alt.hn

5/13/2026 at 3:09:52 PM

The limits of Rust, or why you should probably not follow Amazon and Cloudflare

 https://kerkour.com/the-limits-of-rust

by randomint64

5/13/2026 at 3:36:33 PM

Lots of tortured logic in this post.

1. You shouldn't pick a programming language the team doesn't know. That's common sense, not an argument against Rust.

2. Rust ranks lower on the most used languages list because it's newer than Java, Python, C, and all of the others higher on the list.

3. You don't need to use async Rust. If you do, I disagree that it's as hard as this is implying, but I would agree that it's not as easy as writing sync code.

4. Rust projects don't decay like this is saying. Rust has editions and you can stay on an older edition until you're ready to port it forward. My experience with jumping to a new Rust edition has been easy across all projects so far. It's funny that they argue that adding new features to the language leads to unmanageable complexity, because the very next topic argues that the standard library doesn't have enough features.

5. If you want a batteries-included standard library I agree that you should pick Python or Go instead.

Most of the blog is an ad for the author's book. I was hoping this post had some substance but I think they chose the title first to attract clicks for the book ad and then tried really hard to find some content for the article second.

by Aurornis

5/13/2026 at 7:53:37 PM

> You shouldn't pick a programming language the team doesn't know. That's common sense, not an argument against Rust.

Actually if your team doesn't know any suitable languages it could make sense to pick Rust because they will cause far fewer accidental fires in Rust.

(Safe) Rust is much more forgiving of "I didn't know that's how computers work" than a language like C or C++ yet it's as close to the metal as they are which may matter for your application.

If you're hiring programmers they probably already know some suitable languages which should strongly influence your choice, but if the team's main expertise is not programming they may take to Rust much easier than you'd expect.

by tialaramex

5/13/2026 at 5:41:22 PM

> 3. You don't need to use async Rust.

Technically correct, but… Want to build a web app, every more or less popular framework is async. Want to make a web request? High change of async. Database? Very likely async, too. A huge fraction of crates are async. Right now crates.io says there are "54172 reverse dependencies of tokio”. And the page that lists them struggles mightily to load. And that’s only direct dependencies of tokio, no indirect ones, no dependencies on other runtimes, no generic dependents.

by pointlessone

5/13/2026 at 6:00:42 PM

And all the popular ones include a synchronous interface you can use instead of the async one. If if they don't, you can wrap your calls in spawn_blocking.

You might complain about it pulling in tokio, but that's a very different complaint than having to learn/use async.

by bryanlarsen

5/14/2026 at 8:32:17 AM

Is the inclusion of synchronous interfaces a new thing? When I learned actix_web 2-3 years ago for some webservices at work, the documentation surely (at least) started of with async functions everywhere. Did that change? Were synchronous interfaces introduced later in the actix_web documentation? Or did everybody switch over to axum in the meantime and axum has synchrounous interfaces!? (I just checked and according to crates.io axum seems to have 8x the recent downloads of actix_web.) background: actix_web is still the only Rust webframework I have experience with

by simon_void

5/13/2026 at 5:56:42 PM

> Want to build a web app, every more or less popular framework is async.

I think its the same as Java, Tomcat has some async threadpool inside, they just hide it from you, and your favorite rust framework doesn't, you need manually move your sync logic to Tokio spawn_blocking

by andriy_koval

5/13/2026 at 4:13:59 PM

For the use cases the author is alluding to, you do need to use async. Non-cooperative threaded multitasking isn't a real choice for backends, and Rust doesn't have virtual threads.

Before Java got virtual threads in Project Loom, people were typically using some promises equivalent even though it mangled the heck out of all your code, cause they didn't want to be doing blocking stuff with a thread pool. That was a big motivator for Go and Kotlin coroutines, and why Rust and Python put so much effort into adding event loops after the fact.

by traderj0e

5/13/2026 at 4:39:34 PM

For that matter, even if you do use async, if you're writing a service based app (such as web services), IMO, you'd probably just want to center on tokio and axum, then stick to the tokio ecosystem. The main reason it's not a blessed standard library thing, is that Rust can scale down into embedded systems usage, and you aren't going to use something like Tokio there... that doesn't mean you shouldn't just use what everyone else does at a higher level application.

Also, in regards to OP's reference to changes to Rust, it's not changes/additions or bug fixes that should be a concern, it's the number of breaking changes. For a contemporary counter example, look at how much C# has changed since the .Net Core fork started out... They're on version 11 now (skipped v4), and that doesn't count the library sub-version shifts along the way. And a lot of critical banking infrastructure is written in and running on it (as well as Java). Your money is literally relying on it.

by tracker1

5/14/2026 at 5:58:14 AM

> And a lot of critical banking infrastructure is written in and running on it

How much of that critical infrastructure runs on .NET Framework as opposed to the latest .NET Core though?

by SkiFire13

5/14/2026 at 6:47:10 AM

IME: less than you’d think. I know one major C# project that’s only half completed its migration and that huge (both in terms of what’s been achieved and what still needs doing). There’s another that keeps it for the front end because it runs on >10,000 client machines. All the others, big or small, have migrated with small carve-outs for stuff .NET Core doesn’t and probably never will support.

by moomin

5/14/2026 at 6:47:54 AM

From recent experience I'd put it slightly higher on the old framework, but plenty of new dev on v5+ and I think sticking on framework is worse at this point.

Though I would say that breaking changes since Core 3 have been pretty limited. V5 unified .net under the new core as the path forward for framework users as well.

by tracker1

5/14/2026 at 6:46:26 AM

This take on native threads sounds overly pessimistic. 99% of backends do fine with the nr of native threads you can easily run in a single process at least on Linux. Not sure what the practical limit is now but 10k used to be no problem many years ago.

(eg 100k threads in 2002: https://lkml.iu.edu/hypermail/linux/kernel/0209.2/1153.html .. where the 32-bit 4 GB limit seemed to be the main obstacle)

by fulafel

5/13/2026 at 6:17:11 PM

> Before Java got virtual threads in Project Loom, people were typically using some promises equivalent even though it mangled the heck out of all your code

I think majority Java code is just sequential blocking code, and it works just fine.

by andriy_koval

5/13/2026 at 5:08:38 PM

Rust had that, but decided it wasn’t a good enough fit. Which was the motivation to keep exploring and land on the current async implementation which scales from embedded to servers with minimal overhead.

History:

This RFC proposes to remove the runtime system that is currently part of the standard library, which currently allows the standard library to support both native and green threading.

https://github.com/rust-lang/rfcs/blob/master/text/0230-remo...

by ViewTrick1002

5/13/2026 at 5:57:46 PM

well rust async is 'still evolving' right now

it's better than being stuck, but it's not '100% polished' right now (though some crates do make the experience somewhat more polished: especially dtolnay's crates)

by sysguest

5/13/2026 at 6:09:07 PM

Agree. There's stuff missing, and there are problems which likely are "multiple Phd theses" level to solve cohesively. Either in Rust or a successor language when the problem space has been explored.

For me the most annoying part are the footguns async Rust introduces, which Rust generally is blessedly empty of compared to e.g. Go or other languages.

Like for example, cancellation safety, dealing with "long running" futures, cleanly terminating a program, deadlocks at a distance [1] and others I'm forgetting now.

[1]: https://rfd.shared.oxide.computer/rfd/0609

by ViewTrick1002

5/13/2026 at 4:31:17 PM

> why Rust and Python put so much effort into adding event loops after the fact.

Perhaps Python, but Rust went the other way - it had all that stuff built and it was removed.

by jen20

5/13/2026 at 4:37:53 PM

Er yeah technically the event loop isn't part of Rust, just the async/await syntax. But it's implied that you're going to use some event loop with it.

by traderj0e

5/13/2026 at 4:41:26 PM

No, it's implied that you're going to use some sort of async runtime with it... said runtime can be simple real threads, a thread pool or virtual threads and there are implementations for all of them. And even then, it's super easy to start a new real thread in rust, around any async runtime.

by tracker1

5/13/2026 at 4:17:24 PM

> Between January 2020 and May 2026 Rust has seen 54 releases, which amounts to 7500 lines of changelog. > During the same period, there was 12 Go releases, 12 Node.js releases (but only 2 LTS) and 5 Python releases.

Some corrections:

Rust saw 54 (I assume that's correct, I didn't recount) minor releases, with a few minor breaking changes. If we only count editions there were 2 releases, but again those don't break backwards compatibility.

Python saw 5 major releases, each breaking backwards compatibility. Counting all releases they had 132.

Node has an LTS every year. There were 6 LTS versions in the last 6 years. Those releases also included major breaking changes.

Go had no new major version, like rust it's only made minor changes.

So going by the author's own evaluation, rust and go are considerably better for project decay.

> For example, I just looked at the dependencies of a small project I'm working on, and we have 5+ (!) different crypto libraries: 2 different versions of ring, aws-lc-rs, boring, and various libraries from RustCrypto

ring is explicitly an experiment, not suitable for use. My guess is the author looked at their Cargo.lock to determine what duplicated dependencies they have.

For the uninitiated, rust libraries can have optional dependencies that only get included under certain conditions. A common pattern is for a library to support multiple underlying implementations, such as different crypto libraries. For instance rustls has both ring and aws-lc-rs as optional dependencies, meaning that both get included in the Cargo.lock file when resolving dependencies. That doesn't mean that both are actually being used.

by ben-schaaf

5/13/2026 at 4:20:11 PM

Ring is a de facto standard for better or worse. In our codebase we basically have no choice but to use it

by aabhay

5/14/2026 at 7:03:09 AM

Yeah on top of that I've seen virtually no evidence that Rust projects really decay. I bet you can compile some really old Rust projects with the latest Rust with no problems.

In my experience the "oh god I have to compile a 10 year old program" dread hierarchy (from least to most dread) is:

1. Go. Very reliable.

2. Rust. Also very reliable.

3. C++. Sometimes stuff breaks, e.g. when they change the default C/C++ version and dependencies don't specify it. That happened to me recently.

4. Python. They deprecate stuff all the time that is often actually used (e.g. a load of stuff in pkgutil recently).

5. JavaScript. Good fucking luck.

by IshKebab

5/14/2026 at 6:55:56 AM

Every single one of this authors articles that I've read (and it's a fair few), are poorly argued, and generally incorrect. It would be easy to engage and disprove, but it's better not to give this air. Just say no to kerkour.

by joshka

5/14/2026 at 8:06:41 AM

"Rust's biggest weakness: an anemic standard library"

As someone who programs in both go and rust, I could not agree more.

by throwa356262

5/14/2026 at 5:42:44 AM

Yes, Rust should not be used for everything, like any other language shouldn't, but some devs only see nails.

Example Amazon uses Rust mostly for actual systems programming, writing hypervisors and cloud infrastructure low level services.

They have plenty of other stuff in there as well.

by pjmlp

5/13/2026 at 3:53:50 PM

A common thread I see in this, and other articles of its kind, is that rarely do they come out and say what kind of project they are working on, leaving the headline to sound generically applicable. I can make some guesses, given the emphasis on async, that they contrast with Go, and the mention of systems programming as an exception. But after enough of these, one would get the impression that Rust is primarily a backend language, competing with other backend languages, that happens to also be good for systems. I'm not sure that is even the use case driving corporate adoption.

by egorelik

5/13/2026 at 4:50:28 PM

The big driver for corporate adoption is that this is probably a Silver Bullet in the sense meant in "No Silver Bullet". An order of magnitude improvement for software engineering.

I think the sort of person who figures they don't need to read the book because the title told them there was a Murder on the Orient Express believes Brooks says that it's just all irreducible complexity, too bad, stop looking. In fact "No Silver Bullet" says nothing of the sort and we would be astonished if, after so much time, literally none were discovered.

There are plenty of domains where Rust makes sense if you could just choose Rust, but probably doesn't make enough sense that you should retrain or even re-hire a whole team. Google spends money training devs who don't know Rust, because it's getting enough value out that it makes sense to do that, your web slinging business running on razor thin margins is probably fine in PHP or whatever and should not buy Rust training.

by tialaramex

5/14/2026 at 6:33:31 AM

In fairness, the post specifically mentions Amazon and Cloudflare, which are using Rust largely for backend stuff (though also for lower-level systems-y stuff, and I think Go is also a favored backend language at Cloudflare). But yes, other large tech companies (Google and Meta come to mind) are using Rust primarily for the lower-level systems-y stuff, where Go isn't an option and the alternative to Rust is C++. These applications are also less likely to need async and so don't have to deal with that set of rough edges.

by ameliaquining

5/13/2026 at 4:22:52 PM

The article should've been clear about use cases. I think the reason for the focus on backends is because that's where people keep randomly wanting to rewrite in Rust.

by traderj0e

5/13/2026 at 3:49:50 PM

This is a bizarre article, and it kind of reminds me of the concept that the only truly good software is the software you've never used.

by cbsmith

5/14/2026 at 6:02:49 AM

It's not mentioned, that the language itself is designed in such a way, so it requires a lot of boilerplate involving traits. The same results (both safety and speed) are achievable without using traits at all but by relying on duck-typing.

by Panzerschrek

5/13/2026 at 4:11:03 PM

Is async in Rust really this bad? Last time I used Rust was before that existed. I know it's a pain in Python because they bolted it on way after, but in JS it's a breeze because everything standardized on promises early.

by traderj0e

5/13/2026 at 4:36:17 PM

> Is async in Rust really this bad?

No, it's not. It works. Perfect? No, absolutely not. There is plenty you could improve, plenty of rough edges you could smooth out. Stuff that caused us problems at the job I had writing low-ish level machine control services. But it's totally workable and we were able to ship working devices, especially compared to doing async stuff in other most other languages, especially the memory-unmanaged ones.

Kind of like Rust itself, a ton of people have tried it and bounced off it because they couldn't get it working in 10 minutes, and in doing so have declared it impossible/for geniuses only/broken/ecosystem-destroying. The narrative around async Rust is probably 70% meme/bad PR, 30% real, actual issues that could be improved.

I hope this comes off as fair. I don't want to excuse any of the shortcomings, but it's a working, useful tool.

by asa400

5/14/2026 at 6:41:10 AM

I think part of it is that most of Rust sets a really high standard for polish and good design; developers new to the language are often quite impressed by its expressiveness and by the breadth of bug classes it protects you from, once you get over the initial learning curve. (Not always—some developers never grow to like it, either because it's a bad fit for their use case or because they happen to find its particular forms of ceremony especially off-putting—but the success cases are striking.)

And then you start using async, which is less polished and has more awkward design compromises and more footguns that you only find out about at runtime, and it's a bit of a disappointment by comparison, even if some of the problems aren't worse than what you find in competing languages. This is the vibe you get in the Oxide RFDs about things like futurelock, for example.

by ameliaquining

5/13/2026 at 11:43:35 PM

100% agree with your take, speaking as a professional async rust writer for like five years now.

I’ll add to it that structured concurrency patterns in async Rust can be legitimately awesome and very fun, once you’ve bounced off the traits in the futures crate enough times to use it in anger. The type system can be annoying, but as usual, it’s almost always technically right, and once you understand the ownership flow required for your nifty chain of future combinators, is not too too bad.

by mplanchard

5/13/2026 at 4:47:50 PM

Funny... I started off with very little knowledge, totally cheated with what I wanted to do by cloning everything crossing various library boundaries and it still worked surprisingly well. Then I learned about (A)RC, Box etc... and I still kinda really hate the lifetime syntax.

Note: most of what I've used it for has been relatively simple... API's with tokio and axum in rust are emphatically not much more difficult than say C# with FastEndpoints, or JS/TS with Hono. It's a bit different.

by tracker1

5/13/2026 at 4:24:52 PM

Rust’s async makes some design decisions that make it a unique feature: no other language has zero allocations to do async, for example. (In C++’s version you can get it to do no allocations if you do certain things, like making the required allocator a no-op, in my understanding, but it conceptually requires a call to an allocator)

This makes it suitable for a much wider variety of tasks than other languages with similar features, but does mean that there are more details that you need to care about than in other languages that are higher level.

This means it is controversial: some people would prefer a higher level experience, but for those who do use it for its full range of tasks, it’s great.

There are some rough edges, but it’s just a feature that, even outside of Rust, some people just fundamentally dislike. So it draws a lot of heat from all sides.

It is also probably the single largest driver of adoption of the language. Rust started truly taking off once it landed.

by steveklabnik

5/13/2026 at 4:52:19 PM

I can only speak for myself, but I kind of refused to get started with Rust until async landed... only because it's kind of a core of scalable services. I think it's pretty great in that you can use an async runtime, but still launce native threads if you want/need to for specific scenarios. It's pretty great and for most high level tasks, I wouldn't classify it as significantly more difficult than C#.

A few other things I've done with it have been written by AI as much as myself... which has similarly been pretty nice... Rust code can be very easy to reason with (lifetime syntax not withstanding). For some reason Rust lifetimes burn my soul.

by tracker1

5/13/2026 at 4:30:09 PM

"it’s just a feature that, even outside of Rust, some people just fundamentally dislike" is why I have a hard time gauging this. I know Python users whine about it endlessly just because it's a feature from JS, even though Python's existing concurrency features were the worst of both worlds.

The Rust-specific async sounds interesting. I should give it a try.

by traderj0e

5/13/2026 at 4:38:21 PM

If someone finds normal ownership concepts in Rust to be difficult, making the leap to async is only going to make that worse.

I don't think it's friendly to Rust beginners but I also think the complaints about if have been overblown

by Aurornis

5/13/2026 at 4:54:24 PM

I think it depends on what you're doing... getting to a point where you understand Arc helps a lot, and if you're mostly using it with something like Axum, there's very little you need to worry about specific to lifetime or a lot of the burrowing logic in practice. You can definitely get by with less than perfect code.

by tracker1

5/13/2026 at 5:11:00 PM

[dead]

by Aurornis

5/13/2026 at 4:15:43 PM

No it’s not bad at all. If you’re creating a library you might run into some hard problems, but for application code it’s pretty easy.

by nothinkjustai

5/13/2026 at 5:27:28 PM

This is the case, when author argues about the right thing (you do not need Rust everywhere on every project and in every feature, especially if your team has 0 prior exposure to Rust or at least C++), but provide very awkward arguments which are not aligned with core thesis.

by vld_chk

5/13/2026 at 3:56:21 PM

I don't have a problem with this post, in fact I think it fully redeems any criticism by describing the stronger use cases for the language.

Takeaways:

If picking an arbitrary language to learn, if you are building small-to-medium scale things that require async, rust is not the first thing to reach for.

The stdlib and the package ecosystem is a mess.

---

Use if:

If you need gigascale performance and have the resources to learn it and deal with the complexity of async.

If you are writing performant global OS libraries.

If you are writing IoT and want something with more protection than C.

by unethical_ban

5/13/2026 at 3:49:30 PM

This gets so old. Rust is a programming language. It does some things really well, some things less so. It isn't a panacea, it's a tool. People can use it because they like it, right-tool-for-the-job or not. People can hate it, hating a programming language is one of the most benign things to hate in the whole world. "Language-ist" is a world I never want to live in.

Feels like there are some people who love rust, and some people who hate rust, and most everyone else doesn't give a shit. Everyone is right and everyone is wrong, depending on who you ask.

Can't we just go back to the emacs vs vi debate? Is that the itch people are trying to scratch?

by irishcoffee

5/13/2026 at 4:06:05 PM

The post doesn't hate on Rust, it's more saying you probably shouldn't use it for high-level code like a web backend. Which is pretty reasonable.

by traderj0e

5/13/2026 at 4:22:52 PM

I have been churning away writing a custom backed in rust using Dioxus, it is excellent for this kind of high level work.

by vablings

5/13/2026 at 5:00:09 PM

Having written web backends for three decades in quite a few languages along the way, I disagree. You can definitely write some relatively simple backends in Rust. Tokio and Axum make it quite friendly, and depending on what you are connecting to it becomes super easy, barely and inconvenience.

Even if you cheat and do a lot of cloning across library boundaries, it's still likely to perform pretty well compared to a lot of prevailing frameworks. I'd say I'm most recently most familiar with C# and FastEndpoints as well as TS/JS and Hono, but I've used many others. I've also done a bit with Rust and Tokio/Axum and it's not been significantly worse than the former mentioned options. That said, the runtime containers are a fraction of the size, start significantly faster, and use a lot less memory with Rust. And once your boilerplate is in place (jwt/oauth, db context, etc), it's roughly the same work.

by tracker1

5/13/2026 at 3:59:11 PM

vi would be much easier to rewrite in Rust.

by mwigdahl

5/13/2026 at 5:22:35 PM

Helix is in fact written in Rust and is now a frequent contender in the editor wars.

by NoboruWataya

5/13/2026 at 4:18:21 PM

The annoying thing about Rust, or at least the hype around Rust, is that people want to in use it for bloody everything.

We have absolutely no need for it at work. We're writing micro services that run in K8s with no extreme performance requirements. Nobody on the team knows the language (I know it better than the people arguing for it, and I don't know more then the basics). And yet, every couple of weeks, I'm having to talk someone out of switching certain services over to it. It's like a damn disease.

by scuff3d

5/13/2026 at 4:24:39 PM

Because the attraction of rust is powerful. The same toolkit allows you to write code for a microcontroller or a full fat arm webserver, the rules are the same and the language is strong.

The best bit about writing rust is the reason why it kinda sucks for corporations. You can "finish" your code

by vablings

5/14/2026 at 5:05:30 AM

also some of those people probably wanna put "used rust at work" on their resume

by deepriverfish

5/13/2026 at 4:59:21 PM

Thank you for so aptly demonstrating what I deal with at work.

by scuff3d

5/13/2026 at 5:00:06 PM

Fair points, but this glosses over some of the not-great parts. Cargo isn't great. No sanctioned formal spec isn't great. Compilation times aren't great. Messing around with wrapping foreign types can be a bit of a bear sometimes.

It's a fine language, just like all the others. I'd rather write a web server in Go and a use C when targeting a micro-controller.

Almost reminds me of a quote I heard about python a long time ago: python is the second-best language for everything, and the "first-best" for nothing.

by irishcoffee

5/13/2026 at 9:32:55 PM

Sure, and that's probably because you are good with both Go and C. for me, I use rust as the hammer, and everything is a nail. Hobbyist vs Employee I guess

by vablings

5/14/2026 at 6:19:27 AM

Except rust is way more productive than any other language out there...

by _davide_

5/13/2026 at 4:34:38 PM

It's a rehash of a bunch of old misconceptions. I thought we've buried these when people got actual experience with Rust.

The dumbest one is counting changelog lines. Have you even read them? These days most of them are "obscure libstd function is now allowed in const contexts".

The regular Rust releases include compiler improvements, libstd evolution, and build system tweaks. Nobody's saying C keeps changing because LLVM has a long changelog or CMake added a new feature.

by pornel

5/13/2026 at 5:28:31 PM

I agree but more common than "Now allowed in const context" is "This new type/method/free function is now stabilized" e.g. in 1.95 they stabilized a bunch of "Atomic update" methods such as:

AtomicPtr::update which is a nicer way to write one of those "Get the pointer, do some stuff to calculate a new value from the old one, then try to swap its old value for the new one, if the pointer changed meanwhile repeat each time with the changed value until we succeed" stanzas some low-level people will have written a hundred times. This library feature does all that boring boilerplate for you, you just write that "calculate a new value" code as a lambda (or function, Rust doesn't mind) and you're done.

That's the sort of feature where if it didn't exist when you wrote your code, you go "That's nice" and move on, no change needed, but now that it does exist you might use it in future software you write. If you have a team writing Rust it probably makes sense to have somebody read these changelogs, but that's about it.

by tialaramex

5/13/2026 at 4:17:31 PM

Weird post. One could pick any language OP recommends over Rust and find just as many if not more reasons not to use it.

by nothinkjustai

5/13/2026 at 4:12:23 PM

Nobody has ever seen or heard Wesley Wiser talk. Supposedly he's the rust compiler team lead. I claim he's an NSA front end. Prove me wrong.

There is no reproducible build of the official rustc binary. They claim they're using a modified version of LLVM.

I am moving my projects to Cangjie, I no longer trust _any_ American piece of software.

by gamander2

5/14/2026 at 6:41:51 AM

Lol, use Gentoo

by _davide_

5/13/2026 at 8:12:33 PM

Why don't you just compile rustc?

by fluffybucktsnek