How to block an IP address or network block with Varnish VCL

I've not seen that specific error, but, when putting a backend in, I have noticed if the backend isn't referenced within the config, it has given me problems when restarting on our development servers.

storage_file: filename: /var/lib/varnish/devel/varnish_storage.bin size 1024 MB.
Message from VCC-compiler:
Unused backend default2, defined:
(input Line 11 Pos 9)
backend default2 {
--------########--
Running VCC-compiler failed, exit 1
VCL compilation failed

So, is it possible that you have no rule referencing the backend?

No, there isn't (I just checked 1 hour ago). You can comment the bind-address in my.cnf:

Note: « 1 hour ago » is now more than 10 years ago.

#skip-networking
#bind-address                   = 127.0.0.1

If you want only 2 IPs, you will then have to use a firewall.

For MySql version 8.0.13 and above, you can specify a list of comma-separated IP addresses.

bind-address = 10.0.0.1,10.0.1.1,10.0.2.1

Relevant MySql documentation.

Remember to restart your MySQL instance after changing the config file.