Icinga2 check_http fails to open socket

When you are executing the command manually, you are calling /usr/lib/nagios/plugins/check_http correct?

When you are calling check_http from the nagios config, it looks at /etc/nagios-plugins/config/http.cfg to determine the check_http command arguments.

What you need to do is create a custom check like:

define command {
    command_name                   check_web_content
    command_line                   $USER1$/check_http -H $HOSTADDRESS$ -t 60 -w 15 -c 45 -u $ARG1$ -s $ARG2$

}

Then in your service configuration your check_command should be something like:

check_command check_web_content!http://www.domain.com/index.html!"Text on site"

how do you define service in nagios?

it should be sth like this:

define command{
command_name    my_check_http
command_line    $USER1$/check_http -H$ARG1$ -I $HOSTADDRESS$
}

define host{
use                     generic-host
host_name               something
alias                   something
address                 192.168.1.52
# ...
}

define service{
use  generic-service
host_name something
check_http_args!nameofvhost
# ...
}