How Meta patches Linux at hyperscale

https://thenewstack.io/how-meta-patches-linux-at-hyperscale/

by elorant • 3 years ago

135 91 3 years ago

fragmede4• 3 years ago

Ksplice is the original live patching technology that got bought by Oracle and was later extended to user space programs while I worked there. It's a really neat technology that isn't made obsolete by the move to cloud, since you still don't want to have to restart the whole fleet at scale.

metadat• 3 years ago

What's the live app patcher called?

fragmede4• 3 years ago

I have objections to the name, but it goes under Ksplice for User Space.

https://blogs.oracle.com/virtualization/post/ksplice-zero-do...

ravenstine2• 3 years ago

Never heard of this "hyperscale" concept before. How is this any different from... scaling?

mc32• 3 years ago

Supermarkets and super cars aren't enough. We need hypermarkets and hyper cars to be current. So now we can’t just scale, I guess that’s for trucks, so to be current you need hyperscale.

froh• 3 years ago

Cybertruck and cyberscale?

(I'm joking)

phyrex2• 3 years ago

https://en.m.wikipedia.org/wiki/Hypermarket ¯\_(ツ)_/¯

kevindamm• 3 years ago

give it a couple more years, we'll have ultrascale

wmf• 3 years ago

In general every order of magnitude brings new challenges. Companies running over a million servers have a lot of problems that smaller ones don't. Also they just have more room to amortize R&D.

revskill• 3 years ago

Universe scale i guess.

adaml_623• 3 years ago

Size of the entire universe man

tester7563• 3 years ago

https://en.wikipedia.org/wiki/Hyperscale_computing

zug_zug3• 3 years ago

In computing, hyperscale is the ability of an architecture to scale appropriately as increased demand is added to the system.

So yeah just scaling. I agree I've never heard the word "hyperscale" before and don't think we need that extra intensifier for a well-understood idea.

phyzome2• 3 years ago

Yeah, and this isn't a problem that interacts with scale. If you can patch 100 servers with an automated method you can patch 1,000,000 of them.

agrajag• 3 years ago

This is absolutely a problem that interacts with scale. With 1M servers you’re almost certainly dealing with hundreds of service owners, and some of those are going to need additional features you don’t have to worry about with 100 servers. Some examples are databases with graceful failover, long running AI model training jobs, or distributed databases like etc where you have to be mindful about how many can be down at a time.

It’s not 10,000x harder to patch that 10,000x more machines, but it’s not 1x either. Easily 10-20x harder, if not more.

comprev• 3 years ago

The "H" in ADHD stands for "hyperactivity". This implies _significantly_ more activity than the norm to a point where they really stand out.

In sci-fi a spaceship travelling at "hyperspeed" was perceived to be so much faster than anything known to man that it would be difficult to comprehend.

The performance and cost of a hypercar compared to the average family car is sometimes difficult to understand too. The average person would have to work (potentially) hundreds of years to afford a €10M hypercar.

"Hyperscale" is so large that even us working in tech have difficulty grasping it because we have nothing tangible to compare it to. A million servers is bind boggling to me even with the "cattle not pets" mindset

rthnbgrredf• 3 years ago

I dislike the term 'hyperscale' as it lacks concrete meaning. We need a metric akin to kilobytes or megabytes for storage. Terms like 'kiloscale' and 'megascale' could better indicate the scaling range of a service. For instance, scaling a service to a thousand instances and back to zero or rolling out patches to thousand instances could be termed 'kiloscale'.

ravenstine2• 3 years ago

That's why I brought up the question, and I'm baffled why so many people have been downvoting it. To me, its use seems very specific yet nothing I read about it told me anything concrete. From what I can tell, it actually is meant to broadly mean the extreme end of scaling. The threshold is still unknown to me, but I'll just take it that Meta is hyperscale.

hellozomo3• 3 years ago

"Draining and un-draining hosts is hard."

I'd stop right there and fix that, because that's a bullshit reason. Cycling hosts in and out of service is easy unless you're not doing things properly.

The Linux kernel is simply not designed to be live patched and it's a total hack to try to do it, it will never work 100% of the time, always be a source of uncertainty, and always be expensive in terms of engineering work. Disaster will always be looming.

By contrast, fixing their system for taking hosts in and out of service, so that it's extremely robust and reliable would likely pay big dividends in reliability.

My guess would be that this approach is papering over organizational dysfunction. One team can patch all the kernels but one team can't make all the hosts support proper cycling in and out of service. And no one cares to fix it because there's no real incentive to do so. Only cool hacks and new projects are properly rewarded.

extr• 3 years ago

My guess would be that this approach is papering over organizational dysfunction.

So what? At large enough scale organization problems are harder than technical ones: if you can fix the former with the latter, that's still a win.

hellozomo3• 3 years ago

But it's not "fixing" the problem, it's papering over the problem by piling tech debt on top of tech debt.

Framing this like it's a good thing is my only objection.

tysonfurytoo• 3 years ago

It may be easy to cycle hosts in and out, but it can also be time consuming, apparently. In the article it mentions taking 45 days to patch all hosts. The article also points out that this is too long for security updates.

Nothing will work 100% of the time. If their patching mechanism is thoroughly tested and battle hardened, I think the risk would be acceptable. Once you do the initial kpatch security upgrade, you could even schedule the machine for serivce so that it's not relying on that, limiting your exposure to bugs.

WookieRushing• 3 years ago

Why do you think its easy?

There's a lot of systems where you can easily take down some hosts, but taking down more than N% at a time causes issues. If your fleet is large enough then you are limited by the largest set of hosts where you can only take N% down at a time. Now you could say keep the sets of hosts small or N% large. But that can cause other issues as you typically lose efficiency or zonal outage protection.

A solution to this could be VM live migration or something similar. This breaks down for storage systems where you can't just migrate those disks virtually since they're physical disks or places that don't use VMs.

natbennett2• 3 years ago

The work that makes cycling hosts in and out easy is itself hard.

I agree that it’s the right thing to do but it’s hard.

fragmede4• 3 years ago

It's not a bullshit reason. You can put all the lipstick you want on the pig and put software all around it to make it all sorts of easy, but at the end of the day, having to reboot is a stop-the-(machine's)-world situation. Not having to do that is just better. Even if it doesn't work 100% of the time, that's still better than having to reboot the whole fleet. 45 days to reboot the whole fleet!

Throwing FUD and saying disaster is looming because its scary computer magic (out of MIT) was a scare tactic RedHat used to throw around about Oracle/Ksplice until they developed their own (Kpatch), then suddenly their sales team had to backtrack and say actually hot patching is good and can be trusted. I'm not saying it's not risky or dangerous, it's operating in kernel space, but that's why they pay really smart people to be careful when doing it, and not digital equivalent of a plumber who can't do more than glue libraries together.

A better understanding of the underlying technology so it's less magic might assuage your fear of it, but thinking Facebook is so dysfunctional that they haven't already made it easier to reboot is to misunderstand the problem at hand.

mypalmike2• 3 years ago

fixing their system for taking hosts in and out of service, so that it's extremely robust and reliable would likely pay big dividends in reliability.

Facebook hosts can be robustly cycled. Of course. They've been doing this stuff for years. They've figured it out. That's not the issue.

Scaling up brings about new problems. This article specifically mentions the 45 day rolling restart issue. That's not an issue when you have 1000s of servers. It's one that shows up a couple of orders of magnitude later.

So you either solve the problem with a hack like kernel patching or you work to reduce restart times (drain + shutdown + OS restart + process initialization across every service). Get those restart times down 50% (good luck accomplishing that) and congrats, you're down to maybe a 25 day rolling restart, which is still quite a problem.

hellozomo3• 3 years ago

What exactly do you think requires cycling millions of hosts to take 45 days? That's a couple hundred hosts every five minutes across a large number of datacenters?

I wouldn't expect it to be halved by optimization. I'd expect it to be an order of magnitude faster and take more like 4.5 days.

I wouldn't be surprised (but I would be impressed) if they tried and got it down to a full cycle requiring one working day. That's around 1% of hosts cycling every five minutes.

raincom• 3 years ago

Redhat provides kpatches for 6 months, that's all. If you are running a year old kernel, no kpatches are provided for that kernel. Definitely, one needs to recycle hosts every six months.

lokar• 3 years ago

At google we did pretty much the same thing. Aimed to be able roll a kernel in 30 days, but various edge cases always made it drag out at the end unless you really spend a lot of human time on it. So use kaplice for really critical stuff (where the patch was easy, not always the case).

A reasonable compromise in the real world.

ungamedplayer• 3 years ago

At redhat, we just maintain kpatch and hire kernel engineering to do the same. Turn around is about a week for 40 variants of kernel.

jb_gericke• 3 years ago

Yeah, especially with containerisation and orchestration / Kubernetes, I get that perhaps not everything is viable to containerise, but in 2023 this feels archaic and like a lot of (potentially unnecessary) engineering work.

faitswulff• 3 years ago

So, if you’d rather not have downtime with your servers, data centers, and clouds, follow Meta’s example and use live patching. You’ll be glad you did.

Most orgs don’t need and won’t benefit from emulating Meta for the sake of emulating Meta.

baby_souffle• 3 years ago

Most orgs don’t need and won’t benefit from emulating Meta for the sake of emulating Meta.

SO. Much. This.

Worked at more than a few places where the stack had almost as many layers as it had engineers "because this is how we did it at FAANG..."

Right, and those places also had a few orders of magnitude more engineers on staff to support it all. We do one hundredth of the things FAANG does and we have less than 50 _total_ people in the company; the simpler the stack, the better.

influx• 3 years ago

Likewise at Meta there's a bunch of cargo-culting from Google.

phyrex2• 3 years ago

Could you expand please?

nickysielicki• 3 years ago

This sort of criticism gets repeated all the time ("Google designs for Google scale, but you're not Google, so don't use kubernetes!"), and sometimes it's fair, but this doesn't really make sense to me on this particular article.

If the infrastructure exists within your org's distribution of choice to do this, it's basically all upside. On AL2023, you just do:

`sudo dnf install -y kpatch-dnf kpatch-runtime`

`sudo dnf kernel-livepatch -y auto`

`sudo systemctl enable --now kpatch.service`

Super simple, one less thing to worry about.

ies7• 3 years ago

Super simple, one less thing to worry about.

We got bitten by kpatch a few times before decided to abandon it around 2017.

From kpatch github (2023):

WARNING: Use with caution! Kernel crashes, spontaneous reboots, and data loss may occur!

imetatroll• 3 years ago

The danger in your comment is that people who are primarily "working" because they want to play on someone else's dollar with some new, frivolous tech - from the perspective of what their business actually needs - are going to be insulted by this. Good luck.

TheAceOfHearts• 3 years ago

I wish they mentioned how long a full deployment takes Meta using this method, that seems like an important detail to omit.

So, if you’d rather not have downtime with your servers, data centers, and clouds, follow Meta’s example and use live patching. You’ll be glad you did.

Maybe if you're working at Meta's scale it makes sense... But I think most well designed services and applications should be able to get by just fine with a full reboot of any single server. I can't really fathom the complexity of managing millions of servers though.

sweettea• 3 years ago

https://youtube.com/watch?v=ILTqn1EYIXQ is the original talk, which says it takes 4 days to deploy a KLP to the whole fleet.

mattboardman• 3 years ago

There's more in-depth information on that subject here:

https://www.usenix.org/conference/osdi23/presentation/grubic

cortesoft3• 3 years ago

Maybe if you're working at Meta's scale it makes sense... But I think most well designed services and applications should be able to get by just fine with a full reboot of any single server.

I feel like this should be the opposite... I don't work at Meta scale, but I do work for a CDN with 10s of thousands of servers, and everything we do is based on the idea that some machines will always be going down, because some hardware is going to fail every day just from probability. You have to design everything for failure.

Given that, it shouldn't be hard to take servers out of production for patching and updates.

In other words, a hyperscaler is going to have less incentive to minimize down time than smaller shops.

vbezhenar• 3 years ago

I don't follow. Reboot is downtime. Of course your architecture must allow for downtime if it happens, but it's lost money either way, your hardware is not doing any useful work while rebooting. So more computers you have, more money is lost. At small scale that's not significant, but at large scale that might become significant so there's more incentive to reduce downtime.

MarkSweep2• 3 years ago

Edit: ignore the below numbers, I got hours and minutes confused.

If you each sever spends 7.5 minutes each month rebooting, that is 1% of all your computers wasted. If you have 10,000 servers, that’s worth 100 severs. If you have 1 million servers, that’s worth 10,000 servers. If each server costs $10,000, that’s $100 million dollars of compute capacity. You can see how that amount of lost computer capacity can start to justify spending engineering time on driving down the amount of time servers are rebooting.

solatic• 3 years ago

You have to design everything for failure. Given that, it shouldn't be hard to take servers out of production for patching and updates.

There's a big, big difference, especially at the scale of hundreds of thousands / millions of servers, between designing such that your architecture can suffer 1% of servers being offline and 10% of servers being offline. If you have 1 million servers, even if you could take 1% of them offline at once (i.e. 10,000 servers), if it takes 5 minutes to reboot, you then need to wait 5 minutes * 100 one-percent-buckets = 500 minutes, or 8.3 hours to do a full patch. When you have critical security updates (like Heartbleed) you simply cannot have unpatched servers exposed to the Internet for that much time. And that's not including the amount of time it takes to actually send reboot/patch commands to 10,000 servers.

The larger the bucket, the more likely a bad patch is noticed by the public, and the more likely that an ordinary traffic spike (for which your extra capacity is ordinarily there for) will overwhelm your servers (since your extra capacity is being used to handle patch rollout and rebooting). Sure, you can plan and add even more capacity to compensate, which makes it take even longer to rollout a patch, and now Finance is knocking at your door wondering if you really need all these servers and maybe you could decommission some of them to save money.

It's a fundamentally difficult problem at hyperscaler scale.

bradknowles3• 3 years ago

If you've seen any of Werner Vogel's talks, you will notice that Amazon and AWS feel the same way. Any scalable service should be able to withstand the loss of some of their components and keep operating.

iseletsk• 3 years ago

There is also KernelCare from tuxcare https://tuxcare.com/enterprise-live-patching-services/kernel... for kernel livepatching. It supports most linux distros.

cloudengineer94• 3 years ago

Been using Kpatch with tons of my VMs, works quite well

1letterunixname• 3 years ago

Roughly 13 million servers at present, with $20B spent on new datacenter gear in 2023 and another $20B in 2024.

Running CentOS 8 Stream currently, going to 9 soonish.

How Meta patches Linux at hyperscale

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