This is the Cloudflare tech stack / backend infrastructure (I want to thank Cloudflare for being so open about their infrastructure and services. They are arguably one of my biggest inspirations.)
Proxy: Pingora [Rust] [Apache-2.0 license] https://github.com/cloudflare/pingora (Formerly, Cloudflare used NGINX)
REST APIs: Golang (mostly) (runs on kubernetes pods)
Databases: PostgreSQL (for REST API and Dashboard) ClickHouse for logs
Anti-DDoS: eBPF XDP
Web App Firewall (WAF): Rust (formerly nginx + lua) using Wirefilter as engine (https://github.com/cloudflare/wirefilter)
Compute: Workerd [C++] [Apache-2.0 license] https://github.com/cloudflare/workerd (Cloudflare Workers)
Documentation/Developers: Starlight [MIT license] https://github.com/withastro/starlight (https://developers.cloudflare.com/)
Cloudflare main site: JS: [Static Site Generator (Gatsby -> React)], CSS: Tailwind CSS (https://www.cloudflare.com/)
Dashboard: JS: React (graphics, NVD3, D3, Mapbox)
---will update this so it makes more sense and takes into acocunt all services and get a consistent format