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- Hacker News
- By using another US hyperscaler for your backup platform you're still unhedged against US governance failure/breakdown.by guiriduro
- Surely by being a bank, you are already exposed to that.by lmz
- You have no choice really if you’re a UK business, there is no UK (or French, or German, or Japanese for that matter) cloud that can do what AWS or GCP doesby ifwinterco
- An increasing risk for sure.by sdcfgy
- I think this is what distributed systems has a phrase for: "graceful degradation".by tarun_anand
- [2025]by ascorbic
- Almost seems like they can do anything at monzo.comby Valodim
- The only limit is themselves.by stavros
- Monzo is great. Rare example of a consumer banking company that makes things easy. I just signed up for their phone service in literally 3 minutes. Didn't even need to talk to anyone to port my old number. I'm going to move all my ISAs and SIPP to them next I think.by IshKebab
- This is either a bot comment, or you have a very poor understanding of the UK financial market. They are quite far down the leaderboard for ISA rates and SIPPs.by broadben12
- Same service with HSBC and Giffgaff here. Meh.by sdcfgy
- they don't offer a phone contract..? this makes no sense
- Compared to Lebara or other cheap MVNOs their offering is not great. While they eventually give you 30% off (after 6 years) their starting price is 30% higher.by rjh29
- > Didn't even need to talk to anyone to port my old number
That seems like pretty low stakes – I wouldn't expect to talk to anyone to sign up and transfer to a consumer service in the UK. I don't think I've spoken to anyone for something like this in the last 10 years or so.
by danpalmer - Something like this has been top-of-mind for us since we have a heavy reliance on AWS, which was made evident with the VPC Origin failure earlier this year.
Multi-cloud is best cloud.
by qmarchi - Just pointing out this is from February 2025, so has been a thing for a whileby jmkni
- > Monzo Stand-in is an independent set of systems that run on Google Cloud Platform (GCP)
Given the US Cloud Act, how Monzo is protecting customers' financial data from being accessed by foreign government without Monzo's knowledge?
Everyone does it, does not excuse it.
Also shows lack of faith in British business.
by varispeed - Which British businesses provide this sort of infrastructure?
I ask this as a Brit who ran stuff on a few UK providers, and ultimately moved to a cloud platform because of the combination of terrible service and lack of features. The landscape may have changed, but in my experience it was bleak circa 2020.
by danpalmer - There are 3 things I have in mind when reading this:
- it should be so frustrating for a dev to work on a full core banking that is mostly useless and userless except maybe 1h every 3 years.
- if you build a totally different implementation to handle high traffic transaction from third parties that don't operate for days or months, i would expect it to be fragile. Like for example suddenly you receive unicode special chars that you didn't expect in labels and boom.
- last, I think that in most incident cases, the situation is not clear enough to be able to switch to the full different system. Rarely it will be your whole infra but part of it, so there is always the question to what to do in such a case, or if your main infra goes crazy with loops for example, or if you lose control because of a network, aws, infrastructure issue thr problem might be that you have no visibility on what is working and what is not, not necessarily the control to stop the faulty services, etc...
by greatgib - "it should be so frustrating for a dev to work on a full core banking that is mostly useless and userless except maybe 1h every 3 years."
When other banks go down and Monzo stays up, even for 1 hour, that is a massive PR win and will bring in new customers. It's also been used multiple times as of the article (2025), and they are always exposing some users to it for testing.
by rjh29 - Minor thing but I do like they use the word "Stand In" here in the payments / financial sense of Stand-in processing (STIP), which is usually used when a bank is offline to keep essential services such as public transport working.by janpeuker
- Due to the recent outage where it didn’t work properly, this should be renamed Monzo Limp-In.by sdcfgy
- Monzo I've Fallen And I Can't Get Upby lozenge
- Simple Bank, when they were a thing, published this "look at how awesome we are" post about moving to Riak from Cassandra. (I think that's what it was; it's been a long time.)
"We're going to be so reliable after this; big banks don't stand a chance" was what I took away from it.
The migration went horribly. Tier 0 clusterfuck. Debit cards were completely unusable and they lost ledger data. That and the occasional duplicate transaction (like the duplicated student loan payment that put me in a really bad spot at the time, which I was only given $50 for the inconvenience) was enough for me to _run_ bank to Chase.
So, yeah, I get why the big banks are totally fine with keeping their mostly-rock-solid core banking functions on the mainframe and stick with datacenters everywhere.
by nunez - I can't help but think this isn't the best idea, it raises so many questions. How does fail over work (it failed for me!), can you safely fail over, how does product think about the stack, is it funded well enough, how do you scale a system from zero to all traffic instantly, how do you effectively keep this environment warm, how do you determine which services are critical enough to be in it, how do you manage finding the bugs in two separate stacks, and so on and on and on.
It seems like it would be better to invest in a platform that is distributed across multiple failure domains. Some companies call this a cell architecture. For Monzo this might mean true multi cloud, but they already have bare metal services for bank integrations so they are already hybrid in some respects.
It's not the decision I would have made, and I'm not sure I agree with their reasoning, but I'll also admit that I have not run a bank, I don't know all their constraints, and there are some good tech folks at Monzo. That said, I am an SRE at Google so I'd like to think I'm not completely naïve here.
Edit: after reading in more detail I'm puzzled. The justification for Stand-In and not traditional scale-out is the difficulty of data consistency (agreed!), but then Stand-In is just eventually consistent anyway, and introduces sync problems in both directions. Admittedly I'm spoilt by Spanner, but I do wonder if Monzo is being bitten by past architecture choices here.
by danpalmer - So I've been spending a lot of time in the financial services/payment space and might be able to answer some of your questions.
The EU activated the Digital Online Resiliency Act (DORA) last year (passed in 2023) which, amongst other things, mandates that financial services providers who run their core business functions in the cloud (i.e. Monzo) must be able to demonstrate that they are not entirely reliant on a single cloud provider. Otherwise, big, big fines.
Like GDPR, there are auditors that are responsible for signing off on EU DORA compliance. Also like GDPR, there are ways to check those boxes without _really_ checking them. This is probably why Stand-In only has 18 services in its GCP failover "region" instead of the 1K+ production services in AWS; it's just enough to keep critical services (payments/card networks, balances, ledger, etc.) operational and, more importantly, keep DORA auditors at bay.
This article IMO is more for other FSIs who _want_ to run _entirely_ in the cloud (there are very, very few that do). Financial services is a very risk-averse industry. Most providers have biz-critical systems running on mainframes still. (Mainframes are practically indestructible and are much more technically-interesting than people give them credit for, but that's another post.) Being able to tell AWS "yeahhhhh we can run this business on GCP and/or Azure in literally 10 minutes" is a money line for procurement to use during price negotiations. Or at least it was until RAM prices mooned hard enough to make their existing datacenter inventory suddenly very attractive.
Cloud-aside, pretty much every bank in the US has some architecture like this for their critical banking systems, except they are usually an old-school hot-cold (sometimes hot-hot) datacenter failover strategy. Historically failover has been done manually with a runbook (with some automation) and tested during DR/BCP days (sometimes more frequently). They, of course, have zonal/regional replication in place.
by nunez - I think the biggest problem is the data consistency. Since they are planning for eventual consistency, should make it easier, but they most probably had to re-write code to support atomic operations and proper transaction isolations.
But the scaling problem is still there, when they switched over I assume they would start both horizontal and vertical scale of k8 pods and maybe even bump up DB instances as well which could result in a small congestion at the start of the switch over
- I suspect Monzo was bitten by complexity. The network should not be assumed to be reliable and if you make a thousand things (microservices) with network between them regardless of what you think may happen, it’s entirely impossible to test it with any level of certainty. And that’s worse if you have a complete failover scenario.
Add the instability of the average cloud control plane during an outage and things get rather nasty rather quickly in reality. We’ve been through that with AWS’ numerous outages.
My company is victim of this mindset. We sacrificed tested and assured reliability on physical hardware in multiple redundant data centres for cloud and microservices. Mostly driven by Monzo’s claims, semi religious thinking and me too.
Reliability is measurably down, cost is higher, latency is higher and we cannot fail over to another provider because someone went to an AWS conference and started using all the toys. Even if we did get rid of those dependencies, during an outage the kubernetes control plane is so tied into the vendor that we’d be fucked anyway. Last time the ingress controller couldn’t change ALBs for example.
Only winner here is Bezos and the decision makers CVs. The losers are the customers. We live in the stupidest of times.
by sdcfgy - No, it's a great idea. Any systems engineer knows redundancy is good, even better if it's across providers. I see no issues with this from a system architecture point of view. As to how the implementation is done that's up to them to do right.by ricardobayes
- monzo r the same guys who went in on micro services. at a time they were bragging 3 micro services per engineer. so yeah a lot of things don't make sense.by dzonga