Run Alertmanager with -target=all (monolithic mode)

[pracucci]

Alertmanager is the only Mimir component (among the ones used in a standard setup) that isn't started in monolithic mode (-target=all.

Question: what if we start Alertmanager with -target=all?

[pracucci]

I'm currently working on the experimental read-write deployment mode (#2749) and want to start Alertmanager by default. Adding Alertmanager to monolithic mode too will make it consistent.

[jedd]

Actually, that's not quite true : )

/ # /bin/mimir -modules
alertmanager
all
compactor *
distributor *
flusher
ingester *
overrides-exporter
purger *
querier *
query-frontend *
query-scheduler
ruler *
store-gateway *

Modules marked with * are included in target All.

Would it be worth qualifying that for new adopters at: https://grafana.com/docs/mimir/latest/operators-guide/architecture/components/alertmanager/

[pracucci]

Yeah, I consider overrides-exporter a really optional one. About query-scheduler we currently can't include it in monolithic mode (we need to guarantee only 2 replicas of it running, not more than that). We'll do some work around it for the read-write deployment, so after that we may consider to add it to monolithic mode.

Following this reasoning, alertmanager is the only one left.

[wilfriedroset]

If users run a single monolithic mimir (meaning a single alertmanager) they will face the bug explained in #2910.
Starting from two instances, until the bug is fixed, they should be ok.