Just to follow up, some things have changed since this thread’s last activity:
@sseemayer’s plugin has become official and moved to https://github.com/dokku/dokku-letsencrypt, and it’s wonderful. I’m using it with great success currently. It’s so nice to just type
dokku letsencrypt my-app and it’s done.
Also Dokku moved to its own github org.
I found this thread searching “dokku” here to see if anyone had renewal via cron working with the dokku plugin, but I’ll ask about that in a separate thread. Just wanted to stop and say thanks for the plugin and help others find it. Using Let’s Encrypt with Dokku is now a dream.