Migration Guide: HTTP/1.1 to HTTP/2

Migrating from HTTP/1.1 to HTTP/2

Migrating to HTTP/2 is one of the easiest performance wins for most websites. The protocol is backward-compatible, universally supported, and requires minimal application changes.

Prerequisites

1. TLS is required: All browsers require HTTPS for HTTP/2. If you are still serving HTTP, set up TLS first.
2. TLS 1.2 or later: HTTP/2 requires TLS 1.2+ with ALPN support.
3. Modern server software: Nginx 1.9.5+, Apache 2.4.17+, Caddy (any version), Node.js 8.4+.

Server Configuration

Nginx:

server {
    listen 443 ssl http2;
    ssl_certificate /path/to/cert.pem;
    ssl_certificate_key /path/to/key.pem;
    ssl_protocols TLSv1.2 TLSv1.3;
}

Apache:

Protocols h2 h2c http/1.1

Caddy: HTTP/2 is enabled by default with automatic TLS.

Remove HTTP/1.1 Workarounds

After enabling HTTP/2, remove these optimizations that become counterproductive:

1. Domain sharding: Multiple subdomains to bypass connection limits. HTTP/2 uses one connection — sharding adds DNS lookups and prevents connection reuse.
2. Image sprites: Combining images into one file. Individual images are more efficient with multiplexing and have better caching.
3. CSS/JS concatenation: Merging all scripts into one file. Smaller files cache independently and load in parallel.
4. Inlining: Embedding CSS/JS in HTML. Separate files can be cached and shared across pages.

Testing

1. Open Chrome DevTools > Network tab
2. Right-click the column headers and enable "Protocol"
3. Load your page — look for "h2" in the protocol column
4. Verify that all resources load correctly

Common Pitfalls

• Forgetting ALPN: Without ALPN, the browser cannot negotiate HTTP/2 during the TLS handshake
• Proxy interference: If a reverse proxy does not support HTTP/2, it may downgrade connections
• Connection coalescing: HTTP/2 may reuse a connection for different hostnames sharing the same IP and certificate