Debugging check_http

Owned by Anastasios Thomaidis
Last updated: Oct 27, 2023 by Matthew Hierholzer
3 min read
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.

LAST TESTED ON CHECKMK 2.2.0P1

Table of Contents


check_http has many valuable configuration options. Please click here for some of the more common ones. 


Debugging

Proxy

In the following examples, you will see references to myproxyip and proxy_port. Please replace this information with your own proxy IP and port number.

Debugging with curl

If you have trouble using check_http, you can start to query the URL with curl:

curl -x myproxyip:proxy_port https://www.google.com/ --verbose

Execute the active Check manually

There are several ways to access the command. One way is described here: Configuring Check Email (check_mail)#ExecuteactiveCheckmanually

One other way is with cmk -N:

OMD[mysite]:~/lib/nagios/plugins$ cmk -N |grep http
  check_command                 check_mk_active-http!'-u' 'https://www.google.com/' '--ssl' '--onredirect=follow' '-j' 'CONNECT' '--sni' '-p' 'proxy_port' 'myproxyip' 'www.google.com'
  command_line                  /omd/sites/mysite/lib/nagios/plugins/check_http $ARG1$
  command_name                  check_mk_active-http

cmk -N will show you the nagios config. Active Checks in Checkmk are based on nagios.



A second way to access the command is via livestatus:

OMD[mysite]:~/lib/nagios/plugins$ lq "GET services\nColumns:host_name description check_command_expanded\nFilter: host_name = mysite\nFilter: description = myservicename"
localhost;HTTPS HTTPS;check_mk_active-http!'-u' 'https://www.google.com/' '--ssl' '--onredirect=follow' '-j' 'CONNECT' '--sni' '-p' 'proxy_port' 'myproxyip' 'www.google.com'

In both cases: Copy the parameters after the '!' for executing the command later.



Now you need to run the check_http and paste the copied parameters:

OMD[mysite]:~/lib/nagios/plugins$ ./check_http '-u' 'https://www.google.com/' '--ssl' '--onredirect=follow' '-j' 'CONNECT' '--sni' '-p' 'proxy_port' 'myproxyip' 'www.google.com'


For a detailed log, you can use --verbose at the end of the command:

OMD[mysite]:~/lib/nagios/plugins$ ./check_http '-u' 'https://www.google.com/' '--ssl' '--onredirect=follow' '-j' 'CONNECT' '--sni' '-p' 'proxy_port' 'myproxyip' 'www.google.com' --verbose


For more information, you can use --help command flag.

OMD[mysite]:~/lib/nagios/plugins$ ./check_http --help

Debugging Regular Expressions (Regex)

Javascript

If there is any client-side or Javascript-related content, Checkmk will not be able to parse this information with regular expressions.


In the following example, we are using regular expressions on status.cloud.google.com to gather Access Content Manager information. 

Example Check HTTP service


The service check returns OK

Screenshot of HTTP check OK


Running the command by hand can help debug issues as well.

OMD[mysite]:~/lib/nagios/plugins$ ./check_http -u /regional/americas --ssl -l -R 'Access Context Manager' --sni -I status.cloud.google.com -H status.cloud.google.com 
HTTP OK: HTTP/1.1 200 OK - 584329 bytes in 4.511 second response time |time=4.511160s;;;0.000000;10.000000 size=584329B;;;0;


Some important options

  • Address (name / IP or Proxy)  → If you need a proxy to access the domain
  • Virtual host → is necessary if you have multiple domains and one host running
  • How to handle redirect → How to handle redirected pages
  • Regular Expression to expect in content → Used to parse particular content from websites. 
  • HTTP Method → Set to CONNECT if you're using a proxy


    Example configuration of Check HTTP service.