Access LXC containers by name

By default, for every managed network bridge, LXD sets dnsmasq as DNS and DHCP server. The containers with addresses assigned by dnsmasq can access each other by name using the default domain name lxd.

To access the LXC containers from a host running systemd-resolved, the resolved service must be configured. The configuration is not persistent between reboots and restarts of LXD but can be made persistent. A relevant link is at the end of this document.

Settings for network bridge

For a bridge network the domain advertised to DHCP client and used for DNS resolution is, by default, lxd.

If you create a new network the domain can be specified by using the dns.domain configuration option. Here is an example:

lxc network create testDNSnet --type=bridge \
    ipv4.address='10.11.12.1/24' \
    ipv4.dhcp.ranges='10.11.12.64-10.11.12.127' \
    ipv4.nat=true \
    ipv6.address=none \
    dns.domain='abc'

For an existing network the domain can be set using:

lxc network set testDNSnet dns.domain='abc'

Configuration for resolved service

sudo resolvectl dns testDNSnet 10.11.12.1
sudo resolvectl domain testDNSnet '~abc'

Note:~ in front of the domain name informs the resolved service to redirect the queries for that domain only to the specified DNS server.

Profile for containers

This profile attaches the container’s eth0 network card to the testDNS network bridge.

lxc profile create testDNS
lxc profile device add testDNS eth0 nic \
    name=eth0 nictype=bridged \
    parent=testDNSnet

Containers with dynamic IP addresses

Launch a container with IP addresse assigned by DHCP:

lxc launch ubuntu-minimal:22.04 testD \
    --profile default --profile testDNS

Containers with static IP addresses

# create a profile with a static IP configuration
lxc profile create ip7
cat << EOF | lxc profile set ip7 cloud-init.network-config -
version: 1
config:
  - type: physical
    name: eth0
    subnets:
      - type: static
        ipv4: true
        address: 10.11.12.7
        netmask: 255.255.255.0
        gateway: 10.11.12.1
        control: auto
  - type: nameserver
    address: 10.11.12.1
EOF

# add the host record to dnsmasq
lxc network set testDNSnet raw.dnsmasq \
    host-record=testS.abc,10.11.12.7

# launch a container with previously created profile
lxc launch ubuntu-minimal:22.04 testS \
    --profile default --profile testDNS --profile ip7

Test

host testD.abc
host testS.abc
lxc exec testD -- resolvectl query testS.abc
lxc exec testS -- resolvectl query testD.abc

Cleanup

lxc delete testD --force
lxc delete testS --force
lxc profile delete ip7
lxc profile delete testDNS
lxc network delete testDNSnet

The configuration of resolved service is automatically deleted when the bridge network is deleted.

Persistency

To make the notification persistent see Make the resolved configuration persistent in How to integrate with systemd-resolved