Allow multiple CLI bindings

[wonko]

:person_frowning: Problem Statement

In certain cases, it's needed to supply multiple CLI binding addresses/ports. One example is when a private network is being used to connect the caching layer to webservices. The webservice layer needs to be able to set bans (or ...), while it might also be needed to still connect from localhost.

❔ Possible Solution

Currently, the address and the port are single entries, separated. It suggest to make this a single item (host and port), but to allow an array.

varnish_config 'default' do 
 ...
 admin_listen_bindings ['127.0.0.1:6082', '192.168.0.1:60820']
...
end

This would then be translated towards the correct startup parameters as varnishd allows to add multiple CLI bindings:

root@web-003:~# varnishd -? | grep -A1 -- -T 
varnishd: invalid option -- '?'
  -T address[:port]            # CLI address
                               # Can be specified multiple times.

See https://github.com/sous-chefs/varnish/blob/main/templates/default_systemd.erb#L31

The old parameters can be added to the array as the only option, if no bindings are supplied.

⤴️ Describe alternatives you've considered

No way of doing this decently without seriously dirty fiddling (adding a value for port with a portnumber, a space, a -T followed with a second binding ... but I'd consider this as being a dirty hack).

Another alternative is to bind to '*' and then to add firewalling rules to block this. However, I find this bad practice, and it takes away the possibility to allow multiple ports to be used.