it is recommended to install the latest version

sudo curl http://repo.varnish-cache.org/debian/GPG-key.txt | sudo apt-key add -
 
# add the repo
sudo nano /etc/apt/sources.list
deb http://repo.varnish-cache.org/ubuntu/ lucid varnish-3.0
 
sudo apt-get update
sudo apt-get install varnish

configuration basic:

sudo nano /etc/default/varnish
 
 DAEMON_OPTS="-a :80 \
             -T localhost:6082 \
             -f /etc/varnish/default.vcl \
             -S /etc/varnish/secret \
             -s malloc,256m"
 
# tell varnish to look for the content on localhost port 8080.
sudo nano /etc/varnish/default.vcl
backend default {
    .host = "127.0.0.1";
    .port = "8080";
}
 
 
sudo nano /etc/apache2/ports.conf
 
NameVirtualHost 127.0.0.1:8080
Listen 127.0.0.1:8080
 
sudo nano /etc/apache2/sites-available/default
<VirtualHost 127.0.0.1:8080>
 
# reload the services
sudo service apache2 restart
sudo service varnish restart

maintenance command

varnishstat