A couple of years ago we introduced the real-time statistics API with VAC. Varnish Cache provides a lot of statistics on website activity; however, in order to obtain this information it must be pulled from each server manually. Additionally, they are not available in real time. Meanwhile, Varnish Administration Console provides valuable real-time analytics across multiple instances.
When managing several Varnish instance(s), keeping the configuration coherent between them can be hard. Monitoring and deploying configuration, restarting the instances in a synchronized fashion requires some knowledge. The Varnish Administration Console (VAC) , provides a full API that helps leveraging once difficult tasks.