Runtime API allows you to write your Lambda functions in any language, provided that you bundle it with your application artifact or as a Lambda layer that your application uses.
As an example of using this API and based on the customer demand, AWS is releasing a reference implementation of a C++ runtime for Lambda. This C++ runtime brings the simplicity and expressiveness of interpreted languages while maintaining the superiority of C++ performance and low memory footprint.
When building serverless applications, it is quite common to have code that is shared across Lambda functions. It can be your custom code, that is used by more than one function, or a standard library, that you add to simplify the implementation of your business logic.
Previously, you would have to package and deploy this shared code together with all the functions using it. Now, you can put common components in a ZIP file and upload it as a Lambda Layer. Your function code doesn’t need to be changed and can reference the libraries in the layer as it would normally do.
A function can use up to 5 layers at a time. The total unzipped size of the function and all layers can't exceed the unzipped deployment package size limit of 250 MB.