Today I have been playing around with my Nagios install and making a real effort to get all services on the Windows servers monitored effectively. One of these servers I have been looking at is running WSUS and a couple of other web based services on different ports.

I started to read up on the help file of the check_http plug-in, which up until now I had assumed (wrongly!) would just check for a web response on port 80 for the host you ran the check against.

Here is the help file from the current plug-in:

check_http v1.4.16 (nagios-plugins 1.4.16)
Copyright (c) 1999 Ethan Galstad <nagios@nagios.org>
Copyright (c) 1999-2011 Nagios Plugin Development Team
        <nagiosplug-devel@lists.sourceforge.net>

This plugin tests the HTTP service on the specified host. It can test
normal (http) and secure (https) servers, follow redirects, search for
strings and regular expressions, check connection times, and report on
certificate expiration times.

Usage:
 check_http -H <vhost> | -I <IP-address> [-u <uri>] [-p <port>]
       [-w <warn time>] [-c <critical time>] [-t <timeout>] [-L] [-a auth]
       [-b proxy_auth] [-f <ok|warning|critcal|follow|sticky|stickyport>]
       [-e <expect>] [-s string] [-l] [-r <regex> | -R <case-insensitive regex>]
       [-P string] [-m <min_pg_size>:<max_pg_size>] [-4|-6] [-N] [-M <age>]
       [-A string] [-k string] [-S <version>] [–sni] [-C <warn_age>[,<crit_age>]]
       [-T <content-type>] [-j method]
NOTE: One or both of -H and -I must be specified

Options:
 -h, –help
    Print detailed help screen
 -V, –version
    Print version information
 -H, –hostname=ADDRESS
    Host name argument for servers using host headers (virtual host)
    Append a port to include it in the header (eg: example.com:5000)
 -I, –IP-address=ADDRESS
    IP address or name (use numeric address if possible to bypass DNS lookup).
 -p, –port=INTEGER
    Port number (default: 80)
 -4, –use-ipv4
    Use IPv4 connection
 -6, –use-ipv6
    Use IPv6 connection
 -S, –ssl=VERSION
    Connect via SSL. Port defaults to 443. VERSION is optional, and prevents
    auto-negotiation (1 = TLSv1, 2 = SSLv2, 3 = SSLv3).
 –sni
    Enable SSL/TLS hostname extension support (SNI)
 -C, –certificate=INTEGER
    Minimum number of days a certificate has to be valid. Port defaults to 443
    (when this option is used the URL is not checked.)

 -e, –expect=STRING
    Comma-delimited list of strings, at least one of them is expected in
    the first (status) line of the server response (default: HTTP/1.)
    If specified skips all other status line logic (ex: 3xx, 4xx, 5xx processing)
 -s, –string=STRING
    String to expect in the content
 -u, –url=PATH
    URL to GET or POST (default: /)
 -P, –post=STRING
    URL encoded http POST data
 -j, –method=STRING  (for example: HEAD, OPTIONS, TRACE, PUT, DELETE)
    Set HTTP method.
 -N, –no-body
    Don’t wait for document body: stop reading after headers.
    (Note that this still does an HTTP GET or POST, not a HEAD.)
 -M, –max-age=SECONDS
    Warn if document is more than SECONDS old. the number can also be of
    the form “10m” for minutes, “10h” for hours, or “10d” for days.
 -T, –content-type=STRING
    specify Content-Type header media type when POSTing

 -l, –linespan
    Allow regex to span newlines (must precede -r or -R)
 -r, –regex, –ereg=STRING
    Search page for regex STRING
 -R, –eregi=STRING
    Search page for case-insensitive regex STRING
 –invert-regex
    Return CRITICAL if found, OK if not

 -a, –authorization=AUTH_PAIR
    Username:password on sites with basic authentication
 -b, –proxy-authorization=AUTH_PAIR
    Username:password on proxy-servers with basic authentication
 -A, –useragent=STRING
    String to be sent in http header as “User Agent”
 -k, –header=STRING
    Any other tags to be sent in http header. Use multiple times for additional headers
 -L, –link
    Wrap output in HTML link (obsoleted by urlize)
 -f, –onredirect=<ok|warning|critical|follow|sticky|stickyport>
    How to handle redirected pages. sticky is like follow but stick to the
    specified IP address. stickyport also ensures port stays the same.
 -m, –pagesize=INTEGER<:INTEGER>
    Minimum page size required (bytes) : Maximum page size required (bytes)
 -w, –warning=DOUBLE
    Response time to result in warning status (seconds)
 -c, –critical=DOUBLE
    Response time to result in critical status (seconds)
 -t, –timeout=INTEGER
    Seconds before connection times out (default: 10)
 -v, –verbose
    Show details for command-line debugging (Nagios may truncate output)

Notes:
 This plugin will attempt to open an HTTP connection with the host.
 Successful connects return STATE_OK, refusals and timeouts return STATE_CRITICAL
 other errors return STATE_UNKNOWN.  Successful connects, but incorrect reponse
 messages from the host result in STATE_WARNING return values.  If you are
 checking a virtual server that uses ‘host headers’ you must supply the FQDN
 (fully qualified domain name) as the [host_name] argument.

 This plugin can also check whether an SSL enabled web server is able to
 serve content (optionally within a specified time) or whether the X509
 certificate is still valid for the specified number of days.

 Please note that this plugin does not check if the presented server
 certificate matches the hostname of the server, or if the certificate
 has a valid chain of trust to one of the locally installed CAs.

Examples:
 CHECK CONTENT: check_http -w 5 -c 10 –ssl -H www.verisign.com

 When the ‘www.verisign.com’ server returns its content within 5 seconds,
 a STATE_OK will be returned. When the server returns its content but exceeds
 the 5-second threshold, a STATE_WARNING will be returned. When an error occurs,
 a STATE_CRITICAL will be returned.

 CHECK CERTIFICATE: check_http -H www.verisign.com -C 14

 When the certificate of ‘www.verisign.com’ is valid for more than 14 days,
 a STATE_OK is returned. When the certificate is still valid, but for less than
 14 days, a STATE_WARNING is returned. A STATE_CRITICAL will be returned when
 the certificate is expired.
 CHECK CERTIFICATE: check_http -H www.verisign.com -C 30,14

 When the certificate of ‘www.verisign.com’ is valid for more than 30 days,
 a STATE_OK is returned. When the certificate is still valid, but for less than
 30 days, but more than 14 days, a STATE_WARNING is returned.
 A STATE_CRITICAL will be returned when certificate expires in less than 14 days

Send email to nagios-users@lists.sourceforge.net if you have questions
regarding use of this software. To submit patches or suggest improvements,
send email to nagiosplug-devel@lists.sourceforge.net

So I set up a couple of service definitions which I thought I would share:
define service{
use                     web-check-service
host_name               pluto
service_description     HTTP Service – Port 8530 – Non SSL WSUS
check_command           check_http!-p 8530
}
define service{
use                     web-check-service
host_name               pluto
service_description     HTTP Service – Port 8531 – SSL WSUS
check_command           check_http!-p 8531 –ssl
}

define service{
use                     web-check-service
host_name               pluto
service_description     SSL Certificate Validity – WSUS
check_command           check_http!-p 8531 –ssl -C 30,14
}

I particularly like the last one which will go into warning when my SSL Cert is 30 days from expiration and critical when it is 14 days from expiration! Now to set up the tests for different Virtual Hosts running on my web servers too!