Reverse Proxy container and Web containers are running inside a container.
Using lavalink container as example.
root@nginx-proxy:/# dig a lavalink.lxd
; <<>> DiG 9.11.3-1ubuntu1.11-Ubuntu <<>> a lavalink.lxd
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 48956
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 65494
;; QUESTION SECTION:
;lavalink.lxd. IN A;; ANSWER SECTION:
lavalink.lxd. 0 IN A 10.75.254.49;; Query time: 0 msec
;; SERVER: 127.0.0.53#53(127.0.0.53)
;; WHEN: Mon May 18 16:32:23 CEST 2020
;; MSG SIZE rcvd: 57
root@nginx-proxy:/# dig aaaa lavalink.lxd
; <<>> DiG 9.11.3-1ubuntu1.11-Ubuntu <<>> aaaa lavalink.lxd
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 49179
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 65494
;; QUESTION SECTION:
;lavalink.lxd. IN AAAA;; ANSWER SECTION:
lavalink.lxd. 0 IN AAAA fd42:903d:d968:c9b3:216:3eff:fef0:3eb0;; Query time: 0 msec
;; SERVER: 127.0.0.53#53(127.0.0.53)
;; WHEN: Mon May 18 16:33:20 CEST 2020
;; MSG SIZE rcvd: 69
root@nginx-proxy:/# ping lavalink.lxd
PING lavalink.lxd(lavalink.lxd (fd42:903d:d968:c9b3:216:3eff:fef0:3eb0)) 56 data bytes
64 bytes from lavalink.lxd (fd42:903d:d968:c9b3:216:3eff:fef0:3eb0): icmp_seq=1 ttl=64 time=0.544 ms
64 bytes from lavalink.lxd (fd42:903d:d968:c9b3:216:3eff:fef0:3eb0): icmp_seq=2 ttl=64 time=0.086 ms
64 bytes from lavalink.lxd (fd42:903d:d968:c9b3:216:3eff:fef0:3eb0): icmp_seq=3 ttl=64 time=0.078 ms
64 bytes from lavalink.lxd (fd42:903d:d968:c9b3:216:3eff:fef0:3eb0): icmp_seq=4 ttl=64 time=0.097 ms
64 bytes from lavalink.lxd (fd42:903d:d968:c9b3:216:3eff:fef0:3eb0): icmp_seq=5 ttl=64 time=0.089 ms
Unable to run these outside the container (on the main host), as no name / service is known. I would assume then that lxd doesn’t add the hosts of the containers on the main system.