You can implement any service you want fully on serverless unless you need to use Websocket (then you'd need to combine serverless API with a traditional server). To avoid race conditions you can look into transaction locking (ex: in Postgres): stackoverflow.com/questions/4… or you can set flags with a Redis caching layer. The reason why you should always close your DB connections is that functions create a new connection on each invocation. Considering that it's infinitely scalable, we get a bottleneck at the DB level. So your database solution should be ready to handle thousands of connections at the same time.