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I want to make sure the site is UP and running. Is reading the HTTP GET Response enough?

What does services like PingDom test?

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3 Answers 3

up vote 1 down vote accepted

Usually monitoring of HTTP comes in one of three flavours:

  1. Checking whether a server is responding on a port - i.e a TCP connection is ACK'ed (check_tcp in nagios)
  2. Checking just the HTTP response code, i.e doing an OPTIONS or HEAD and ensuring that the HTTP response that comes back is either 2xx or 3xx (as opposed to 4xx or 5xx).
  3. Checking for a response like (2) - as well as checking for an expected string of text in the output.

Option 3 would be the most reliable, but requires a full GET of your page contents every time the monitoring server hits your server. Option 2 can be acheived with just a HTTP OPTIONS or HEAD, Option 1 can be done with just a connect().

PingDom probably would do option (3) I'd assume.

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Supposing I choose solution (3), what string should I expect? How do I know which one to expect? –  donald Jan 17 '11 at 18:30
    
This is usually pre-set by yourself. –  JamesHannah Jan 31 '11 at 14:02

Well, assuming you actually get a response, you can assume that the actual HTTP server is alive. If you wanted to test to see if the site was actually functional in addition to being online, you would have to read that response to ensure it's not an error page or something...

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If you also want to make sure site actually works (and is not just "up"), you should run some transaction monitoring or, better yet, real browser monitoring in addition to the standard http get and ping tests.

Of course, this is most important for complex websites that have many 3rd party services integrated, Ajax, Javascript etc. - It is not required for a simple static website.

See also http://en.wikipedia.org/wiki/Synthetic_monitoring

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