Checks and regions

What one check does, where it runs from and how often. Read this when a result surprises you.

What each check does

The first three need no more than the address. Check page content and check a server, port or DNS record walk through the setup.

Website checks in detail

Method. up4 sends the method shown under HTTP method. The app preselects GET. A monitor created through the API without a method uses HEAD. A keyword check always uses GET, because a HEAD answer has no page to read. If a server answers a HEAD request with 405 Method Not Allowed, set the method to GET.

Redirects. up4 follows redirects to the final page by default and judges that answer. With Follow redirects off, the redirect itself is the answer, so a 301 counts as down unless you expect it as the status. Keep cookies when redirecting carries cookies along a redirect chain.

What counts as up. A 2xx status, unless you chose an exact status or a keyword. Any other status, a refused or reset connection, a failed name lookup and a timeout all count as down.

Body and headers. A request body goes out only with POST, PUT and PATCH, up to 8 KB. Basic auth and your own headers are sent with every check. The checker introduces itself as up4-checker/1.0; a user agent header you set wins.

What up4 reads. A keyword check reads the first 1 MiB of the page; the failure message says so when the word may sit beyond it. Other checks read only a small part of the answer. The checker does not run JavaScript, so a word that scripts add to the page after loading is not there for it.

Timeouts

The request timeout is how long up4 waits for an answer before the check counts as failed. It starts at 30 seconds and can go up to 1 minute per monitor. It applies to website, port and DNS checks. A ping never waits longer than a few seconds.

Certificates and domains

Over HTTPS, up4 checks the certificate by default. An expired, untrusted or mismatched certificate makes the check fail. Verify the TLS certificate can be switched off for a test server that uses a self-signed certificate.

Two optional warnings reach you before it happens: Certificate expiry warning counts days to the certificate's end, Domain expiry warning days to the end of the domain registration. Both are off until you set them.

Regions

A check runs from a region: Europe, North America, Asia or Australia. The picker offers only regions that have a checker online. If you pick one that has just gone quiet, up4 says that no checker is online there and asks you to try again in a minute. How many regions one monitor may use depends on your plan.

Checks come from fixed addresses and identify themselves. Where checks come from lists them, so you can allow them in a firewall.

Each region runs every check on its own, so regions multiply the cost: a monitor checked every minute from one region costs about €0.39 a month, from three regions about €1.17.

Several regions

With more than one region, up4 compares them before it alerts: a majority of the monitor's regions must agree, each judged by its latest result within 2 minutes. One region with a bad route to your site does not wake anyone. When you get alerted explains the full rule.

Intervals

The interval is the time between two checks. Your plan sets the shortest one; up4 refuses a shorter interval and names the minimum. Above that minimum, any whole number of seconds works through the API, and the app offers presets. The app's forms start at three minutes; a monitor created through the API without an interval gets 1 minute.

Monitors that use POST, PUT, PATCH or DELETE need an interval of at least 1 minute.

Shorter intervals notice an outage sooner and cost more, see what costs money. The time until an alert depends on more than the interval.

Slow servers

Response time is measured on every check. degraded is a separate, optional signal: with slowdown alerts on, 3 slow checks in a row mark the monitor as degraded, and 3 fast ones clear it. Without a threshold of your own, up4 learns the usual response time of the target.

A server that keeps answering far slower than the interval can also be checked less often than you set, so up4 does not hammer it. A server that is down keeps its set interval.