instance hostname not getting resolved locally ?

asked 2016-08-03 06:13:26 -0500

unmeshdesale
11 ●1 ●1 ●2

I am using liberty with neutron running on controller nodes in HA. Instance is properly getting private ip address and I am able to resolve http://google.com from instance but when I try to resolve instance's hostname, I am getting below error.

Instance details

host-10-10-0-101:~ # nslookup host-10-10-0-101
Server:         172.16.8.2
Address:        172.16.8.2#53

** server can't find host-10-10-0-101: NXDOMAIN

host-10-10-0-101:~ # ping host-10-10-0-101
ping: unknown host host-10-10-0-101

host-10-10-0-101:~ # cat /etc/hosts
127.0.0.1  localhost.rmnus.sen.symantec.com localhost localhost
::1     localhost.rmnus.sen.symantec.com localhost localhost ip6-localhost ip6-loopback

host-10-10-0-101:~ # cat /etc/resolv.conf

search openstacklocal
nameserver 172.16.8.2
nameserver 172.16.8.3

DNSMASQ running on controller node

nobody    37679      1  0 04:33 ?        00:00:00 dnsmasq --no-hosts --no-resolv --strict-order --except-interface=lo --pid-file=/var/lib/neutron/dhcp/8822445d-2185-4b7b-97bc-ee26318c71fa/pid --dhcp-hostsfile=/var/lib/neutron/dhcp/8822445d-2185-4b7b-97bc-ee26318c71fa/host --addn-hosts=/var/lib/neutron/dhcp/8822445d-2185-4b7b-97bc-ee26318c71fa/addn_hosts --dhcp-optsfile=/var/lib/neutron/dhcp/8822445d-2185-4b7b-97bc-ee26318c71fa/opts --dhcp-leasefile=/var/lib/neutron/dhcp/8822445d-2185-4b7b-97bc-ee26318c71fa/leases --dhcp-match=set:ipxe,175 --bind-interfaces --interface=tap60be5562-46 --dhcp-range=set:tag0,10.10.0.0,static,600s --dhcp-option-force=option:mtu,1416 --dhcp-lease-max=65536 --conf-file= --server=172.16.8.2 --server=172.16.8.3 --domain=openstacklocal

root@controller-01:~# cat /var/lib/neutron/dhcp/8822445d-2185-4b7b-97bc-ee26318c71fa/host
fa:16:3e:1e:8a:4a,host-10-10-0-10.openstacklocal.,10.10.0.10
fa:16:3e:00:82:73,host-10-10-0-21.openstacklocal.,10.10.0.21
fa:16:3e:0d:21:97,host-10-10-0-101.openstacklocal,10.10.0.101

This instance doesn't have cloud-init thats why it gets hostname from dnsmasq generated by neutron. Instance should be able to resolve itself and ping itself using it's own hostname. This was working fine on nova-network. How does neutron handle DNS resolution of instance hostname specifically in this case instance has got the hostname generated by neutron?

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2 answers

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answered 2016-08-25 05:48:33 -0500

sunnyarora
491 ●2 ●4 ●10

External "Designate" server is the solution you are looking for which you will need to combine with Neutron network.

The issue which you are facing of not resolveing the dns name, its root cause is the way internal Neutron DHCP implemented. Broadly speaking, Instance gets DHCP from the network node. There are different agents associated with Neutron like plugin agent, DHCP agent,l3 agent etc. These agents interact with the main neutron process through RPC (for ex RabbitMQ or Qpid) or through the standard Networking API.

For each network, there is dnsmasq instance which provides DHCP services and DNS services. The namespace is like qdhcp-<uuid>. That UUID is of the network.

What happens in the background : Whenver a port is created in Neutron server -> Neutron server notifies the DHCP Agent that new port has been created and that point DHCP agent requests via RPC channel for port information and from that information It Creates a file/data no.of files that dnsmasq uses to comeup with the DHCP allocation and DNS services for that port. The DHCP agent notifies dnsmasq that it needs to read that file/files. Then DHCP agent creates such hostname with mix of IP address like "Host-'I-P'".