Backend servers

Varnish has a concept of “backend” or “origin” servers. A backend server is the server providing the content Varnish will accelerate.

Our first task is to tell Varnish where it can find its content. Start your favorite text editor and open the varnish default configuration file. If you installed from source this is /usr/local/etc/varnish/default.vcl, if you installed from a package it is probably /etc/varnish/default.vcl.

Somewhere in the top there will be a section that looks a bit like this.:

# backend default {
#     .host = "127.0.0.1";
#     .port = "8080";
# }

We comment in this bit of text and change the port setting from 8080 to 80, making the text look like.:

backend default {
      .host = "127.0.0.1";
      .port = "80";
}

Now, this piece of configuration defines a backend in Varnish called default. When Varnish needs to get content from this backend it will connect to port 80 on localhost (127.0.0.1).

Varnish can have several backends defined and can you can even join several backends together into clusters of backends for load balancing purposes.

Now that we have the basic Varnish configuration done, let us start up Varnish on port 8080 so we can do some fundamental testing on it.