It's every time you have to start up a lambda instance. So if you're low, continuous traffic, it'll happen once and you won't really care. If you're high traff

It's every time you have to start up a lambda instance. So if you're low, continuous traffic, it'll happen once and you won't really care. If you're high traffic, occasionally different instances will get started up, will also need their node network interface, and also take 6+ seconds. And if you're low traffic but not continuous, if there's a pause for more than around 15 minutes (entirely depends on how much demand there is for lambda and how rapidly they clean up old containers), for the next request you get you'll have to cold start again.