What Is a Reverse Proxy and How Does It Work?
A reverse proxy sits between visitors and the server that ultimately handles the request. Instead of the browser talking directly to the origin server, it talks to the proxy first. The proxy then decides where to send the request and what headers to pass through. That pattern powers CDNs, load balancers, and preview tools like HostCheck.
Why Reverse Proxies Matter in Migrations
During a migration, the hardest part is often seeing the new server as if DNS had already changed. A reverse proxy solves that by sending the request to the target IP while preserving the real domain in the Host header. That lets the target server route the request to the correct virtual host instead of returning a default site.
The Basic Request Flow
- The browser requests a URL
- The reverse proxy receives the request first
- The proxy forwards it to the chosen backend server
- The backend generates the response
- The proxy returns that response to the browser
Common Uses
- Load balancing: spreading traffic across multiple origins
- SSL termination: handling HTTPS before traffic reaches the application server
- Caching: serving repeated responses faster from the edge or proxy layer
- Previewing: showing a site on a target server before live DNS changes
The Host Header Is the Key Detail
If you browse directly to a server IP, the server usually does not know which website you want. A reverse proxy can keep the request pointed at the target IP while still sending Host: yourdomain.com. That is why HostCheck can show the correct website where a direct IP request often fails.
Migration Checklist for Proxy-Based Previews
- Confirm the target virtual host exists for the real domain
- Check redirects, canonical URLs, and asset paths
- Verify the homepage is not falling back to a default site
- Test forms and dynamic pages separately if the site relies on sessions or callbacks
Conclusion
Reverse proxies are not just an infrastructure concept for high-traffic websites. They are one of the most practical tools for safe migration work. Once you understand that the proxy controls both routing and headers, it becomes much easier to understand how preview tools, CDNs, and load balancers behave during a cutover.