Alerting

To summarize: keep alerting simple, alert on symptoms, have good consoles toallow pinpointing causes, and avoid having pages where there is nothing to do.

Aim to have as few alerts as possible, by alerting on symptoms that areassociated with end-user pain rather than trying to catch every possible waythat pain could be caused. Alerts should link to relevant consolesand make it easy to figure out which component is at fault.

Allow for slack in alerting to accommodate small blips.

Typically alert on high latency and error rates as high up in the stack as possible.

For error rates, page on user-visible errors. If there are errors further downthe stack that will cause such a failure, there is no need to page on themseparately. However, if some failures are not user-visible, but are otherwisesevere enough to require human involvement (for example, you are losing a lot ofmoney), add pages to be sent on those.

You may need alerts for different types of request if they have differentcharacteristics, or problems in a low-traffic type of request would be drownedout by high-traffic requests.

For offline processing systems, the key metric is how long data takes to getthrough the system, so page if that gets high enough to cause user impact.

For batch jobs it makes sense to page if the batch job has not succeededrecently enough, and this will cause user-visible problems.

While not a problem causing immediate user impact, being close to capacityoften requires human intervention to avoid an outage in the near future.

It is important to have confidence that monitoring is working. Accordingly, havealerts to ensure that Prometheus servers, Alertmanagers, PushGateways, andother monitoring infrastructure are available and running correctly.

As always, if it is possible to alert on symptoms rather than causes, this helpsto reduce noise. For example, a blackbox test that alerts are getting fromPushGateway to Prometheus to Alertmanager to email is better than individualalerts on each.

Supplementing the whitebox monitoring of Prometheus with external blackboxmonitoring can catch problems that are otherwise invisible, and also serves asa fallback in case internal systems completely fail.