In the past few months I've done 30-40 devOps interviews, and the question of concurrency between services was the single most commonly touched topic when system design questions came up. Companies asked it in various ways, but most of the time the example involved a database and one or more services issuing many simultaneous CRUD requests towards this database. (Usually I answered this question by introducing queues, load balancers, or various redundancy solutions for the database so it can scale.)
When I realized that this was one of the most common questions I started searching online but I haven't found any general and comprehensive articles about this topic. So here I am: how would you generally handle this type of "too many simultaneous requests" problem between two services?