Serverless developers frequently import libraries and dependencies into their AWS Lambda functions. While you can zip these dependencies as part of the build and deployment process, in many cases it’s easier to use layers instead. You can configure your Lambda function to pull in additional code and content in the form of layers. A layer is a .zip file archive that contains libraries, a custom runtime, or other dependencies. With layers, you can use libraries in your function without needing to include them in your deployment package. Layers let you keep your deployment package small, which makes development easier. You can avoid errors that can occur when you install and package dependencies with your function code. You can create layers, or use layers that AWS or an AWS customer has published. Layers support resource-based policies for granting layer usage permissions to specific AWS accounts, AWS Organizations, or all accounts.
Layers are extracted to the /opt directory in the function execution environment. Each runtime looks for libraries in a different location under /opt, depending on the language. Structure your layer so that function code can access libraries without additional configuration. You can also use the AWS Serverless Application Model (AWS SAM) to manage layers and your function's layer configuration.
