Spring Boot 2 applications can be slow to start, particularly if they discover and initialize a lot of components. In the example above, we recommend using a static block or the constructor of your RequestStreamHandler class to initialize the framework to take advantage of the higher CPU available in AWS Lambda during the initialization phase. However, AWS Lambda limits the initialization phase to 10 seconds. If you application takes longer than 10 seconds to start, AWS Lambda will assume the sandbox is dead and attempt to start a new one. To make the most of the 10 seconds available in the initialization, and still return control back to the Lambda runtime in a timely fashion, we support asynchronous initialization:

https://github.com/awslabs/aws-serverless-java-container/wiki/Quick-start---Spring-Boot2