Quoting Steve Litt (slitt@???):

> In daemontools-inspired inits, you express dependencies via if
> statements in the run script. The best way I've found, so far, to do
> this in Devuan is to use the following script, called netup.sh:

It's pretty nice. I note without objection that success depends not
only on port 80/tcp network connectivity but also on DNS resolution via
the system resolver routine. If you wished, you could test those two
things individually, e.g., if you wanted to issue/log diagnostic output.