So much has been written about Lambda cold starts. It’s easily one of the most talked-about and yet, misunderstood topics when it comes to Lambda. Depending on who you talk to, you will likely get different advice on how best to reduce cold starts. So in this post, I will share with you everything I have learned about cold starts in the last few years and back it up with some data.

When you build your application on top of Lambda, AWS automatically scales the number of “workers” (think containers) running your code based on traffic. And by default, your functions are deployed to three Availability Zones (AZs). This gives you a lot of scalability and redundancy out of the box. When it comes to API functions, every user request is processed by a separate worker. So the API-level concurrency is now handled by the platform.