From an EU perspective, most interbank communication for SEPA is through XML following PACS or CAMT xsd’s (so there’s a PACS format to transfer money, a CAMT format to inquire on the status of a payment etc.) sent via an intermediary clearing house. Used to be huge XML batches, but now moving to small XML messages.
Internationally also “MT” messages are used, which is also a file with specified format.
So it doesn’t really matter what stack you run, as long as it can create files and send them out :-)
I can't verify 100%, but I think Orange Bank (subsidiary of the telco provider) is entirely built on the cloud. I believe they built all their systems ground-up 2 years ago, but I could be wrong. When they acquired Groupama Banque, I think they basically started over on the systems.
