EFS or Elastic File System is an AWS service offering a fully managed elastic and shared file system that can be integrated with other AWS services.
Up until now it was not possible to use EFS with Lambda directly but now AWS released EFS for Lambda functions and this solves another big inconvenience while working with Lambda functions: the disk size and persistence.
This video shows you how to use the EFS (Elastic File System) from within AWS Lambda. The example code is written in Nodejs.