How to integrate with systemd-resolved

If the system that runs Incus uses systemd-resolved to perform DNS lookups, you should notify resolved of the domains that Incus can resolve. To do so, add the DNS servers and domains provided by an Incus network bridge to the resolved configuration.

Note

The dns.mode option (see Configuration options) must be set to managed or dynamic if you want to use this feature.

Configure resolved

To add a network bridge to the resolved configuration, specify the DNS addresses and domains for the respective bridge.

DNS address

You can use the IPv4 address, the IPv6 address or both. The address must be specified without the subnet netmask.

To retrieve the IPv4 address for the bridge, use the following command:

incus network get <network_bridge> ipv4.address

To retrieve the IPv6 address for the bridge, use the following command:

incus network get <network_bridge> ipv6.address

DNS domain

To retrieve the DNS domain name for the bridge, use the following command:

incus network get <network_bridge> dns.domain

If this option is not set, the default domain name is incus.

Use the following commands to configure resolved:

resolvectl dns <network_bridge> <dns_address>
resolvectl domain <network_bridge> ~<dns_domain>

Note

When configuring resolved with the DNS domain name, you should prefix the name with ~. The ~ tells resolved to use the respective name server to look up only this domain.

Depending on which shell you use, you might need to include the DNS domain in quotes to prevent the ~ from being expanded.

DNSSEC and DNS over TLS

The incus DNS server does not support DNSSEC or DNS over TLS.

Depending on your resolved configuration the configuration will fail as the server does not support DNSSEC or DNS over TLS.

To disable both only for the bridge, use the following commands:

resolvectl dnssec <network_bridge> off
resolvectl dnsovertls <network_bridge> off

For example:

resolvectl dns incusbr0 192.0.2.10
resolvectl domain incusbr0 '~incus'
resolvectl dnssec incusbr0 off
resolvectl dnsovertls incusbr0 off

Note

Alternatively, you can use the systemd-resolve command. This command has been deprecated in newer releases of systemd, but it is still provided for backwards compatibility.

systemd-resolve --interface <network_bridge> --set-domain ~<dns_domain> --set-dns <dns_address> --set-dnsovertls=off --set-dnssec=off

The resolved configuration persists as long as the bridge exists. You must repeat the commands after each reboot and after Incus is restarted, or make it persistent as described below.

Make the resolved configuration persistent

You can automate the systemd-resolved DNS configuration, so that it is applied on system start and takes effect when Incus creates the network interface.

To do so, create a systemd unit file named /etc/systemd/system/incus-dns-<network_bridge>.service with the following content:

[Unit]
Description=Incus per-link DNS configuration for <network_bridge>
BindsTo=sys-subsystem-net-devices-<network_bridge>.device
After=sys-subsystem-net-devices-<network_bridge>.device

[Service]
Type=oneshot
ExecStart=/usr/bin/resolvectl dns <network_bridge> <dns_address>
ExecStart=/usr/bin/resolvectl domain <network_bridge> ~<dns_domain>
ExecStart=/usr/bin/resolvectl dnssec <network_bridge> off
ExecStart=/usr/bin/resolvectl dnsovertls <network_bridge> off
ExecStopPost=/usr/bin/resolvectl revert <network_bridge>
RemainAfterExit=yes

[Install]
WantedBy=sys-subsystem-net-devices-<network_bridge>.device

Replace <network_bridge> in the file name and content with the name of your bridge (for example, incusbr0). Also replace <dns_address> and <dns_domain> as described in Configure resolved.

Then enable and start the service with the following commands:

sudo systemctl daemon-reload
sudo systemctl enable --now incus-dns-<network_bridge>

If the respective bridge already exists (because Incus is already running), you can use the following command to check that the new service has started:

sudo systemctl status incus-dns-<network_bridge>.service

You should see output similar to the following:

user@host:~$ sudo systemctl status incus-dns-incusbr0.service

● incus-dns-incusbr0.service - Incus per-link DNS configuration for incusbr0     Loaded: loaded (/etc/systemd/system/incus-dns-incusbr0.service; enabled; vendor preset: enabled)     Active: inactive (dead) since Mon 2021-06-14 17:03:12 BST; 1min 2s ago    Process: 9433 ExecStart=/usr/bin/resolvectl dns incusbr0 n.n.n.n (code=exited, status=0/SUCCESS)    Process: 9434 ExecStart=/usr/bin/resolvectl domain incusbr0 ~incus (code=exited, status=0/SUCCESS)   Main PID: 9434 (code=exited, status=0/SUCCESS)

To check that resolved has applied the settings, use resolvectl status <network_bridge>:

user@host:~$ resolvectl status incusbr0

Link 6 (incusbr0)      Current Scopes: DNSDefaultRoute setting: no       LLMNR setting: yesMulticastDNS setting: no  DNSOverTLS setting: no      DNSSEC setting: no    DNSSEC supported: no  Current DNS Server: n.n.n.n         DNS Servers: n.n.n.n          DNS Domain: ~incus