Help: My 'What is my IP Address' Tool Incorrectly Displays Public IP Address

Hello AdsVolt community!

I'm a fairly new developer, just dipping my toes into building and launching simple web tools. I recently launched a basic 'What is my IP Address' tool, hoping it would be a straightforward way to learn more about server-side operations and user interaction.

However, I've hit a bit of a snag, and I'm hoping some of the more experienced folks here can shed some light on what I'm doing wrong. The core problem is that my tool inconsistently displays the correct public IP address. Sometimes it works perfectly, showing the user's actual external IP. But other times, it shows an internal IP (like a 192.168.x.x address) or an IP that is clearly not the user's true public IP, which is really confusing for my users and me.

Here's what I've tried so far:

• Attempted to retrieve the IP using standard server-side methods. For example, in Node.js, I've checked req.ip and also looked at various headers like X-Forwarded-For, CF-Connecting-IP, and True-Client-IP, hoping to find the real source.
• I've done some basic web server configurations (I'm using Nginx as a reverse proxy in front of my application server), trying to ensure it's correctly passing client IP information. But I'll admit, I'm quite new to advanced Nginx configurations.
• I've scoured numerous online tutorials and Stack Overflow posts, but many of them seem to offer similar solutions that haven't consistently resolved my issue.

My expectation is simple: the tool should always accurately detect and display the user's true public IP address, regardless of their network setup or whether they're behind a VPN (though I understand VPNs will show the VPN's IP, not their home IP).

Here's a dummy example of what I sometimes see in my logs or when testing, which doesn't reflect my actual public IP:

Client IP from req.ip: 172.17.0.1
X-Forwarded-For Header: 10.0.0.5, 192.168.1.1
CF-Connecting-IP Header: (not present)
True-Client-IP Header: (not present)
Detected Public IP by tool: 172.17.0.1 (Incorrect internal IP)

I'm really scratching my head here. Could someone please help me understand:

1. What are the most common reasons a 'What is my IP' tool might fail to show the correct public IP address, especially when a reverse proxy like Nginx is involved?
2. Are there specific proxy or load balancer configurations (e.g., Nginx, Cloudflare, etc.) I should be aware of or specific directives I must include to ensure the client's original IP is always forwarded correctly?
3. What is the most robust and reliable method or best practice to get a user's actual public IP in a production environment, taking into account various network setups and potential proxies?

Any guidance or pointers from the experts here would be incredibly helpful. I'm eager to learn and fix this! Thank you in advance for your time and wisdom.