Using multiple backends in Varnish

Thu, 02 Sep 2021 00:00:00 +0000

The most common Varnish setups will feature a single backend, as illustrated in the VCL snippet below:

vcl 4.1;

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

However it is also possible to define multiple backends and to use VCL logic to decide which backend to use.

VCL example

The example below has 2 backends:

default that connects to backend.example.com on port 80
image that connects to image.example.com on port 80

The image backend in the example is only used when the URL ends with .png, .jpg or .svg.

Using basic authentication in VCL backend probes

Fri, 01 Oct 2021 00:00:00 +0000

When your Varnish server proxies requests to a backend that requires authorized access via basic authentication, you need to ensure that the right Authorization header is sent for each probe request.

1. Initial situation

Your initial backend setup will have a backend that may contain a .probe {} definition.

This health-checking probe will send HTTP requests to your backend server at regular intervals. As long as a 200 status code is returned, the backend is considered healthy.

Backend on Varnish Cache

Using multiple backends in Varnish

VCL example

Using basic authentication in VCL backend probes

1. Initial situation