[mrweasel]

5000 stores, let's say 10 checkout lines per store, just to overprovision, so at worst 50000 simultaneous transactions going on, but probably way less. You can do that with a single server, but you'd want some redundancy and spare capacity.

I worked with a Danish retailer with +3000 store in ~50 countries, and even adding their webshop on top and they were closer to 200 (maybe 300) servers (most VMs). Then you need the ActiveDirectory, office IT, all that stuff, with redundancy and it adds up quickly... but not to 40K.

What I will say that people forget is that production might be 8 beefy VMs, you still need to replicate that to a number of test systems, staging environments and so on. So a 8 node production cluster because maybe 24 servers when accounting those other environments.

[venzaspa]

I'd assume most of the big supermarkets have a 4-5 host cluster with the small local stores having a 2-3 host cluster. You've got the software to run the tills sure, but also the loyalty card system (which seems to have a local cache at each site based on how quickly it returns your first name), VoIP, Door Access systems, BMS, Digital Signage, Scan as you shop systems, CCTV, Stock management systems..

I can see how you hit 40k pretty quickly.

[whatever1]

See these numbers I buy. 40k smells over engineering to me (or more likely a 3P salesman made a huge bonus after selling the architecture to tesco)