There are a few reasons, it gets complex, but it isn't just invocation, it is billed by a combination of invocation and time. https://aws.amazon.com/lambda/pri

There are a few reasons, it gets complex, but it isn't just invocation, it is billed by a combination of invocation and time. https://aws.amazon.com/lambda/pricing/ https://aws.amazon.com/lambda/pricing/ That time includes the amount of time to spin-up the lambda. Ours is a long-running lambda, and we benefit from some local cache when they are running as well. In order to handle the load, we had to extend the number of lambda's available on our account as well, so we are talking about 1000s of seconds being eaten up every second.