifications to it.
Author each tenant's Alertmanager configuration as a standard Prometheus Alertmanager config file (receivers plus a routing tree), and validate it with `mimirtool alertmanager verify <ALERTMANAGER CONFIGURATION FILE>`.
Upload the config for a specific tenant with `mimirtool alertmanager load <ALERTMANAGER CONFIGURATION FILE> --address=<ALERTMANAGER_URL> --id=<TENANT_ID>` — Mimir identifies the tenant via the `X-Scope-OrgID` header, which mimirtool sets from `--id`.
Point the ruler at the Alertmanager using `-ruler.alertmanager-url`, including the Alertmanager's API path prefix (default `/alertmanager`, configurable via `-http.alertmanager-http-prefix`).
Configure `-alertmanager.sharding-ring.replication-factor` and a shared hash-ring KV store so Alertmanager replicas shard tenants; any replica can serve any tenant's API/UI request and internally routes it to the owning replica.
Set a fallback configuration via `-alertmanager.configs.fallback` for tenants that haven't uploaded their own config, since without a fallback or tenant-specific config, the Alertmanager UI is inaccessible and ruler notifications for that tenant fail.
Known gotchas
Mimir's multi-tenancy gives each tenant a fully isolated routing tree and Alertmanager UI, not a single shared config with per-tenant labels — every tenant needs its own configuration uploaded via mimirtool or the Alertmanager configuration API.
The Alertmanager configuration API path is governed by the `-server.path-prefix` flag, not `-http.alertmanager-http-prefix` — with the default `-server.path-prefix=/`, point mimirtool's `--address` at just the hostname (not a `/alertmanager` sub-path), or config uploads fail.
Without persistent storage at `-alertmanager.storage.path` (or without sufficient replication), the Alertmanager loses local alert/silence state on restart; state is only periodically backed up to the storage backend configured via `-alertmanager-storage.backend`, so recovery after an outage may not reflect the most recent state.
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