Cell-based architecture for resilient payment systems

Whole lot of nothing.

This isn't about payment technologies, it's not about isolating transactions, it's about scaling the middle layer. What's worse it's not even explained what middle layer does.

No info on how routing works, no info on data synchronization.

Folks just learning Kubernetes and write extremely abstract stuff.

Nobody uses Amex for payments, so the system isn't ever under high load.

Just kidding!

I find the idea quite good, and have to assume that the amount of payment fails they experience due to partitions/outages isn't very high and that the post-payment reconciliation and reclamation process gives them the liberty to rank availability a bit higher than correctness.

One thing that looked a bit shaky was the interplay between the global transaction router's state of knowing which cells can handle a particular payment and the asynchronous distribution of the "failover data", which I presume it needs to know to route correctly. To me that seems to create a window where it might route to the wrong cell due to an outdated routing state.

It also doesn't go into the HA setup of the global transaction router itself.

But still, I kind of like the design.

Some of it sounds like it reinvented Erlang supervision trees https://learnyousomeerlang.com/supervisors. As a joke there we’re calling gen_severs “nanoservices”. Granted, that was mostly when microservices were the hot new thing.

microservices / clusters / zones - really all of these are other "cell-based" architectures as well. there is absolutely no written rule that a microservice was just an API or a singular service, it basically can be a independent instance that is testable/usable/gives value on itself.

that said: still a nice write up, learning about some of the architectural choices that AMEX makes is definitely insightful (and relavent/useful to what i am working on right now as well!)

All i can see is a giant single point of failure called the Global Transaction Router.

yo, 2022 called and they want their buzzwords back:

https://news.ycombinator.com/item?id=32023863

https://wso2.com/engineering-platform/developer-platform/doc...

As described, if one "cell" crashes, you re-route/retry everything on the other cell. Assuming your system is deterministic and the inputs stay the same, the second cell should now break as well.

This reads to me like an attempt to patch a system that's already fucked beyond belief while pretending you're doing "engineering".

Fancy implementation of a retry loop attempting to minimize downtime.

403 Forbidden

Because of the title I was expecting to read about doing payments with a distributed network, like a terrorist cell network, or something like Hawala. Not (as I infer from other comments) Amex using multiple independent systems.

Blockchain payments lite

"We broke our monolith into microservices and wish we hadn't"

I wonder how they ensure durability. Is it possible that a cell going down would roll back a payment after it has occurred. Or do they depend on a non cell database?

There things are always a clusterfsck compared to the mainframe deployments.

Backing up would be hell

As Reddit already pointed out, this is nothing novel.

Ah yes, the financial services company that runs a travel agency, allows me to book my hotel and rental car weeks in advance, registers a hold for incidentals for both the hotel and car when I check in, then blocks the card when I try to buy dinner that night in that same hotel due to fraud detection.

Last week it required me to take pictures of my face from multiple angles to regain membership privileges. I suspect this may be part Palantir data collection and part Peter Thiel dating service.

This service oriented architecture except more expensive and complicated.

American Express tech is some of the worst in the world among big companies. All of the value in the company is just in the branding. They put some work into the mobile app and the website, but other than that, its a facade.

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Makes me a little nervous that a web page about resilience is failing to connect.

They run their payment systems on ps3??? Somebody bought into the marketting a bit much.

So you’re telling me these cells operate independently like distributed Ethereum nodes and L2s… got it.