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 configuration file using the dnsmasq_config_file configuration option. For example:

dnsmasq_config_file=/etc/dnsmasq-nova.conf

For an example of how to change the behavior of dnsmasq using a dnsmasq configuration file, see the OpenStack Configuration Reference. The dnsmasq documentation also 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

Logging output for dnsmasq goes to the syslog (typically /var/log/syslog or /var/log/messages, depending on Linux distribution). 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. This reservation only affects which IP address the VMs start at, not the fixed IP addresses that the nova-network service places on the bridges.