Both IIS and Nginx run on Windows Server, so the “which one” question is decided by your workload, not by the operating system. The short version: if your application is .NET or needs Windows Authentication, use IIS. If you are serving static files, proxying Node.js or PHP, or handling high concurrency with limited memory, Nginx is the better fit. This article compares them across the dimensions that actually matter in production — performance, configuration, security, and ecosystem fit — and ends with a decision checklist. If you are sizing a server for either, our Windows VPS comparison table is a good starting point.
What Each Server Is Built For
IIS (Internet Information Services)
IIS is Windows’ native web server, installed as a Windows role and managed through the IIS Manager GUI, PowerShell (WebAdministration/IISAdministration modules), or its XML configuration store. Its strengths come from being part of the platform:
- Application pools isolate applications into separate worker processes. A crash in one app pool does not take down other sites on the same server.
- ASP.NET Core Module (ANCM) hosts .NET apps in-process with IIS, giving lower latency than a reverse-proxy setup.
- Web Deploy integrates with Visual Studio and Azure DevOps for push-based deployments.
- Windows Authentication plugs directly into Active Directory — no extra configuration needed.
- IIS Manager provides a full GUI for configuration, which matters for teams without dedicated DevOps tooling.
Nginx
Nginx is an event-driven server originally built for Linux, with official Windows builds. One worker process handles many thousands of concurrent connections using an asynchronous, non-blocking model, which keeps memory usage low under load:
- Static file performance is excellent — Nginx serves static assets with minimal overhead, often 2-3x faster than IIS for pure static workloads.
- Configuration is text-based (
nginx.conf), trivially version-controllable. - Reverse proxy and load balancing are first-class features, not add-ons. Nginx can terminate TLS, route to multiple backends, and cache responses without extra modules.
- Memory footprint is smaller — a typical Nginx process uses 50-100 MB, while IIS with default app pools can use 200-400 MB.
Feature Comparison Table
| Feature | IIS | Nginx |
|---|---|---|
| ASP.NET Framework hosting | Native (FastCGI / ISAPI) | Via reverse proxy (Kestrel, HttpPlatformHandler) |
| ASP.NET Core hosting | In-process via ANCM (lowest latency) | Out-of-process via reverse proxy |
| Static file throughput | Good | Excellent — 2-3x faster on pure static |
| Reverse proxy | Via ARR (Application Request Routing) extension | Built-in, no extra install |
| Configuration format | XML (applicationHost.config) + GUI | Plain text (nginx.conf) |
| Windows Authentication | Native (Kerberos, NTLM) | Via LDAP module or AD FS |
| WebSocket support | Native (since IIS 8) | Native |
| HTTP/2 / HTTP/3 | HTTP/2 native, HTTP/3 via Windows update | HTTP/2 and HTTP/3 native |
| Management GUI | IIS Manager | None (third-party tools only) |
| Memory usage (idle) | ~200-400 MB | ~50-100 MB |
| Module ecosystem | Windows-integrated (URL Rewrite, Compression, etc.) | Third-party modules, some Windows-limited |
Performance: When Each One Wins
Benchmarks tell a consistent story. On a 4-core Windows VPS with 8 GB RAM:
- Static files (100 concurrent connections): Nginx serves roughly 15,000 req/s vs IIS around 6,000 req/s. The gap widens with more concurrent connections because Nginx’s event loop does not spawn a thread per request. A single Nginx worker can handle 10,000+ concurrent connections; IIS’s thread pool degrades past a few thousand threads.
- ASP.NET Core (in-process): IIS wins. The in-process hosting model (ANCM) avoids proxying overhead. Latency is 5-10 ms lower per request compared to Nginx proxying to Kestrel.
- Reverse proxy through Nginx to a .NET app: Nginx’s proxy overhead is negligible (1-2 ms per request), and it adds connection pooling, load balancing, and caching that IIS/ARR requires extra configuration to match.
Configuration: XML vs Text
IIS stores configuration in applicationHost.config (XML) and optional web.config files per application. The XML format is verbose but structured, and the IIS Manager GUI translates clicks into XML changes. Nginx uses a single nginx.conf file with a block-and-directive syntax that is compact and easy to version-control. For teams that treat infrastructure as code, Nginx’s config is easier to manage in Git. For teams that prefer a GUI, IIS is the clear choice.
Security Considerations
- IIS runs as a Windows service with a large feature surface. Every installed module (ISAPI, CGI, WebDAV) is a potential attack vector. Disable unused modules during role installation or via
dism. - Nginx has a smaller default surface and fewer moving parts. However, third-party modules compiled for Windows are less battle-tested than their Linux counterparts.
- Authentication: IIS integrates with Windows security natively — Kerberos, NTLM, certificate mapping. Nginx on Windows relies on LDAP modules or an upstream authentication service.
When to Use Each (Decision Matrix)
| Your Workload | Recommendation |
|---|---|
| ASP.NET Framework / .NET Core with in-process hosting | IIS — native ANCM, Windows Auth, lowest latency |
| Static files, PHP, Node.js, Python | Nginx — better performance, lower memory |
| Reverse proxy / load balancer | Nginx — built-in, no extra modules |
| Mixed (.NET backend + static frontend) | Nginx in front, IIS behind — Nginx serves static assets and proxies API calls to IIS |
| Single-server deployment, non-DevOps team | IIS — GUI management, familiar to Windows admins |
| CI/CD pipeline with Git-based config | Nginx — text config that is easy to template |
The best choice depends on your specific stack and team. If you are running a pure .NET workload, IIS is the natural option. If you need high concurrency or a reverse proxy, Nginx adds value. And if you are still deciding on a hosting provider, compare Windows VPS plans to see which ones include the IIS role and which support Nginx on Windows Server.
