HTTP/2 & HTTP/3

Also Known As

TL;DR

Explanation

HTTP/2 (2015) addresses HTTP/1.1 bottlenecks with: multiplexing (multiple requests over one TCP connection, no head-of-line blocking at the HTTP layer), header compression (HPACK), server push, and binary framing. HTTP/3 (2022) replaces TCP with QUIC (UDP-based), eliminating TCP head-of-line blocking and improving performance on lossy connections. For PHP applications, HTTP/2 is enabled at the web server/proxy layer (Nginx, Caddy, Cloudflare) — no PHP code changes required. HTTP/2 makes domain sharding and CSS/JS concatenation anti-patterns obsolete.

Common Misconception

Why It Matters

Common Mistakes

• Still bundling all JS/CSS into single files for HTTP/2 — multiplexing makes many small files efficient.
• Not enabling HTTP/2 on the web server — most modern nginx/Apache versions support it with a config change.
• HTTP/2 without HTTPS — browsers only support HTTP/2 over TLS.
• Not using HTTP/2 server push for critical resources — eliminates a round trip for known dependencies.

Code Examples

# nginx — HTTP/1.1 only:
server {
    listen 443 ssl;
    # Missing: http2 directive
    # listen 443 ssl http2; — enables HTTP/2
}

# Enable HTTP/2 in nginx
server {
    listen 443 ssl http2;  # add 'http2' here
    ssl_certificate     /etc/ssl/certs/yourapp.crt;
    ssl_certificate_key /etc/ssl/private/yourapp.key;

    # HTTP/2 Server Push (push critical CSS/JS with HTML response)
    location = / {
        http2_push /css/app.css;
        http2_push /js/app.js;
        proxy_pass http://php-fpm;
    }
}

# PHP — Link header triggers server push
header('Link: </css/app.css>; rel=preload; as=style, </js/app.js>; rel=preload; as=script');

# Benefits of HTTP/2:
# - Multiplexing: multiple requests over one connection
# - Header compression (HPACK)
# - Server push
# - Binary protocol (faster to parse)

# Verify: curl -I --http2 https://yourapp.com | grep HTTP

References

• ↗ https://developer.mozilla.org/en-US/docs/Web/HTTP/Overview
• ↗ https://http3-explained.haxx.se/

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