Elastic Beanstalk worker environments support Amazon Simple Queue Service (SQS) dead letter queues. A dead letter queue is a queue where other (source) queues can send messages that for some reason could not be successfully processed. A primary benefit of using a dead letter queue is the ability to sideline and isolate the unsuccessfully processed messages. You can then analyze any messages sent to the dead letter queue to try to determine why they were not successfully processed.
http://docs.aws.amazon.com/elasticbeanstalk/latest/dg/using-features-managing-env- tiers.html#worker-d eadletter

Explanation
The below snapshot from the AWS documentation gives details on the Networkln metric

Explanation
Elastic Beanstalk supports the deployment of web applications from Docker containers. With Docker containers, you can define your own runtime environment. You can choose your own platform, programming language, and any application dependencies (such as package managers or tools), that aren't supported by other platforms. Docker containers are self-contained and include all the configuration information and software your web application requires to run.
By using Docker with Elastic Beanstalk, you have an infrastructure that automatically handles the details of capacity provisioning, load balancing, scaling, and application health monitoring.
For more information on Dockers and Elastic beanstalk please refer to the below link:
* http://docs.aws.amazon.com/elasticbeanstalk/latest/dg/create_deploy_docker.html