DHCP server: dnsmasq

The Compute service uses dnsmasq as the DHCP server when running with either that Flat DHCP Network Manager or the VLAN Network Manager. The nova-network service is responsible for starting up dnsmasq processes.

The behavior of dnsmasq can be customized by creating a dnsmasq configuration file. Specify the config file using the dnsmasq_config_file configuration option. For example:

dnsmasq_config_file=/etc/dnsmasq-nova.conf

See the high availability section for an example of how to change the behavior of dnsmasq using a dnsmasq configuration file. The dnsmasq documentation has a more comprehensive dnsmasq configuration file example.

Dnsmasq also acts as a caching DNS server for instances. You can explicitly specify the DNS server that dnsmasq should use by setting the dns_server configuration option in /etc/nova/nova.conf. The following example would configure dnsmasq to use Google's public DNS server:

dns_server=8.8.8.8

Dnsmasq logging output goes to the syslog (typically /var/log/syslog or /var/log/messages, depending on Linux distribution). The dnsmasq logging output can be useful for troubleshooting if VM instances boot successfully but are not reachable over the network.

A network administrator can run nova-manage fixed reserve --address=x.x.x.x to specify the starting point IP address (x.x.x.x) to reserve with the DHCP server, replacing the flat_network_dhcp_start configuration option that was available in Diablo.