check_http (bogus) setup

[Marc Powell]

On Apr 15, 2010, at 3:50 AM, Gerard Petersen wrote:

> Hi All,
> 
> I've been testing with the check_http service. I always was under the 
> assumption that the setup below would check www.example.com

Why did you make this assumption? It's not documented to work like this.

>     check_command                   check_http!www.example.com!/

> With this service definition (as often installed out of the box):
> 
> define command{
>     command_name    check_http
>     command_line   /usr/lib/nagios/plugins/check_http -H '$HOSTADDRESS$'
>     }

It's not been like this in a long time I believe. Perhaps you've installed from a distribution specific package and they've deviated from current nagios? If so, there's nothing that we can do about that. This is what the official package uses --

# 'check_http' command definition
define command{
        command_name    check_http
        command_line    $USER1$/check_http -I $HOSTADDRESS$ $ARG1$
        }

Note that your assumed configuration still wouldn't work here but the official documentation expects this definition. See 'Monitoring HTTP' at http://nagios.sourceforge.net/docs/3_0/monitoring-publicservices.html.

> Wrong! It would check for a webserver on myhost1. Since there's nothing 
> running at myhost1:80 i got a TCP error. Somewhat baffled I've been tailing 
> the access.log of www.example.com to see when I actually got a hit.


> The funny thing is this (with no additional parms) even returns ok, would 
> you have a webserver listening on myhost1:80
> 
> check_command                   check_http

This is because your command_line doesn't use any of the params you think you're passing it ($ARG1$, $ARG2$).

> So, you would be wise to turn the command syntax into this:
> 
> command_line    /usr/lib/nagios/plugins/check_http -H '$ARG1$' -u '$ARG2$'

Or follow the example documented use of the plugin. In general, you can't make assumptions about how a plugin works without looking at, and understanding, the defined command_line for that plugin. Every one is different.

> Then this will actually test www.example.com:
> 
>  check_command                   check_http!www.example.com!/
> 
> Is it me or is this check_http setup misleading? (ubuntu 9.10 in this case)

No, but that would depend on the documentation you're referencing to use the plugin. If the ubuntu documentation says that your format works with their packaged version of the check_http command definition, then that is misleading and they should correct that. Otherwise it looks like you made an incorrect assumption about how something worked without understanding it. If I buy a car from a dealer and they tell me it runs on diesel, fill it up with diesel and it doesn't, then that's their fault. If they don't tell me anything about it and I assume it does without reading the manual, that's my fault.

For a new admin, the simplest use case is just to check that a web server is listening on a host. That's what your definition does and what the official definition does if no additional parameters are passed. As an admin becomes more familiar with the plugin and more sophisticated in what they want to do they need to edit either one or both of the command_line and check_command in your case but only the check_command in the official case. I think the official way provides the most flexibility all around, IMHO.

--
Marc


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