Goal

• named supports multiple versions of a given zone. When it is loading a new zone data after reconfiguration, it still answers with previous zone data to clients. Even on startup, it will answer SERVFAIL in given zone, until its asynchronous loading does not finish. Then it finishes zone content loading, switches version to last one and drops the old one, once no clients have open reference to that database.
• Our current bind-dyndb-ldap has only current zone. When reconfiguration happens, it will forget all zones it were authoritative for. Then fetches the zone list from LDAP mixed with data. It can respond to queries even in the middle of data loading. It could lead to wrong answers that some record does not exist, when it were not yet loaded.
• Implement some signal that zones and their data are loaded. Only on that signal switch previous content to newly fetched data. 
  • For example: As a user, I Want receive SERVFAIL until named has loaded whole zone content, util it has finished loading. The same way named does it with classic text records.
  • If there were incoming dynamic DNS updates during LDAP is still fetching a zone, they have to be replayed on top of fetched zone.

Acceptance criteria

A list of verification conditions, successful functional tests, or expected outcomes in order to declare this story/task successfully completed.

• Verify named knows when zones loaded all data and is waiting only for updates
• Verify named will serve SERVFAIL until it has finished loading
• Verify named will serve zone data even during reload, until it has loaded a new version.