> Even a synthetic probe needs a few failures to trigger an alert.

It doesn't "need" that. That just how most people set it up because it’s an easy sane default that allows for network jitter without inexperienced engineers thinking about different conditions triggering different types of responses.

If you’re measuring internal APIs from an observablity solution that’s has nodes already inside you’re network enclave, then there is a strong argument for alerting early.

> You should not alert on cpu, ram, etc

That’s not true to say as an absolute statement. And a generalisation it heavily depends on the system your monitoring and how it behaves under pressure.

But in any case, I wasn’t suggesting CPU alerts were the end goal. I said:

> these types of metrics are generally bespoke to the type of application your monitoring.

Ie you’ll use metrics but those metrics will be highly specific.

The CPU examples were an illustration as to what a “metric” is (it might seem obvious but not everyone is an expert) but the point was HTTP response codes aren't the only types of metrics one should be capturing and watching.

▲

lokar 2 hours ago | parent [-]

Ah, yes, I misunderstood. And I have seen cases where a direct CPU alert makes sense, but 99 times out of 100 times I see it, it's nothing but trouble. Worse, I tend to see the cpu alert when there are no end to end synthetic alerts, 500 alerts, queue depth alerts, etc.

If your requests are fast and cheap, you can probe frequently relative to your goals, but often that's not really possible (think, long SQL queries, or scheduling a container/pod). There you need several datapoints, or possible fewer augmented with other signals.

▲

hnlmorg an hour ago | parent [-]

Yeah very true.

Talking about long SQL queries, I quite like throwing CPU alerts on database servers. They'll be a low priority alert (ie no out of hours "pagers") so just something that goes into a slack channel. But they're a good indicator of when developers have poorly optimized SQL, or the DB schema is poorly defined (eg missing indexes), or the DB server itself is poorly sized.

This wouldn't be something you'd expect to need in production and definitely not something you'd rely on as a notice of a production outage. But it is an example of one of those 1% occasions where a CPU alert does add value to the overall observability of the application.

But this also ties into your excellent point about how you'd use CPU and other data points to build a picture of what's happening in your application.

	▲	lokar an hour ago \| parent [-]
		Oh, I was thinking about it as the person running SQL as a service. People run queries that go on for days.... idle CPU is often wasted CPU