DHCP Not Discovering Nodes if Set as Static
Introduction
Warewulf configures an external DHCP service to direct cluster nodes how to boot from Warewulf. In its default configuration, Warewulf uses a DHCP pool to provision cluster nodes, after which they transition to the permanent IP address configured in the node registry.
⚠️ WARNING The DHCP range must not overlap with the addresses that are assigned to nodes in the node registry.
To define the desired range of IP addresses to lease during the boot process, update dhcp.range start and dhcp.range end.
dhcp:
range start: 10.0.0.100
range end: 10.0.0.110
NOTE: The DHCP range is only used while a node is provisioning, and its size determines how many nodes can provision simultaneously. For example, a large cluster of thousands of nodes may be provisioned in batches of 32 nodes, so a DHCP pool of 32 addresses should be sufficient.
Warewulf may alternatively also be configured to provide static DHCP addresses based on individual node configurations. This requires additional administrative overhead, as the DHCP configuration must be updated when nodes are added to the cluster. It removes the need for a DHCP address pool to be separate from the assigned cluster node IP addresses.
# warewulf.conf
dhcp:
template: static
The Warewulf daemon should be restarted after the changes made to warewulf.conf, and the DHCP service must be reconfigured to generate the necessary static DHCP host entries.
$ systemctl restart warewulfd
$ wwctl configure dhcp
Building overlay for wwctl1: host
Enabling and restarting the DHCP services
$ grep --after-context=5 '^host n1-default' /etc/dhcp/dhcpd.conf
host n1-default
{
hardware ethernet 5a:00:05:23:eb:c6;
fixed-address 10.0.0.111;
option host-name "n1";
}
Problem
Some users may try to change the dhcp.template option to static instead of the default config. As mentioned, it will require extra management to configure it the first time. This may cause the nodes to be unable to boot, as it may miss required information that has to be manually added in the /etc/dhcpd.conf file.
Resolution
The DHCP configuration is only for booting the node. The best practice is to set the dhcp.template: to default and let the node boot with autodiscovery. Once it boots, it will get the IP address that was set on the node configuration. When this happens, Warewulf will save the MAC address in the node.conf file, and it will be easier to switch dhcp.template: to static in the future.