TCP Monitors
A Port Monitor checks that a port on a host takes connections: a database, a mail server, a game server, or anything else that listens on a port. Choose Port when you press New Monitor.
Host and port
Section titled “Host and port”Host is a domain name, such as db.acme.com, or an IP address, without https:// and without a port. Port is the port to check. You cannot change either after you create the Monitor.
You can watch any port from 1 to 65,535. None is refused, not even a mail server’s: we send nothing, so there is nothing for the service on the port to misread. A Website Monitor refuses some ports for that reason, because it sends a request you write.
A host that is a private address, or a name that points to one, fails: we cannot reach it from the internet. Use a public address for the Monitor.
What counts as up
Section titled “What counts as up”On each run we open a connection to the port. When the host accepts it within the timeout, the run passes, and we close the connection at once. We send nothing, so no request of ours ever reaches the service on the port.
A run fails when the name cannot be found, when the host refuses the connection or resets it, when the host cannot be reached, or when nothing answers within the timeout.
The answer time of a run is how long the connection took to open, counted from looking up the name.
Timeout
Section titled “Timeout”How long a run may take, from looking up the name to the open connection: from 1 second to 30 seconds, and 10 seconds unless you change it.
Its Checks
Section titled “Its Checks”A Port Monitor carries the Uptime and the Performance Check. It reads no certificate. For a port that serves a website or an API over https, a Website Monitor checks the answer and the certificate as well.