PingAlive breaks down into two areas...

• The Website (the bit you see).
  
  This is a DotNetNuke based site. For those who haven't heard off, or used DNN before; its a web site that includes the tools to edit and maintain itself built in. Commonly known as a content management system (CMS). I've added a skin and designed the banner / logo myself.
  
  The PingAlive pages where you view your sites details were written in Visual Basic .Net. They access an SQL Server database that holds all the details of each site and its reponse times.
  
  Apart from that, theres not much else to it, just deciding on page structure and also what to bung in there in terms of text etc.
   
• The Pinger (the bit you don't see).
  
  This is a very simple program. It ticks every second, and at the start of every two minutes it gets a list of the websites that need 'pinged'. It spreads this list out so it does so many every second. Then on each tick it accesses the sites for that second. This way it uses the minimum resources to actually perform the accesses.
  
  Each access is done on its own thread since most of the time is spent waiting on a response. Once it gets a response it saves the details in an SQL Server database. If an unforeseen error occurs it is logged to a text file and the application exits. The scheduler tries to kick off a new process every 5 minutes if one doesn't already exist.
  
  Also there is a little mailer program that monitors a single table within the database every minute. If it finds an entry in the table is uses the data within to format an email to send out, and marks the entry as handled. The pinger program adds entries where required to this table.
  
  To perform the 'pings' themselves the program basically makes a request similar to what a browser would make to the site. The only major difference is that i use a HEAD request method which only pulls down the header rather than the full page. This keeps my bandwidth down to around half a kilobyte per 'ping'.