Varnish Custom Statistics gives you granular and detailed cache and performance metrics on the contents of your cache and its associated traffic.
VCS produces real-time aggregated statistics from a group of Varnish servers. The statistics produced are then grouped according to keys defined in VCL and presented in time series.
VCS is split into 2 components:
vcsserver. This component is the main database, UI, and API server for VCS. This should be installed on a separate server. It can be installed on the same server as VAC.
vcs-agent. This component is installed on each of your Varnish servers. They connect and push data to the
Please click here for VCS 4.0 documentation.