Ttyjfyk

Is possible with Varnish configure multiple backends for one site? For example I have high avalibility site with multiple backends.

For example I have site www.goodies.com which is running on php 5.6. So I have 3 www-nodes as backend www-node5.6a www-node5.6b www-node5.6c

I have configured backends in Varnish like this:

backend www-node5.6a 
 .host = "10.0.0.11";
 .port = "80";
 .connect_timeout = 6000s;
 .first_byte_timeout = 6000s;
 .between_bytes_timeout = 6000s;


backend www-node5.6b 
 .host = "10.0.0.12";
 .port = "80";
 .connect_timeout = 6000s;
 .first_byte_timeout = 6000s;
 .between_bytes_timeout = 6000s;


backend www-node5.6c 
 .host = "10.0.0.13";
 .port = "80";
 .connect_timeout = 6000s;
 .first_byte_timeout = 6000s;
 .between_bytes_timeout = 6000s;

my question is, how to configure Varnish so user will be randomly use to any of this backends for this specific one site?

What you are looking for if you want random distribution of the content you need something like this in your config file:

director cl1 random 
 .backend = [Backend0]; .weight = 1; 
 .backend = [Backend1]; .weight = 1; 

More information about how Varnish backends work can be found here. I found the above snippet from this blog. You can also do this on the basis of url, as seen here. You can also read more on configuring Varnish for High Availability here.

You should consider doing health checks and setting up and defining an actual director in round robin mode. Random is random. In theory, every single user that visits your site could be randomly sent to the same backend and that would be just as "random" as splitting things evenly based on backend health and status. Looking to another source they have something along these lines:

import directors; 

backend [Backend0] 
 .host = "192.168.0.10";
 .probe = 
 .url = "/";
 .timeout = 1s;
 .interval = 5s;
 .window = 5;
 .threshold = 3;
 

backend [Backend1] 
 .host = "192.168.0.10";
 .probe = 
 .url = "/";
 .timeout = 1s;
 .interval = 5s;
 .window = 5;
 .threshold = 3;
 

sub vcl_init 
 new vdir = directors.round_robin();
 vdir.add_backend([Backend0]);
 vdir.add_backend([Backend1]);
 

Make the changes as necessary for what makes sense in your environment. Please read over all the links and documentation as well as make a backup of your old configuration before trying any of this.