Great guide. Just wanted to point out that Alpine busybox-extras package has inetd. For example, on Home Assistant Operating System (hassos):
[core-ssh ~]$ apk add busybox-extras
fetch https://dl-cdn.alpinelinux.org/alpine/v3.14/main/x86_64/APKINDEX.tar.gz
fetch https://dl-cdn.alpinelinux.org/alpine/v3.14/community/x86_64/APKINDEX.tar.gz
(1/1) Installing busybox-extras (1.33.1-r7)
Executing busybox-extras-1.33.1-r7.post-install
Executing busybox-1.33.1-r6.trigger
OK: 90 MiB in 100 packages
[core-ssh ~]$ which inetd
/usr/sbin/inetd
Then it’s only a matter of creating /etc/inetd.conf and setting it up as per the official documentation: Monitoring Linux in legacy mode. Might be easier for some compared to socat.
More on inetd configuration on Alpine: Alpine inetd setup | Alpine Linux forums