Learn the technical side of how Monzo replaced a critical live system without anyone noticing by viewing Irina’s talk here. 👍 For news and articles from Skills Matter, subscribe to our newsletter here.
How Monzo is shaping banking today
Monzo has emerged to give a new perspective on how banking works. Starting as a prepaid service, the company is now a full-fledged bank but does not have any physical branches. This is nothing new and Monzo and its competitors share the same challenges: growing from a small start-up means that services and platforms need to be revised for changing needs.
Irina Bednova, Senior Software Engineer at Monzo spoke at muCon London this year. With her team, Irina looked at payment processors used by the large user base to transfer millions of pounds to see how they could be improved. In a talk she delivered entitled How Monzo Replaced a Critical Live System Without Anyone Noticing, Irina explored her experiences in rebuilding services to be robust and extendable.
To know how to improve a process, you first need to know the process.
In Monzo’s case, this meant breaking down what is needed for money to actually move.
Irina Bednova: “You can start with a very simple solution. Monzo can set up a relationship with Barclays and say, ‘Hey, when our customers want to send money to your customers let’s somehow move money between each other’.
“So, how it’s done is through correspondent banking. There are two banks on either side. These banks have accounts with each other. These are not customer accounts. Monzo has an account in Barclays and Barclays has an account in Monzo. Every time customers want to send money to each other, the bank sorts it from their accounts.
“In fact, this is how a lot of international payments actually work, but if we want our customers to send money to people from all UK banks, we need the corresponding relationship with all the banks, which is difficult.”
Identify the point of the mechanism
What does it do and what are the external elements that you need to meet when rebuilding your service?
Irina Bednova: “Faster Payment Scheme (FPS) is an organisation that handles this (payment processing) for banks. So instead of going directly and opening a Monzo account at Barclays, we become participants of the FPS. On a more technical level, FPS creates an infrastructure where banks send messages to each other via the protocol defined by the FPS.
“How the banks are technically connected is not as important. The point is that messages are being exchanged between the banks via the scheme.
“The very simplistic happy path is customer A wants to send money to customer B, FPS approves this to the recipient bank and the recipient bank approves with the response message.
“FPS has existed for at least a decade or two and is implemented by the majority of banks. There is a lot of documentation. They are not a startup, their integrations and API are not completely straightforward. We had to figure out what the protocol actually is and how to implement it.”
You’ve built the service and are confident to roll it out. Should you?
Irina Bednova: “(The end result) seems very obvious but sometimes it is difficult to figure out a way to roll out a feature or refactor. For us, it was difficult because, due to some idiosyncrasies of the scheme, it was difficult to write the code and decide where the message should go. Should it go to the new processor or the old one because it’s missing parameters?
“At this stage, it becomes very tempting to say, ‘We tested inside and out, we know exactly what is going on. I’ve read nothing but Faster Payments documentation for the last year. Can we just roll it out at 3am when everyone goes to sleep and if something goes wrong, roll it back?’ No.
“We needed to fight this urge to cut corners and actually figure out the way to roll it out gradually, which we did.”
Learn the technical side of how Monzo replaced a critical live system without anyone noticing by viewing Irina’s talk here.
