DHCP lease scanning and DNS

Overview

In a MAAS system, cluster controllers may optionally manage the DHCP, and the region controller may optionally manage the DNS.

The region controller periodically tells the cluster controllers to report their DCHP leases. When a cluster controller reports new leases, the region controller creates DNS records for them, and instructs the cluster controller to convert the leases to static host mappings.

Leases scanning

MAAS will periodically scan the DHCP leases file using the upload_dhcp_leases() celery task, which originates via celerybeat.

As leases are discovered, it calls the api function update_leases() which will subsequently generate a new task called add_new_dhcp_host_map() that will use omshell to write a permanent mapping from MAC to IP in the DHCP server.

That host map remains until the node is deleted, at which point the remove_dhcp_host_map() task is invoked which uses omshell to remove the map.

Updating the DNS zone file

If a new lease is found then the dns.change_dns_zones() function gets called which invokes two tasks:

#. ``write_dns_zone_config()``
#. ``rndc_command()``

The first is responsible for writing out a new zone file with the appropriate sequence number and timestamp, and then the second is chained on to that and sends an rndc message to the DNS server to reload the zone.