Keeping Razor scalable

Speed provisioning and reduce load on the Razor server by following these scalability best practices.

When creating repos, use url rather than iso-url. If you have a mirror hosting installation files, they can be distributed straight to the node rather than having the Razor server distribute the files.
When matching policies, limit the number of tags you use.
- Create tags using the has_macaddress operator to identify a list of nodes to be assigned the tag, for example, ["has_macaddress", "de:ea:db:ee:f0:00", "de:ea:db:ee:f0:01"].
- Set the policy metadata key on nodes using the modify-node-metadata command, then create matching tags, for example, ["=", ["metadata", "policy"], "policy1"].
When running hooks, avoid long- and frequent-running scripts, which all run on the same thread synchronously.