Thanks for your help, @bversluijs!
I have an intriguing observation. I can ping [mydomain].org, but pinging api.[mydomain].org gives me:
$ ping api.[mydomain].org
cannot resolve api.[mydomain].org: Unknown host
$ curl api.[mydomain].org
curl: (6) Could not resolve host: api.[mydomain].org
At the same time, running docker ps shows me that the necessary containers are apparently running:
root@openbalena:~# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
b993d71af1be openbalena_haproxy "/docker-entrypoint.…" 16 hours ago Up 16 hours 0.0.0.0:80->80/tcp, 0.0.0.0:443->443/tcp, 222/tcp, 5432/tcp, 0.0.0.0:3128->3128/tcp, 6379/tcp openbalena_haproxy_1
11c8330cfdd2 balena/open-balena-vpn:v8.10.0 "/usr/bin/entry.sh" 16 hours ago Up 16 hours 80/tcp, 443/tcp, 3128/tcp openbalena_vpn_1
41c0dfae76a3 balena/open-balena-api:v0.19.5 "/usr/bin/entry.sh" 16 hours ago Up 16 hours 80/tcp openbalena_api_1
219929aec5de balena/open-balena-registry:v2.11.1 "/usr/bin/entry.sh" 16 hours ago Up 16 hours 80/tcp openbalena_registry_1
d6518d97720f balena/open-balena-s3:v2.8.5 "/usr/bin/entry.sh" 16 hours ago Up 16 hours 80/tcp openbalena_s3_1
398a48e1fe5a redis:alpine "docker-entrypoint.s…" 16 hours ago Up 16 hours 6379/tcp openbalena_redis_1
1bd8dacab6b5 openbalena_cert-provider "/entry.sh /usr/src/…" 16 hours ago Up 16 hours 80/tcp openbalena_cert-provider_1
e30ae561b38d balena/open-balena-db:v2.0.3 "docker-entrypoint.s…" 16 hours ago Up 16 hours 5432/tcp openbalena_db_1
Also thanks for responding, @JuanFRidano!
Running the dig commands shows me that I do have an ;; ANSWER SECTION: on both [mydomain].org and api.[mydomain].org. I think the CNAME records are correct, though to troubleshoot, here is the output:
$ dig [mydomain].org
; <<>> DiG 9.9.7-P3 <<>>[mydomain].org
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 19807
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;[mydomain].org. IN A
;; ANSWER SECTION:
[mydomain].org. 15 IN A [CORRECT IP ADDRESS HERE]
;; Query time: 11 msec
;; SERVER: 192.168.2.1#53(192.168.2.1)
;; WHEN: Fri Jun 12 23:23:08 EDT 2020
;; MSG SIZE rcvd: 64
$ dig api.[mydomain].org
; <<>> DiG 9.9.7-P3 <<>> api.[mydomain].org
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 28202
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;api.[mydomain].org. IN A
;; ANSWER SECTION:
api.[mydomain].org. 15 IN CNAME api.[mydomain].org.
;; Query time: 226 msec
;; SERVER: 192.168.2.1#53(192.168.2.1)
;; WHEN: Fri Jun 12 23:25:06 EDT 2020
;; MSG SIZE rcvd: 66
Could it be I need to open up some ports or configure NGINX?