Testing HTTPS Website which has multiple IPs with terminal

I. Problem

• A Domain can link to multiple IP.
• Web server is behind nginx as a reverse proxy, cannot call curl or wget directly to IP.
• Due to ISP blacklist, even though DNS does return IP list ex: nslookup example.com 1.1.1.1 (query IP for domain name example.com using dns server 1.1.1.1), however, web browser cannot access it.
• Don’t want to fetch http body, just header ONLY.

II. Solution

Create a file named test-https-ip.zsh (I use z-shell zsh). After creating this file, please do chmod +x and source it before use.

#!/bin/zsh
#set -x # Dev only

function test_https_ip() {
    domain_name="$1"
    ip_list_parsing=$(nslookup $domain_name | awk '/^Address: / {print $2}')
    ip_list=(${(f)ip_list_parsing})

    echo "Found IP: $ip_list"
    for ip in $ip_list; do
        curl -H "Host: $domain_name" --resolve $domain_name:443:$ip https://$domain_name  --head --max-time 3 &> /dev/null
        if [ $? -eq 0 ]; then
            echo "Status IP: $ip (OK)"
        else
            echo "Status IP: $ip (ERROR)"
        fi
    done
}

Explaination:

• set -x: for debug, displaying executing command while running
• awk: do parsing, extract IP from nslookup command
• ${(f)ip_list_parsing}: convert from nextline string to array list
• --max-time 3: total amount of time for a request is 3 seconds (avoid hanging).
• &> /dev/null: All info/error output from curl will go to /dev/null. Help beautifying TUI.

How to use it:

$ test_https_ip example.com