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Re:Kubernetes Failure Stories by tutfbhuf on Thursday February 11, 2021 @03:01PM (#26106353)
The current trend goes to multi-cluster environments, because it's way too easy to destroy a single k8s cluster due to bugs, updates or human mistake. Just like it's not an very unlikely event to kill a single host in the network e.g. due to updates/maintenance.

For instance, we had several outages when upgrading the kubernetes version in our clusters. If you have many small cluster it's much easier and more save to apply cluster wide updates, one cluster at a time.

Re:Kubernetes Failure Stories by colllectorof on Thursday February 11, 2021 @05:55PM (#26108556)
The tech churn cycle is getting more and more insane. It's the same process repeating endlessly.

1. Identify one problem you want to fix and ignore everything else.

2. Make a tool to manage the problem while still ignoring everything else.

3. Hype the tool up and shove it in every niche and domain possible.

4. Observer how "everything else" bites you in the ass.

5. Identify the worst problem from #4, use it to start the whole process again.

Microservices will save us! Oh no, they make things complicated. Well, I will solve that with containers! On no, managing containers is a pain. Container orchestration! Oh no, our clusters fail.

Meanwhile, the complexity of our technology goes up and its reliability in practice goes down. Plus, the concepts we operate with are less and less tethered to reality, which makes even talking about certain issues really hard.

Re:Kubernetes Failure Stories by Karunamon on Thursday February 11, 2021 @06:43PM (#26109067)
I've got a different read on this. It's always been complicated, it's just that each.. I don't want to say "generation", but roughly the same concept, grew up with and internalized and knew about the complexities of the tech stacks they learned, and so when something comes about that moves the abstraction one level higher than what people are used to, it's seen as unstable crap.

This isn't some ageist kids-these-days thing, I mean that the complexity has always existed, and it's always abstracted one level higher over time. Kubernetes doesn't exist because Google and Google-adjacent engineers wanted to foist off "ooh, shiny" on the world, it exists because it solves a problem with containers at scale. Containers solve a problem with resource usage at scale, which are really just an evolution of VMs and a response to their inefficient resource usage and brittleness at scale, and even they were once seen as the new hot fancy overly-complicated thing.

For context, I entered the IT workforce just as virtual machines were being introduced into the average enterprise, and a distressingly high amount of the complaints I hear about containers and k8s were being used against VMs as well.

I'm curious to see where we go from k8s. What the next level of abstraction up will be.

Re:Kubernetes Failure Stories by timeinput on Friday February 12, 2021 @01:27AM (#26111222)
My complaint comes from the at scale part.

I don't do anything at scale. I don't have to scale. My core competency is as a library or tool builder, and often my primary deliverable is a tool or library.

In the past year I got a new JR engineer on my team who was all hot and bothered with docker and k8s and he spent a month changing out CI process to be docker based. It went from a 20 line shell script to a pile of garbage.

I disagreed with the decision at the time, and while a subject matter expert I'm not the team lead so I couldn't say no stop that's bad.

While I'm sure k8s solves problems for Google I'm not google. My company isn't google, and my team isn't solving that class of problems so docker is useless crap for me.

The person is no longer on the team. They left their docker mark, and ran off to dockerify some other project leaving a team with no container expertise and a CI pipeline that is hacks around docker bugs.

Re:Kubernetes Failure Stories by lnenad on Friday February 12, 2021 @08:51AM (#26113601)
Docker on its own is in most cases a great thing with a plethora of benefits. It's worth the upgrade from a 20 line shell script and I feel like you're part of the "I don't like new things gang". On the other hand it should stop there, k8s or swarm or whatever is not necessary for 90% of use cases or applications.
Re:Kubernetes Failure Stories by bacongobbler on Friday February 12, 2021 @02:16AM (#26111377)
Sounds more like a people problem than a tech problem.
Re:Kubernetes Failure Stories by xorcist on Friday February 12, 2021 @03:15AM (#26111651)
Everything is a people problem at the end of the day.
Re:Kubernetes Failure Stories by Karunamon on Saturday February 13, 2021 @12:05PM (#26124781)
This is a thought-terminating cliché.

The existence of right tools for the job implies the existence of wrong tools for the job. The engineer in GP's story used the wrong tool for the job. That is a people problem. Had he used the right tool for the job, the problem would not have existed. GP wrote their CI stuff in shell to solve a tech problem, not a people problem.

Re:Kubernetes Failure Stories by Geezus_42 on Thursday February 11, 2021 @09:29PM (#26110145)
What's that quote about things you grew up with are seen as infrastructure, things invented during your early adulthood are amazing, and everything after is useless crap?
Re:Kubernetes Failure Stories by Lucasoato on Thursday February 11, 2021 @07:24PM (#26109415)
The fact that this is similar to something already happened reassures me a little. May Lambda and other FAAS frameworks be considered the next layer of abstraction? (even if cloud providers are using containers underneath)
Re:Kubernetes Failure Stories by kungfuscious on Thursday February 11, 2021 @08:25PM (#26109810)
Imagine k8s but all the core features you need to run MMO-level apps are the equivalent of simple Unity Engine functions like Instantiate(gameObject). I want. Maybe I help create?
Re:Kubernetes Failure Stories by tharkun__ on Thursday February 11, 2021 @07:47PM (#26109558)
Wow you must be old. Like probably retiring now?

VM/370 came out 49 years ago. So assuming you did a master's at university (I guess math at the time) I'd say you are definite retired by now.

https://en.m.wikipedia.org/wiki/VM_(operating_system)

(yes this is tongue in cheek sort of since you said average but you also said 'enterprise' which my cheek reads as large company :))

Re:Kubernetes Failure Stories by edoceo on Thursday February 11, 2021 @08:19PM (#26109766)
Bruv. You're catching downvotes for two reasons. A: ageism and B: also not realising that tools like the "old ones" used lasted decades. Release dates are a poor metric here.
Re:Kubernetes Failure Stories by tharkun__ on Friday February 12, 2021 @12:46PM (#26116332)
I get it, nobody actually got the joke. Should've put the () first lol.

What I'm playing off of is that the poster probably meant when VMware and such took off in the enterprise. As one would see in my post history I know about what came before and that these things are not new in fact. And in many many cases still in use today which is your second point. What started 49 years ago is still in use on the IBM z series and all of that stuff has awesome backwards compatibility. My dad started his career with 360 assembler (as can also be seen in my post history).

So I guess it's ageism in the direction of _young_ people. I hope it's them down voting. Otherwise it's misjudging peoples sense of humour ;)

Re:Kubernetes Failure Stories by p_l on Thursday February 11, 2021 @08:35PM (#26109853)
to make this comparison funnier...

... the ancient equivalent of Kubernetes was released in 1973 (JES3)

Re:Kubernetes Failure Stories by Gene_Parmesan on Friday February 12, 2021 @03:36AM (#26111742)
I'm with you for most of this, but I do think one element you are missing here is that the ever-increasing scale is at least in part to blame as well. Yes, software is vastly more complicated today, and perhaps suffers more errors, although I would want to see data on that. But, like, YouTube in 2021 is a vastly more difficult engineering challenge than YouTube circa 2008. The same can be said for any site with users numbering now in the millions. E.g., not only have Netflix's streaming user counts exploded since 2007 when it launched, the quality expected now of on-demand streaming has strongly increased as well.

Having said that, in reality that scale applies only to a small minority of products. I think an additional part of the real problem is the ever-present Cargo-Cult Oriented Programming model we've had for a while. I am sure container orchestration is important and maybe even required at places at Google scale. But I hear far too much about its use; it seems that nearly everyone is using it, and I really don't understand why. There seems to be a bit of a keeping-up-with-the-Jones effect, like people would be embarrassed to say that their startup relies on platforms that aren't the latest and greatest. Picking technologies because they sound cool on a resume or at a tech conference, instead of their use being appropriate for the circumstances, seems like a common issue.

Re:Kubernetes Failure Stories by goatinaboat on Friday February 12, 2021 @04:37AM (#26111966)
I really don't understand why. There seems to be a bit of a keeping-up-with-the-Jones effect

The industry strongly incentivises individual engineers to make decisions that will ensure the latest buzzwords appear on their CVs - far more strongly than it incentivises making sound decisions for their current organisation.

Re:Kubernetes Failure Stories by crispyambulance on Friday February 12, 2021 @06:14AM (#26112432)
It's true, nobody wants to be left behind with a bunch of skills that aren't attractive to desirable employers.

There's also very much a tendency to make things complicated in many workplaces as a form of job security and gatekeeping. But it doesn't last forever. Today's hot-shit is tomorrow's ball-and-chain.

10+ years from now, many k8s monsters will still be running and kept alive by stressed-out teams in India. Much like the "Oracle Enterprise Business Suite" giant-shit-ball from the late 90's is still working in many corporations doing absolute critical stuff with tentacles in every part of the org. Changes in these systems are nearly impossible because of the cost and nightmarish complexity, and _everyone_ is _forced_ to use it.

Re:Kubernetes Failure Stories by goatinaboat on Friday February 12, 2021 @07:38AM (#26112985)
There's also very much a tendency to make things complicated in many workplaces as a form of job security and gatekeeping

It’s not only that it’s also boredom. Cranking out another cookie-cutter app can be much more fun if you do it in a novel way. Basically all the incentives are aligned towards exotic over-engineering rather than boring, safe but actually perfectly good choices. The danger will come if any savvy manager figures out what this costs them. So we’re probably all safe but you never know.

Re:Kubernetes Failure Stories by trabant00 on Friday February 12, 2021 @04:09AM (#26111853)
That's exactly what happens. But not out of ignorance and not only in IT. It's recipe for marketing success in any domain. Customers only know the problems of current solutions. Solve those and you get instant influx of customers. Sure, your solution brings it's own problems but it will take a very long time for them to surface and become common knowledge. First people will only check that your solution does fix the old problems in testing environments. And it does, so they move on. When they encounter implementation/production issues that's actually an opportunity for you to sell consulting. People who took the bait early on will mob on any naysayer: "Agile doesn't suck. it's just most implementations, but real Agile rocks!"
Re:Kubernetes Failure Stories by thinkharderdev on Friday February 12, 2021 @07:09AM (#26112790)
I think about it differently. The "problem" is that we are solving problems that didn't need to be solved before (or so we thought). The infrastructure I work on today is in many ways much more complex but it also handles a lot of things that we just didn't back in the day when everything was simpler.
Re:Kubernetes Failure Stories by AmericanChopper on Thursday February 11, 2021 @11:24PM (#26110721)
> Meanwhile, the complexity of our technology goes up and its reliability in practice goes down.

I don’t agree with this at all. Reliability in practice is improving at a phenomenal pace. 10 years ago maintenance outages were a normal feature of every service, and unplanned outages were perfectly ordinary occurrences. Consumers today expect a much higher level of availability and reliability, which they receive rather consistently. Today it takes much less resource to produce a much more reliable system then you would have been able to produce in the rather recent past.

Re:Kubernetes Failure Stories by fogetti on Friday February 12, 2021 @12:45AM (#26111066)
I don't know which industry you worked in, but outages in the telecom industry was strictly forbidden and came with severe financial penalties even 10 years ago. And those companies managed to adhere to really strict uptime SLAs even then.

It might take less resource today though to achieve the same, I agree with that.

Re:Kubernetes Failure Stories by AmericanChopper on Friday February 12, 2021 @01:02AM (#26111136)
Telcos have historically had availability regulations in many places because of how people rely on them for access to emergency services. So they’re a special case here, and the amount of resources they invested into optimizing for that is beyond the capacity for most organizations.

10 years ago I was working for a company that provided a financial OLTP service. We had to invest a huge amount of money to be able to provide a reasonable HA architecture, and to be able to meet 4 hour DR SLAs, and we still had weekly maintenance outages. The amount of effort required to accomplish those service levels today is comparatively trivial, and you could reasonably expect even a low-budget one person operation to be able to exceed them.

You’d expect a service outage to be a significant public controversy today for a lot of companies. It’s never been a good thing, but we’ve come a long way from it being a completely routine event for most services. Especially given the explosion in online services.

Re:Kubernetes Failure Stories by Lutzb on Friday February 12, 2021 @02:44AM (#26111494)
Depends on what you compare. If you compare mainframes vs k8s I would say reliability is not on par yet. If you compare commodity systems with simple monolithic apps vs k8s system maybe we just reached parity.
Re:Kubernetes Failure Stories by superbcarrot on Thursday February 11, 2021 @03:42PM (#26106847)
Sounds like madness. Should we expect a new tool that orchestrates all of your Kubernetes clusters?
Re:Kubernetes Failure Stories by yongjik on Thursday February 11, 2021 @04:42PM (#26107714)
> There are two ways of constructing a software design: One way is to make it so simple that there are obviously no deficiencies, and the other way is to make it so complicated that there are no obvious deficiencies. The first method is far more difficult.

- C. A. R. Hoare

Re:Kubernetes Failure Stories by ex_amazon_sde on Thursday February 11, 2021 @06:26PM (#26108915)
Ex Amazon SDE here. I would pick the first method a hundred times.

People would be surprised at how simple the internal infra is, given the fleet size, compared to stuff like k8s.

(I'm talking about the infra that runs on bare metal, not AWS)

Re:Kubernetes Failure Stories by fremanator on Thursday February 11, 2021 @09:41PM (#26110190)
Amazon SDE here. I'm not sure what internal infra you're talking about. Amazon's certainly isn't one of them.

And AWS, with its design by accretion, makes that an impossibility. Kubernetes by comparison is a paragon of clarity.

Re:Kubernetes Failure Stories by emptysongglass on Friday February 12, 2021 @01:41AM (#26111264)
Why does AWS insist on building this way? Has anyone tried to get the teams together and say, "stop, let's evaluate and simplify where we can?"

As an AWS customer, I find AWS a huge pile of overcomplicated offerings that is dense with its own jargon and way of doing things. IAM is a trash fire. Everything built on IAM like IRSA is also a trash fire. Why are there managed worker nodes, spot managed worker nodes, Fargate worker nodes, self-managed worker nodes, and spot self-managed worker nodes? Why are there circular dependencies for every piece of infra I stand up making it almost impossible to delete any resources? Why can't I click on a service and see how much it costs me in one or two clicks?

This is a completely insane way of building software to me and I have to eat it.

Re:Kubernetes Failure Stories by ex_amazon_sde on Friday February 12, 2021 @12:43PM (#26116287)
> "let's evaluate and simplify where we can?"

Amazon has "Invent and Simplify" as one of the leadership principles. However, each team has its own hiring bar and culture, so some will take it seriously and some will not.

> I find AWS a huge pile of overcomplicated offerings

I fully agree. I'm speaking exclusively about the internal infrastructure, not about AWS.

Re:Kubernetes Failure Stories by ahoka on Friday February 12, 2021 @05:37AM (#26112227)
As if they are trying to tie them to their proprietary platform to make migration to other cloud providers hard.
Re:Kubernetes Failure Stories by bfrog on Thursday February 11, 2021 @10:06PM (#26110341)
I can't even imagine, sometimes I feel like AWS offers this pretty facade of "scale it up easy" and in reality its like "wait, I can't even see why this thing is failing because its a layer below, and AWS support costs mega bucks"
Re:Kubernetes Failure Stories by paulryanrogers on Thursday February 11, 2021 @09:31PM (#26110153)
You mean the infra behind non-AWS services like retail Amazon.com?

Or the infra underlying AWS itself?

Re:Kubernetes Failure Stories by ex_amazon_sde on Friday February 12, 2021 @12:05PM (#26115791)
The first one, but I'm trying not to divulge too many details on the architecture of Amazon - as you can imagine.
Re:Kubernetes Failure Stories by paulryanrogers on Friday February 12, 2021 @11:15PM (#26121350)
Fascinating because I would have thought the whole idea is AWS is dog-fooded by retail. Yet in truth AWS is itself too expensive and / or complex for Amazon itself! (Or at least the original part of it.)
Re:Kubernetes Failure Stories by ex_amazon_sde on Friday February 19, 2021 @04:36PM (#26198322)
The majority of retail is dog-fooding AWS, but a lot of code was written before AWS existed or before it provided many of the required services.
Re:Kubernetes Failure Stories by bo0tzz on Thursday February 11, 2021 @03:57PM (#26107052)
Re:Kubernetes Failure Stories by seneca on Thursday February 11, 2021 @07:48PM (#26109568)
CAPI is for creating clusters only. It doesn't offer any orchestration.
Re:Kubernetes Failure Stories by moondev on Thursday February 11, 2021 @11:57PM (#26110883)
I'm curious what you mean here, since CAPI allows you to manage and scale clusters like any other Kubernetes object. You can literally "kubectl scale --replicas" a cluster control-plane and worker nodes.
Re:Kubernetes Failure Stories by YawningAngel on Thursday February 11, 2021 @04:18PM (#26107358)
You end up needing this anyway, because Kubernetes clusters are confined to single geographic regions and you need some way of managing the separate cluster(s) you have in each region
Re:Kubernetes Failure Stories by WJW on Thursday February 11, 2021 @05:07PM (#26108038)
Not saying you should, but it's entirely possible to have nodes all over the world managed by a single set of master nodes. The system is not really designed with that use case in mind though, the added latencies will hurt a lot in getting etcd consensus.
Re:Kubernetes Failure Stories by tutfbhuf on Friday February 12, 2021 @04:20AM (#26111898)
While it is certainly possible to have mixed region clusters, from my experience it is better to have one cluster per region. Do your synchronous communication within the cluster / within the datacenter with sub millisecond latencies and do asynchronous communication across cluster boundaries with up to triple digit millisecond latencies.
Re:Kubernetes Failure Stories by bcrosby95 on Thursday February 11, 2021 @03:59PM (#26107068)
A Kubernetes for Kubernetes! But what about when we want to upgrade that?
Re:Kubernetes Failure Stories by dabeeeenster on Thursday February 11, 2021 @04:28PM (#26107519)
I mean thats simply Kubernetes for Kubernetes for Kubernetes. Lets go!
Re:Kubernetes Failure Stories by testplzignore on Thursday February 11, 2021 @04:38PM (#26107662)
I need a Kubernetes Kubernetes Kubernetes Kubernetes Kubernetes emulator so I can run Civilization 14 on my iPhone 35XSXS.
Re:Kubernetes Failure Stories by higeorge13 on Thursday February 11, 2021 @04:57PM (#26107923)
Inception!
Re:Kubernetes Failure Stories by verst on Thursday February 11, 2021 @11:27PM (#26110734)
In a way this reminds me of Kubernetes Virtual Clusters. Each virtual cluster has its own tenant control plane, namespaces. Multiple virtual clusters exist in a super cluster.

https://github.com/kubernetes-sigs/multi-tenancy/tree/master...

Re:Kubernetes Failure Stories by tutfbhuf on Friday February 12, 2021 @04:31AM (#26111940)
I think at a certain point up in the stack you don't want to have another orchestrator for the orchestrator. You would just tell each team to keep their cluster up-to-date without creating a (dangerous) master button to update them all at once.
Re:Kubernetes Failure Stories by rwoerz on Friday February 12, 2021 @10:15AM (#26114496)
Wake me up when I can finally run a bare-metal Kubernetes cluster in Kubernetes to get rid of all my hardware.
Re:Kubernetes Failure Stories by durnygbur on Friday February 12, 2021 @06:16AM (#26112440)
To ugrade it you summon Scrum of Scrums, the Master Scrum Master has all the answers you might need.
Re:Kubernetes Failure Stories by jachee on Friday February 12, 2021 @01:19AM (#26111190)
Isn't that basically what helmfile[0] does?

It lets you declaratively define helm deployments, which in turn orchestrate k8s infrastructure.

0 - https://github.com/roboll/helmfile

Re:Kubernetes Failure Stories by 6nf on Friday February 12, 2021 @01:07AM (#26111151)
Agreed, this is absolute insanity and people can't see it from the weeds.
Re:Kubernetes Failure Stories by Aeolun on Thursday February 11, 2021 @06:42PM (#26109055)
I think we’re already there? Maybe we’re better off looking for a cluster orchestrator orchestrator.
Re:Kubernetes Failure Stories by thirdlamp on Thursday February 11, 2021 @04:07PM (#26107192)
it's kubernetes all the way down
Re:Kubernetes Failure Stories by seneca on Thursday February 11, 2021 @07:50PM (#26109582)
That's what Federation in Kubernetes was for, sort of, but it has never really come to fruition. The closest I've seen is Admiralty, but I'm not sure how it actually works out in reality.
Re:Kubernetes Failure Stories by p_l on Thursday February 11, 2021 @08:37PM (#26109863)
Federation v2 is nice, but not many places use it.

Unfortunately, all my clusters are either confined locally anyway, or are deliberately supposed to be separated in all ways :(

Re:Kubernetes Failure Stories by codeulike on Thursday February 11, 2021 @04:07PM (#26107196)
Kubermeta
Re:Kubernetes Failure Stories by theptip on Thursday February 11, 2021 @04:40PM (#26107685)
It used to be called Ubernetes, shame that name didn't stick.
Re:Kubernetes Failure Stories by jknoepfler on Thursday February 11, 2021 @04:40PM (#26107689)
I operate one at work, actually. It's not so bad.
Re:Kubernetes Failure Stories by nyellin on Friday February 12, 2021 @01:54AM (#26111304)
Kubernetes solves a problem. It isn't appropriate for all use cases, but the real problem isn't kubernetes but rather the knowledge gap around new technology.
Re:Kubernetes Failure Stories by verdverm on Thursday February 11, 2021 @04:29PM (#26107527)
Re:Kubernetes Failure Stories by mullingitover on Thursday February 11, 2021 @04:10PM (#26107236)
Rancher does this nicely.
Re:Kubernetes Failure Stories by xiwenc on Friday February 12, 2021 @02:28AM (#26111421)
Are you implying we need a manager1 (k8s) to manage containers? This manager1 cannot be trusted so introduce manager2 to manage manager1? What’s next? We need to look forward to manager3?

I dont like where this is going

Re:Kubernetes Failure Stories by avereveard on Thursday February 11, 2021 @06:13PM (#26108802)
What are the best practices for transactional data storage in multi cluster environments, just ditch databases and go for distributed, raft based, nosql variants?
Re:Kubernetes Failure Stories by trever123 on Friday February 12, 2021 @06:40PM (#26119901)
CockroachDB works very well for this
Re:Kubernetes Failure Stories by pojzon on Thursday February 11, 2021 @09:21PM (#26110109)
Thats a very good question Im also interested in knowing the answer. Currently I have seen that every company I had a pleasure to work with had to settle with „eventual” consistency of replicated masters. This is ofcourse totally unacceptable in case of some industries. Thats why I would like to know whether someone found a holy grail of multi-region database design and is willing to share it for free!
Re:Kubernetes Failure Stories by tutfbhuf on Friday February 12, 2021 @08:08AM (#26113204)
Eventual consistency happens when you allow your write transaction to finish, before the data has been spread across all masters. It allows you to have fast writes, but it's actually cheating (in my opinion), because only one master (the nearest) has seen your write, while the others don't know about it yet.

If you want to have a strong consistent multi-region database (or other form of storage), then you have to deal with slow writes, because your transaction is only allowed to terminate successfully when all masters have written the new data and are in a synchronous state.

I very much prefer slow strong consistent writes instead of fast eventual consistent writes.

Re:Kubernetes Failure Stories by h43k3r on Friday February 12, 2021 @09:47PM (#26120952)
Lookup Google's Spanner. It's a distributed transactional SQL database with whatever consistency levels you are interested in

Disclaimer- Google employee who is heavily using Spanner

Re:Kubernetes Failure Stories by tutfbhuf on Saturday February 13, 2021 @04:11AM (#26122431)
Yes, but Google Spanner is not open source, so it's not so easy to actually look at it. But what is known to public is that Spanner relies on perfectly synchronized atomic clocks within their datacenters, called TrueTime. This solution is very special and does not work for other databases in general.
Re:Kubernetes Failure Stories by waynesonfire on Friday February 12, 2021 @06:23AM (#26112482)
Am i not understanding the assumptions in your question or is it underspecified?

But, whats wrong with postgres here?

Re:Kubernetes Failure Stories by flurdy on Friday February 12, 2021 @12:36PM (#26116204)
Which is why GCP's decision last year [1] to encourage people to only use 1 cluster with GKE for all of your minor, internal, exploring, testing, side and hobby projects was so frustrating.

For your main production load at work, paying management fees for many clusters is not that relevant costs. So not an issue with my clients' projects.

But for my many hobby-projects, dev and few self-employed business workloads balancing them all on as few clusters as possible is a major pain.

Before that I/you scaled it out to separation of concerns, maybe only grouping a few workloads. And then quite happily scrapping whole clusters all the time.

Now any lifecycle issues with them affects lots of independent applications. They went from cattle to pets over night.

[1] https://www.reddit.com/r/kubernetes/comments/fdgblk/google_g...

Re:Kubernetes Failure Stories by hinkley on Thursday February 11, 2021 @07:00PM (#26109222)
There's a fun one I hadn't thought about that was mentioned here sometime last summer:

What do you do if your Raft data is in zookeeper and you want to move it to etcd or consul? We need 'migrations' for our non-db data too.