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Access to metadata process is how, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain for you in detail, people with this need can come to learn, I hope you can gain something.

After starting neutron router, instance C1 finally got the metadata

C1 thinks that the metadata service address is 169.254.169.254 and the port is 80. Let's try to access metadata in C1.

You can really get metadata. But we know that nova-api-metadata runs on the control node, and IP is not 169.254.169.254. How is this achieved? Let's analyze this process.

The request for access to 169.254.169.254 from the routing table of C1 will go 17.17.17.1.

17.17.17.1 is actually the interface IP of test_router on test_net. This route is automatically added by OpenStack to instance, which forwards metadata's request to neutron router.

Ip netns is the command to manage linux network namespace. If you are not familiar with namespace, you can refer to the previous chapter of the tutorial.

Test_router receives a request from C1 and forwards it to port 9697 through iptable rules.

What is port 9697 for? This is the listening port of neutron-ns-metadata-proxy.

At this point, we can reorganize our thinking:

Instance requests metadata through the predefined 169.254.169.254.

The request is forwarded to neutron router.

Router forwards the request to neutron-ns-metadata-proxy.

Then it's simple: neutron-ns-metadata-proxy sends the request to neutron-metadata-agent through unix domain socket, which in turn sends it to nova-api-metadata through the management network.

OpenStack creates and manages neutron-ns-metadata-proxy through l3-agent by default. But not all environments have l3-agent, such as scenarios where physical router is used directly. At this point, you need to let dhcp-agent manage the neutron-ns-metadata-proxy.

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