Probing regions, and what happens when one closes

What a region is

A probing region is a place we check from. When you pin a monitor to one, every check for it runs from machines there. Pin it to several and each one becomes an independent viewpoint, which is what lets us tell "your site is down" apart from "one route to your site is down".

The region code is an identifier for a viewpoint, not a claim about who runs the hardware behind it. We may replace the machines in a region without the code changing, and when we do, your monitors and your history carry on unbroken. If you allowlist our addresses on a firewall, that is the one case worth watching: the addresses can change even when the region does not. The current list is always at howlops.com/bot.

Regions can close

Occasionally a location stops being viable — a provider leaves a market, or we consolidate onto infrastructure that is better for everyone. When that happens your monitors need somewhere else to check from, and we would rather move them than let them quietly stop.

Here is exactly what we do, in order.

1. We tell you, with a date

Anyone with monitors on the region gets a notice naming the closing date and how many of their monitors are affected. Only the people actually using it: telling everybody would make the notice noise, and noise is how the one that mattered gets missed.

If you want to act on it yourself, that is the moment. Change the region on a monitor from its settings, or on several at once from the Monitors list. If you do nothing, read on.

2. We test the replacement against your actual monitors

Before we change anything, a prober in the replacement region checks the affected monitors once, and we compare the result against what the closing region currently reports.

Not all of them, and we would rather say so than round up. Only monitors that make an HTTP request can be tested this way: a ping, DNS or TCP monitor has no equivalent one-off check, so those are moved without a rehearsal. If a region has a great many monitors we test them in batches. Whichever monitors we could not test, we tell you that too, in the notification below.

This is not a formality, and it is the step we would most want you to know about. A site can be perfectly healthy from one country and blocked from another. Web application firewalls make decisions by geography, and CDNs answer from whichever location is nearest. Moving a monitor to a region that cannot reach your target would not break your site — it would do something more annoying, which is turn a working check into a false alarm at three in the morning.

These test checks do not appear in your monitor's history, do not affect its status, and never trigger an alert. They exist only to answer one question before we act on it.

3. Only then do we switch them over

If the replacement region reaches your targets, we move the affected monitors to it. Your history is kept, your alerting is unchanged, and the monitor keeps running on the same interval.

Any monitor the replacement region could not reach is left where it is. We would rather come back to you with a problem than hand you a monitor that fails for a reason that has nothing to do with your site. Those need sorting out individually, and we will be in touch about them.

4. We tell you we did it

Every workspace we touched gets a notification saying which region closed, how many monitors we switched, and where they went. If we were not able to test all of them first, the notification says that too, rather than implying we did. You can change the region on any of them straight afterwards, at any time, exactly as before.

Why we change your setting at all

Because the alternative is worse, though not in the way you might expect.

A monitor pinned to a region that no longer exists does not go quiet — we notice that none of its chosen regions has a prober and fall back to checking it from everywhere we have. So it keeps running. What it stops doing is the thing you asked for: it is no longer checked from the place you chose, and it is checked from a dozen places you did not. For a monitor whose whole point was "watch this from Singapore", that is a setting that has quietly stopped meaning anything.

Moving it to a real region restores the intent. A setting that points at nothing is not a preference worth preserving.

This is the only situation in which we change a monitor's region for you, it happens after an announced deadline, and we tell you both times.