Domains: put a limit of 2 custom domains per project

Related #1808

Author: humitos

readthedocs/projects/models.py

@@ -36,6 +36,7 @@
 from readthedocs.core.utils import extract_valid_attributes_for_model, slugify
 from readthedocs.core.utils.url import unsafe_join_url_path
 from readthedocs.domains.querysets import DomainQueryset
+from readthedocs.domains.validators import check_domains_limit
 from readthedocs.notifications.models import Notification as NewNotification
 from readthedocs.projects import constants
 from readthedocs.projects.exceptions import ProjectConfigurationError
@@ -1817,6 +1818,9 @@ def restart_validation_process(self):
             self.validation_process_start = timezone.now()
             self.save()
 
+    def clean(self):
+        check_domains_limit(self.project)
+
     def save(self, *args, **kwargs):
         parsed = urlparse(self.domain)
         if parsed.scheme or parsed.netloc:

readthedocs/settings/base.py

@@ -170,7 +170,8 @@ def RTD_DEFAULT_FEATURES(self):
 
         return dict(
             (
-                RTDProductFeature(type=constants.TYPE_CNAME).to_item(),
+                # Max number of domains allowed per project.
+                RTDProductFeature(type=constants.TYPE_CNAME, value=2).to_item(),
                 RTDProductFeature(type=constants.TYPE_EMBED_API).to_item(),
                 # Retention days for search analytics.
                 RTDProductFeature(