Make Ruler/Alertmanager easy for new users

[friedrichg]

Is your feature request related to a problem? Please describe.
Users have trouble using ruler and alertmanager, because it provides too many modes of operation.

Describe the solution you'd like
We should make clear in the docs how a new user should use ruler and alertmanager and what options not to use (deprecated)

[dv-sharma]

Hi @friedrichg ,
I found some doc references for alertmanager configuration:

• https://cortexmetrics.io/docs/guides/alertmanager-configuration/.
• https://cortexmetrics.io/docs/configuration/configuration-file/#alertmanager_storage_config
• https://github.com/cortexproject/cortex-tools?tab=readme-ov-file#alertmanager

Could you please elaborate on what operation modes are you talking about

[friedrichg]

this is what I mean

cortex/pkg/alertmanager/alertmanager.go

Lines 183 to 199 in adbf198

	// We currently have 3 operational modes:
	// 1) Alertmanager clustering with upstream Gossip
	// 2) Alertmanager sharding and ring-based replication
	// 3) Alertmanager no replication
	// These are covered in order.
	if cfg.Peer != nil {
	level.Debug(am.logger).Log("msg", "starting tenant alertmanager with gossip-based replication")
	am.state = cfg.Peer
	} else if cfg.ShardingEnabled {
	level.Debug(am.logger).Log("msg", "starting tenant alertmanager with ring-based replication")
	state := newReplicatedStates(cfg.UserID, cfg.ReplicationFactor, cfg.Replicator, cfg.Store, am.logger, am.registry)
	am.state = state
	am.persister = newStatePersister(cfg.PersisterConfig, cfg.UserID, state, cfg.Store, am.logger, am.registry)
	} else {
	level.Debug(am.logger).Log("msg", "starting tenant alertmanager without replication")
	am.state = &NilPeer{}
	}