Name resolution for instances

updated: None

Name resolution for instances

Name resolution for instances¶

The Networking service offers several methods to configure name resolution (DNS) for instances. Most deployments should implement case 1 or 2. Case 3 requires security considerations to prevent leaking internal DNS information to instances.

Case 1: Each virtual network uses unique DNS resolver(s)¶

In this case, the DHCP agent offers one or more unique DNS resolvers to instances via DHCP on each virtual network. You can configure a DNS resolver when creating or updating a subnet. To configure more than one DNS resolver, use a comma between each value.

Configure a DNS resolver when creating a subnet.
```
$ neutron subnet-create --dns-nameserver DNS_RESOLVER
```
Replace DNS_RESOLVER with the IP address of a DNS resolver reachable from the virtual network. For example:
```
$ neutron subnet-create --dns-nameserver 203.0.113.8,198.51.100.53
```
Note

This command requires other options outside the scope of this content.
Configure a DNS resolver on an existing subnet.
```
$ neutron subnet-update --dns-nameserver DNS_RESOLVER SUBNET_ID_OR_NAME
```
Replace DNS_RESOLVER with the IP address of a DNS resolver reachable from the virtual network and SUBNET_ID_OR_NAME with the UUID or name of the subnet. For example, using the selfservice subnet:
```
$ neutron subnet-update --dns-nameserver 203.0.113.8,198.51.100.53 selfservice
```

Case 2: All virtual networks use same DNS resolver(s)¶

In this case, the DHCP agent offers the same DNS resolver(s) to instances via DHCP on all virtual networks.

In the dhcp_agent.ini file, configure one or more DNS resolvers. To configure more than one DNS resolver, use a comma between each value.
```
[DEFAULT]
dnsmasq_dns_servers = DNS_RESOLVER
```
Replace DNS_RESOLVER with the IP address of a DNS resolver reachable from all virtual networks. For example:
```
[DEFAULT]
dnsmasq_dns_servers = 203.0.113.8, 198.51.100.53
```
Note

You must configure this option for all eligible DHCP agents and restart them to activate the values.

Case 3: All virtual networks use DNS resolver(s) on the host¶

In this case, the DHCP agent offers the DNS resolver(s) in the resolv.conf file on the host running the DHCP agent via DHCP to instances on all virtual networks.

In the dhcp_agent.ini file, enable advertisement of the DNS resolver(s) on the host.
```
[DEFAULT]
dnsmasq_local_resolv = True
```
Note

You must configure this option for all eligible DHCP agents and restart them to activate the values.

updated: None

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