How to enable hostname resolution (dns) for lxd containers from the lxd host?

Question

How to enable lxd hostname resolution from the lxd host?

After creating the below container:

>>> lxc launch ubuntu: container
Creating container
Starting container

>>> lxc list
+-----------------+---------+----------------------+------+------------+-----------+
| container       | RUNNING | 10.240.38.157 (eth0) |      | PERSISTENT | 0         |
+-----------------+---------+----------------------+------+------------+-----------+

It can be reached using the IP address but not using the hostname:

>>> ping 10.240.38.157 -c 3
PING 10.240.38.157 (10.240.38.157) 56(84) bytes of data.
64 bytes from 10.240.38.157: icmp_seq=1 ttl=64 time=0.082 ms
64 bytes from 10.240.38.157: icmp_seq=2 ttl=64 time=0.053 ms
64 bytes from 10.240.38.157: icmp_seq=3 ttl=64 time=0.041 ms

--- 10.240.38.157 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2044ms
rtt min/avg/max/mdev = 0.041/0.058/0.082/0.019 ms

>>> ping container
ping: unknown host container

How to enable the lxd containers to be reached by hostname from the lxd host?

Answer 1

LXD sets up for you a DHCP & DNS server (dnsmasq) that only listens on the lxdbr0 interface. That's the DHCP server that lets containers have hostnames like c1.lxd, mycontainer.lxd and so on. And it works only within the containers, because the containers are autoconfigured with that LXD's DNS server.

If you want the host to understand those c1.lxd, mycontainer.lxd hostnames, you need to configure your host's DNS client service to also consult LXD's DNS server.

Answer 2

This is an easy way to temporarily add the LXD DNS server to your host machine.

First, add the DNS server of lxdbr0.

sudo resolvectl dns lxdbr0 $(ip -f inet addr show lxdbr0 | sed -En -e 's/.*inet ([0-9.]+).*/\1/p')

Second, make sure all requests to *.lxd are sent to that DNS server.

sudo resolvectl domain lxdbr0 lxd

After this, any requests to containername.lxd will be resolved to the container IP address. Make sure to add .lxd to the hostname.

Note that this config will be forgotten after a reboot.