You can prevent users from creating zones with names that match a
particular regular expression using blacklists. For example, you might
use a blacklist to prevent users from:

• creating a specific zone.
• creating zones that contain a certain string,
• creating subzones of a certain zone.

Managing Blacklists

You can create blacklists using the
zone blacklist create command with System
Administrator privileges. For example, to blacklist
example.com. and all of its subdomains:

$ openstack zone blacklist create --pattern ".*example.com."
+-------------+--------------------------------------+
| Field       | Value                                |
+-------------+--------------------------------------+
| created_at  | 2021-05-27T04:06:42.000000           |
| description | None                                 |
| id          | 7622e241-8c3d-4c03-a692-8747e3cf2658 |
| pattern     | .*example.com.                       |
| updated_at  | None                                 |
+-------------+--------------------------------------+

If a Domain
or Project Persona attempts to create foo.example.com.,
or example.com., they encounter an error:

$ openstack zone create --email [email protected] example.com.
Blacklisted zone name
$ openstack zone create --email [email protected] foo.example.com.
Blacklisted zone name

You can update a blacklist using zone blacklist set to
modify its pattern or description;

$ openstack zone blacklist set 81fbfe02-6bf9-4812-a40e-1522ab6862ca --pattern ".*web.example.com"
+-------------+--------------------------------------+
| Field       | Value                                |
+-------------+--------------------------------------+
| created_at  | 2021-05-27T04:14:14.000000           |
| description | None                                 |
| id          | 81fbfe02-6bf9-4812-a40e-1522ab6862ca |
| pattern     | .*web.example.com                    |
| updated_at  | 2021-05-27T04:14:48.000000           |
+-------------+--------------------------------------+

You can delete a blacklist using `zone blacklist delete`:

$ openstack zone blacklist delete 7622e241-8c3d-4c03-a692-8747e3cf2658

There is no output when this command is successful.

Using the REST API

The regular expressions used for blacklists are similar to Python
regular expressions, but you must escape certain characters when making
HTTP calls.

For examples, this refex restricts using example.com.
and its ASCII subdomains:

^([A-Za-z0-9_\\-]+\.)*example\.com\.$

However, you must insert the escape character (backslash, ) before
the instances of dot (.) and .com:

^([A-Za-z0-9_\\-]+\\.)*example\\.com\\.$

Here is the API call and the regex with the HTTP characters
escaped:

POST /v2/blacklists/ HTTP/1.1
Accept: application/json
Content-Type: application/json

{
  "pattern" : "^([A-Za-z0-9_\\-]+\\.)*example\\.com\\.$",
  "description" : "This blacklists *.example.com."
}

Regular Expressions

Regular Expressions can be difficult to work with. The Python
Regex Documentation may serve as a useful introduction, and online
regular expression tools can assist when building and testing regexes
for use with the blacklist API.