// HAPI JS example
const Hapi = require('@hapi/hapi');
const getRequestIp = require('ip-from-request');

const init = async () => {
    const server = Hapi.server({ ... });

    server.route({
        method: 'GET',
        path: '/',
        handler: (request, h) => {
            const clientIp = getRequestIp(req); // e.g. 127.0.0.1
            // ...
        }
    });
    await server.start();
};

init();

The logic

The user ip is determined by the following order:

X-Client-IP
X-Forwarded-For (Header may return multiple IP addresses in the format: "client IP, proxy 1 IP, proxy 2 IP", so we take the the first one.)
CF-Connecting-IP (Cloudflare)
Fastly-Client-Ip (Fastly CDN and Firebase hosting header when forwared to a cloud function)
True-Client-Ip (Akamai and Cloudflare)
X-Real-IP (Nginx proxy/FastCGI)
X-Cluster-Client-IP (Rackspace LB, Riverbed Stingray)
X-Forwarded, Forwarded-For and Forwarded (Variations of #2)
req.connection.remoteAddress
req.socket.remoteAddress
req.connection.socket.remoteAddress
req.info.remoteAddress