This interface supports integration between designate-bind and prometheus-bind-exporter-operator.

To consume this interface in your charm or layer, add the following to layer.yaml:

includes: ['interface:bind-client']

and add a requires interface of type bind-client to your charm or layers metadata.yaml:

requires:
  bind-stats:
    interface: bind-client

This flag is set when the subordinate unit is joined and removes when departed.

For example, the following code will update the relation just when the relation is estabilished and the configuration changed:

if reactive.is_flag_set('bind-stats.available'):
        config = hookenv.config()
        if config.changed("stats-port") or config.changed("stats-listen-net"):
            relation_settings = {
                'stats-listen-net': hookenv.config('stats-listen-net'),
                'stats-port': hookenv.config('stats-port')
            }
            for rel_id in hookenv.relation_ids('bind-stats'):
                hookenv.relation_set(
                    rel_id,
                    relation_settings=relation_settings
                )

When this flag is set, it will create a new file /etc/bind/stats.conf in charm-designate-bind with the following content:

statistics-channels {
  inet <stats-listen-net> port <stats-port> allow { <client-ip>; };
};

It will also include this new file at etc/bind/named.conf. This will open a statistics channel in bind that prometheus-bind-exporter can expose metrics for prometheus to collect.

When the flag is not set, the statistics channel is closed.