allow binding on a specific IP or interface

[Junien F]

Hi,

I need to bind the prometheus output port of telegraf to a specific interface/IP, but the charm doesn't let you do that.

You could specify an IP in prometheus_output_port or extra_options, but this doesn't work so well when multiple units are deployed.

Ideally, we should be able to configure an interface or a network to allow telegraf to bind on it.

The following should be accepted :
juju config telegraf prometheus_output_port=eth0:1234
juju config telegraf prometheus_output_port=10.1.2.0/24:1234
juju config telegraf prometheus_output_port=fe80:1::/64:1234

Maybe a new config option could be added instead of piggybacking on the prometheus_output_port one, for example prometheus_output_interface (or bindaddress or something).

Then the charm would find the IP on this interface (or on this network) and would bind on it.

Thanks !