While Windows Server 2012 R2 ships with IIS 8.5 by default, HTTP/2 support was officially introduced in IIS 10 (Windows Server 2016). Here's what you need to know about making HTTP/2 work in your environment:

Technically, you cannot directly upgrade IIS 8.5 to IIS 10 on Server 2012 R2. The only official Microsoft-supported path would require:

1. In-place upgrade to Windows Server 2016/2019
2. Clean installation of newer Windows Server version
3. Migration of IIS configuration using:
   - Web Deploy (msdeploy)
   - AppCmd export/import
   - Manual configuration backup

For environments where OS upgrade isn't feasible, consider these alternatives:

# Nginx reverse proxy configuration snippet
server {
    listen 443 ssl http2;
    server_name yourdomain.com;
    
    ssl_certificate /path/to/cert.pem;
    ssl_certificate_key /path/to/key.pem;

    location / {
        proxy_pass https://your-iis-server;
        proxy_set_header Host $host;
    }
}

Whether you choose to upgrade or use a workaround, ensure:

• TLS 1.2+ is enabled (HTTP/2 requires ALPN extension)
• Modern cipher suites are configured
• All certificates are valid and properly chained

After implementation, verify HTTP/2 is active:

# Using Chrome DevTools
1. Open Developer Tools (F12)
2. Navigate to Network tab
3. Look for "h2" in Protocol column

# PowerShell test
(Invoke-WebRequest -Uri https://yoursite.com -Method Head).ProtocolVersion

When properly configured, HTTP/2 can provide:

html

When working with Windows Server 2012 R2's native IIS 8.5, you'll immediately hit a fundamental limitation: HTTP/2 support wasn't introduced until IIS 10 (Windows Server 2016). The protocol stack in IIS 8.5 simply doesn't contain the necessary components for HTTP/2 negotiation.

Microsoft's supported upgrade options are clear-cut:

1. In-place upgrade to Windows Server 2016/2019: This brings native IIS 10 with full HTTP/2 support
2. Side-by-side migration: Set up new servers with modern OS and migrate sites

Even with registry hacks or component updates, these fundamental blockers remain:

// The SCHANNEL stack lacks ALPN support
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols

For environments where upgrading isn't immediately possible, consider this NGINX configuration:

server {
    listen 443 ssl http2;
    server_name yourdomain.com;
    
    ssl_certificate /path/to/cert.pem;
    ssl_certificate_key /path/to/key.pem;
    
    location / {
        proxy_pass http://your-iis-server;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
    }
}

After implementing any solution, verify HTTP/2 usage with:

curl -I --http2 https://yoursite.com
# Look for "HTTP/2 200" in response headers

chrome://net-internals/#http2
# Chrome's internal tool for protocol inspection

Before committing to workarounds, benchmark these typical improvements:

When ready to upgrade:

• Test all custom ISAPI filters
• Validate application pool identities
• Export server certificates with private keys
• Document all URL rewrite rules