Exploring how instances retrieve their metadata
In Chapter 3, Installing Neutron, we briefly covered the process of instances accessing metadata over the network: either through a proxy in the router namespace or the DHCP namespace. The latter is described in the following section.
The DHCP namespace
Instances access metadata at http://169.254.169.254, followed by a URI that corresponds to the version of metadata, which is usually/latest. When an instance is connected to a network that does not utilize a Neutron router as the gateway, the instance must learn how to reach the metadata service. This can be accomplished in a few different ways, including the following:
- Setting a route manually on the instance
- Allowing DHCP to provide a route
When enable_isolated_metadata is set to True in the DHCP configuration file at /etc/neutron/dhcp_agent.ini, each DHCP namespace provides a proxy to the metadata service running on the controller node(s). The proxy service listens directly on port 80, as shown...
