An ADC or Application Delivery Controller is a Layer 7 Load Balancer with HTTP and SSL acceleration, Web App Firewalling and other security features. Think of ADCs as Load Balancers on steroids, with a specific focus on websites and applications.
In Nova one or more ADCs can be attached to one or more Nodes. This allows you to effectively link an ADC configuration with a set of Nodes to run it on.
For example, I may create an ADC for load balancing and accelerating a website on port 80 and port 443 (SSL termination ADC). Then I may launch two Nodes, and attach the ADC to both. Now both of those Nodes will accept traffic on port 80 (HTTP) and port 443 (HTTPS) and send that traffic to a selected backend.
To learn more about ADCs and Backends on Nova please continue with the guide: