Varnish is an HTTP accelerator and a useful tool for speeding up a server, especially during a times when there is high traffic to a site. It works by redirecting visitors to static pages whenever possible and only drawing on the virtual private server itself if there is a need for an active process.
How to Install Varnish
Varnish is distributed in the Ubuntu package repositories, but the version there might be out of date, so the varnish site recommends installing the varnish package through their repository.
1) Start that process by grabbing the repository:
sudo curl http://repo.varnish-cache.org/debian/GPG-key.txt | sudo apt-key add –
2) To add the repository to the list of apt sources. Go ahead and open up that file.
sudo nano /etc/apt/sources.list
3) Add the varnish repository to the list of sources.
deb http://repo.varnish-cache.org/ubuntu/ lucid varnish-3.0
4) Save and exit
Congrats , Update apt-get and install varnish.
sudo apt-get update
sudo apt-get install varnish