The Developer Tutorials blog has posted a new tutorial covering how to scan ports and checking a remote service's status with PHP.

Having access to the current status of public servers can empower your applications to make decisions and respond to problems automatically. Acknowledging a service is offline can also save endless support emails. In this tutorial, I'll show you how to keep track of your server status by scanning ports on your server with PHP.

They show how to check a remote instance (a socket open with a timeout) and how to run through a list of ports, looping from one to one-thousand and running an fsockopen on each. They make a sample script to show these two combined - a simple page that loops through the common protocols (HTTP, FTP, SSH, etc) and checks to see if the remote machine is running something on that port.