how could you "justify" that the service of apache is available and running well?

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http://serverfault.com – This could sound like a very commercial question, but I really dont know how to justify this, the problem is that sometimes the page due the internet conection (I think) doesnt load, and the browsers returns an error message, monitoring the server, with alerts and all stuffs (incluiding nagios) seems like all services are responding, if I check the memory of the server still 200mb free(enough like to answer a simple web request), there is any other way to contactly check the timeline of a service?? Any idea? (HowTos)