When it comes to building a truly web-scale network, Layer 2 just doesn'tcut it anymore. Extending Layer 3 down to the hosts by running a routing suite such as Quagga makes it possible to oversubscribe servers to an arbitrarily high number of top of rack switches and again to the aggregation layer.
Docker is a software delivery system built around a technology called "containers", which are very lightweight alternative to virtual machines. Docker makes it possible to deliver software like the Cumulus Linux version of Quagga to servers in a cross-platform way. This demo shows how to install and configure a fully layer 3 network with Quagga running on the hosts using Ansible.