Post

Common Misconceptions about AWS Lambda 1. The Lambda function cold start is free. Soon, Not anymore. Effective August 1, 2025, cold start will be charged (surprised it took this long)

2. The Lambda function scaling is infinite. No. Check your account limits. If you open a new account, you will get 10 concurrent executions by default. You need to request more concurrent executions.

3. The Lambda function scaling is instant. No. Lambda has a limit on how fast your functions can scale. Your instant execution environment instance is 1000.

And in every 10 seconds, Lambda will scale up to another 1000 instances. Note that the first instant 1000 instances are more than enough for most use cases.

Be cautious with memory usage. For example, most of the time, 512 MB is preferable to 256 MB or 128 MB, which results in more CPU credits, faster execution, and potentially lower costs. Increasing memory alone will not always be the most cost-effective solution.