Comment 1 for bug 1850182

I've reproduced this with the following:

Deployed the bundle from charm-designate-bind/src/tests/bundles/focal-ussuri.yaml
Created zone with:
openstack zone create --debug --email <email address hidden> mysite.com.
Added A record in the zone:
openstack recordset create --type A --record 10.5.0.1 mysite.com. gw.mysite.com.
Looked up the record in designate-bind:
dig gw.mysite.com @10.5.0.7
    gw.mysite.com. 3600 IN A 10.5.0.1
Add a new unit with:
juju add-unit designate-bind
looked up the record on the new server after the model settles:
dig gw.mysite.com @10.5.0.12
    ;; WARNING: recursion requested but not available

When I look at the new unit, the slave.zone file has been created but is blank due to rndc RBAC failures.

I'm pulling a juju-crashdump now to attach to the bug.