There is an Elastic Beanstalk-only configuration file called Dockerrun.aws.json. This file is used to configure single or multi-container deployments on Elastic Beanstalk.

For a single-container deployment, Elastic Beanstalk can work with either a Dockerfile or a Dockerrun file.

For a multi-container deployment, Elastic Beanstalk can only work with a Dockerrun file.

These docs may come in handy.

• Single-container Deployment
• Multi-container Deployment