Nothing at all. It is an extremely capable webserver.
In common with all web servers, advice found via search varies in quality and unfortunately, being Windows based: IIS really suffers. The GUI is pretty intimidating (IIS Manager - both of them) and there are things that can only be done via registry, config files and dark magic.
Fair enough. I'm an Apache, Caddy, nginx, HA Proxy "fan" and I generally only worry about IIS when it hoves into view - Exchange for example, or whatever weird and wonderful nonsense a customer comes up with.
I am almost perversely going to get into IIS but I probably won't. Following logs on Windows is a right old ballache. The bloody things don't seem to get written to disc for quite a while for those many systems that ignore the Windows Events system and dump to .log. I've tried various log viewers. Where the hell is lnav or even less for Windows?
My snags with Windows is opacity. I fire up a daemon on a Linux box and then in another tab/window or whatever, I follow logs - I can use less (is more) or something fancier like lnav. That workflow does not translate very well to Windows.
The taskmanager on Windows is much improved these days - you can now with a GUI work from a network port to a binary (PID) and even associate it with a particular service.
However, text logs are still second class citizens.
Fair disclosure: I administered and developed for IIS fairly heavily in the first decade of my career - not so much by choice, but when you're the star engineer of a three-man contracting firm, you take the jobs that come and learn how to do them on the fly, or else you end up looking for work because your boss went out of business. He didn't, not while I was there, so I guess I must've been good enough at it.
I'm perfectly willing to confide IIS is a fair bit faster, more reliable, and better to work with these days than it was in those - but that's a hell of a long way from imagining it's anything like good.
(Also, a pedant's unrelated note, because I've seen a lot of this in particular lately and I'm going to say something about it somewhere: "hove" is an archaic past tense of "heave", as in the related nautical phrase "heave to," as might be found in a commerce raider's injunction to "heave to and prepare to receive boarders". So something properly is said to heave over the horizon; only after it has done so may it rightly be said to have hove.)
If you already paid for your Windows license, not that much. The way it ties into the OS is a bit concerning to me but, apart from that, it's OK.
I think the question can be formulated in a different way: what's RIGHT with using IIS? What does IIS offer you that other web servers don't? Easy AD integration is the one thing that crosses my mind, and I can't think of anything else besides "it's already there".
If you plan on scaling out, however, licensing costs will grow quickly. If you run .NET Core apps, the built-in HTTP server is very fast and runs on Linux as well. Same story with Spring apps - using Netty/Jetty or even Tomcat is easy and makes your app very self-contained.
I think the big nope for me is that it is from the "Pets" era, before servers were "cattle", which was compounded by containerization and tools like Kubernetes and OpenShift. IIS just doesn't look like it fits into that new model.
It's snobbery to have an opinion? In terms of both static and application web servers I've personally administered nginx, Apache, IIS, Tomcat, Wildfly and Websphere and mention them here in descending order of preference with regard to capability and DX. As you can see IIS falls squarely in the middle of the pack and is actually a distant third in my opinion. The only compelling reason to use it a decade ago was to host .NET applications in an officially-supported manner (and even then it meant contending with licensing, weird logging behavior, arcane MMC-controlled XML-based configuration, Windows Server itself, etc). In the age of .NET Core there's no reason at all.
Of course not and I didn't say any such thing. The original comment "People use IIS?" is clearly a passive-aggressive dig at MS, its tech, and those that use it (as is so often the case in tech circles). It's quite pathetic and childish. If I misunderstood that, then I apologise to the author, but I'd argue it still adds nothing to the discourse even if it was asked honestly.
It doesn't mean you can't hold an opinion on the relative merits of any one piece of tech. But this "my computer is better than your computer" immature schoolboy nonsense is pervasive in tech circles and is extremely tedious.
I have no love for IIS, but it's a perfectly capable webserver and is clearly still used. The idea that the .NET world have all moved over to .NET Core is also a wishful one unfortunately, I still maintain my open-source libraries for the legacy framework as I know there's plenty of places that can't just 'flip the switch' to .NET Core. It's not quite as bad as Python's V3 moment, but it's up there.
> "People use IIS?" is clearly a passive-aggressive dig at MS
Feels a bit snarky, but not too aggressive. Windows is not a popular choice for cloud platforms and those users seem to be overrepresented here. I can imagine someone being genuinely surprised it's used for more than serving documentation that's already on a Windows server.
That said, as I mentioned earlier, it's hard to find a use case where IIS (or Windows) is a better choice than any of the popular open source http servers and app platform runtimes.
There is a colossal corpus of .NET Framework code out there and I wouldn't be surprised it achieves the status of COBOL (but with a lot less charm) at some point in the future - where code on it is maintained ad infinitum even though almost nobody would deploy a greenfield app using it.
In common with all web servers, advice found via search varies in quality and unfortunately, being Windows based: IIS really suffers. The GUI is pretty intimidating (IIS Manager - both of them) and there are things that can only be done via registry, config files and dark magic.
IIS gets a lot of undeserved stick in my opinion.