Backend definition in multiple VCL files in Varnish 5

[Kurt Sultana]

Hi all,

I'm a bit newish to Varnish though I do have some background. I have a
Varnish 5 instance connected to 2 backend servers (Magento 2 applications).

I'm using the new Varnish 5 feature of loading multiple VCL files. My
ultimate problem is during purging however I'd like to ensure things are
set up correctly because documentation regarding multiple VCL files in
Varnish 5 is somewhat lacking.

To keep things very simple for now, I'm going to use 1 backend server in my
example.

So, I have a magento.vcl defined as follows:

*vcl 4.0;*

*import std;*

*# The minimal Varnish version is 4.0*
*# For SSL offloading, pass the following header in your proxy server or
load balancer: 'X-Forwarded-Proto: https'*

*backend default {*
*    .host = "127.0.0.1";*
*    .port = "8088";*
*}*

*include "/etc/varnish/common.vcl";*

And a top.vcl

*vcl 4.0;*

*import std;*

*backend default { .host = "127.0.0.1"; }*

*sub vcl_recv {*
*    if (req.http.host == "magento2.dev") {*
*        return (vcl(magento_vcl));*
*    }*
*}*

Then I run

*service varnish restart*

*varnishadm*

*vcl.load magento /etc/varnish/conf.d/magento.vcl*

*vcl.label magento_vcl magento *

*vcl.load top /etc/varnish/top.vcl*

*vcl.use top*

*quit*

When I browse to magento2.dev, I get a backend fetch error after some
seconds. It's only when I go in magento.vcl and change the name of the
backend and make a backend hint that it works. See below:

*vcl 4.0;*

*import std;*

*# The minimal Varnish version is 4.0*
*# For SSL offloading, pass the following header in your proxy server or
load balancer: 'X-Forwarded-Proto: https'*

*backend magento {*
*    .host = "127.0.0.1";*
*    .port = "8088";*
*}*

*sub vcl_recv {    set req.backend_hint = magento;}*

*include "/etc/varnish/common.vcl";*

Why should I be specifying a backend hint? Shouldn't Varnish be loading a
different VCL according to the host specified in top.vcl? Or is there
something wrong?

Thanks in advance,
Kurt
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