How we prepared Monzo's systems for a £20 million crowdfunding round

On a normal day (in 2018) Monzo usually sees around 150 requests per second to an individual API, and 1,500 requests per second to our system as a whole. But when we opened an investment round to new investors at 10am on Wednesday 5th December, we immediately started receiving 1,800 requests (calls for information or attempts to perform an action) per second to our investment APIs (application programming interfaces). Our system as a whole was receiving 4,300 requests per second.

See the post linked below on the Monzo blog which discusses some of the steps we took to prepare for such a sudden and large amount of API traffic.