Oh. You got it backward.
volumes:
- volume:
host: /var/discourse/shared/standalone
guest: /shared
- volume:
host: /var/discourse/shared/standalone/log/var-log
guest: /var/log
So you want to add
- volume:
host: /forum_images
guest: /shared/uploads
Then you can
./launcher destroy app;./launcher start app
Then you can
./launcher enter app
ls /shared/uploads
to see if the stuff is there