You're looking for a guide on Eaglercraft 1.12.2, which seems to be a Minecraft mod or a custom version of Minecraft. Here's what I found:

Multiplayer & LAN: Supports joining "cracked" Minecraft servers and features a "Shared Worlds" (formerly LAN) mode that uses WebRTC for direct peer-to-peer connections.

• Build client; sync dist/ to S3 bucket configured for static website hosting.
• Configure CloudFront distribution with HTTPS and set origin to S3.
• On VPS: install Node.js, clone server repo, npm install, configure env vars (PORT, WS_PATH), run systemd service.
• Point DNS to CloudFront (client) and to VPS (ws subdomain). Use nginx on VPS to terminate TLS and proxy /ws to Node.

Resource packs, skins, and assets

• Clients typically load assets from configured CDNs or local servers. CORS headers must allow cross-origin fetching.
• Skins support: many forks allow custom skin uploads or use Mojang skin URLs. For privacy/offline setups, skins can be hosted locally.
• Example asset pipeline:
  • Suggested folders and files for an Eaglercraft 1.12.2 repo: