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How to Enable HTTP/2 (and HTTP/3): Nginx, Apache, CDN

2025-08-13•9 min read

Want faster loads? Turn on HTTP/2 and, if possible, HTTP/3. This guide shows how to enable both on Nginx, Apache, and common CDNs, how to check they work, and quick fixes if they don't.

Why HTTP/2 (and HTTP/3)?

HTTP/1.1 opens multiple connections and repeats headers. HTTP/2 multiplexes requests over one connection and compresses headers. HTTP/3 adds QUIC over UDP to avoid transport-level blocking. Result: faster loads, especially on mobile and high-latency links.

Quick checks: are they on?

  • DevTools: Network tab > add "Protocol" column. Look for h2 or h3.
  • CLI: curl -I --http2 https://example.com
  • HTTP/3: curl -I --http3 https://example.com (recent curl)
  • Waterfalls: Many files should start together on one connection.

Nginx: enable HTTP/2 (and HTTP/3)

server {
   # HTTP/2
   listen 443 ssl http2;
   listen [::]:443 ssl http2;

   # Uncomment if your build supports QUIC
   # listen 443 quic reuseport;
   # add_header Alt-Svc 'h3=":443"; ma=86400' always;

   server_name example.com;

   ssl_protocols TLSv1.2 TLSv1.3;
   ssl_prefer_server_ciphers off;
   ssl_session_cache shared:SSL:10m;
   ssl_session_timeout 1d;

   add_header Strict-Transport-Security "max-age=31536000" always;
   # your SSL cert config here
}

Requirements: HTTP/2 module compiled in, TLS library with ALPN support. Most modern packages include both.

Apache: enable HTTP/2

# Load the module
LoadModule http2_module modules/mod_http2.so

# Enable globally or in a vhost
Protocols h2 http/1.1

# Optional: restrict to modern TLS
H2ModernTLSOnly on

Apache HTTP/3 support is experimental. Stick with HTTP/2 for production.

CDN: enable HTTP/2/3 (Cloudflare, CloudFront, Akamai, Fastly)

Most CDNs support HTTP/2 and HTTP/3. Turn them on for HTTPS traffic. Open UDP/443 if you run your own edge and want HTTP/3. If UDP is blocked, clients fall back to HTTP/2. The CDN to origin protocol is separate; use it if easy, but user impact comes from the edge.

Cloudflare

Dashboard > Speed > Optimization > HTTP/2 and HTTP/3 (enabled by default)

AWS CloudFront

Distribution settings > Supported HTTP Versions > HTTP/2 and HTTP/3

Fastly

Service configuration > Settings > HTTP/2 and HTTP/3 support

Verify + fallback behavior

Browsers negotiate automatically during TLS handshake using ALPN. If HTTP/3 fails (UDP blocked), they fall back to HTTP/2. If HTTP/2 fails (old server), they use HTTP/1.1. No manual intervention needed.

Check your setup:

  • Modern browsers show h2/h3 in DevTools Protocol column
  • Waterfall charts show parallel downloads on one connection
  • H3 often helps mobile/lossy links more than desktop

Troubleshooting

HTTP/2 not working?

  • Check if your server build includes the HTTP/2 module
  • Verify TLS library supports ALPN (OpenSSL 1.0.2+)
  • Ensure you're testing over HTTPS (browsers require it)
  • Check if a proxy/load balancer is downgrading to HTTP/1.1

HTTP/3 not working?

  • Verify UDP port 443 is open
  • Check if your build supports QUIC
  • Confirm Alt-Svc header is being sent
  • Test from different networks (some block UDP)

FAQs

Do I need HTTPS for HTTP/2?

Yes. Browsers only use HTTP/2 over TLS.

Is HTTP/3 required?

No, but enable it when you can. Keep HTTP/2 as fallback.

How do I check if HTTP/2/3 is active?

Use DevTools' Protocol column, or run curl with --http2 or --http3.

Why didn't enabling HTTP/2 change much?

App slowness and network loss still apply. Cache and profile your app; use HTTP/3 for lossy links.

Categories:

NginxPerformance