Exploring how instances retrieve their metadata
In Chapter 3, Installing Neutron, I briefly discussed the process of how metadata is provided to instances through the Neutron metadata proxy. There are two ways in which an instance can get its metadata over the network: through the router namespace or through the DHCP namespace. Both methods are described in the upcoming sections.
Router namespace
Although routers will be described and configured in the next chapter, it is important to know their function with regard to metadata. Neutron assumes that when a gateway IP is set on a subnet, one of the following two things is true:
The gateway IP belongs to a Neutron router
The specified gateway will handle all the routing requests from instances, including those to the metadata server
When a subnet is connected to a Neutron router that is serving as the gateway for that subnet, the router is responsible for routing all traffic from the subnet, including traffic to the metadata service. When instances...
