The CNI plugin is responsible wiring up the container. That is – it needs to do all the work to get the container on the network. In Docker, this would include connecting the container network namespace back to the host somehow.

Why is CNI needed?

If you are working on latency-sensitive applications, the AWS-CNI plugin allows accepting traffic directly to your pods. AWS-CNI plugin creates a virtual network interface on the host instance and creates a network route directly to the pods. This property can help decrease the network latency.

What is a CNI container?

The Container Network Interface (CNI) is a container networking specification proposed by CoreOS and adopted by projects such as Apache Mesos, Cloud Foundry, Kubernetes, Kurma and rkt. There are also plugins created by projects such as Contiv Networking, Project Calico and Weave.