I've found that the easiest way to tell a user that the site is undergoing maintenance is
to show them the maintenance page that lives in a separate repository ereadingtool/maintenance. To do this, hop onto the node_frontend container with docker exec -it node_frontend /bin/bash. Make a directory /var/www/maintenance/html and place the following files in it:
.
|-- dist
| `-- elm.compiled.js
|-- img
| `-- engineering_black.svg
|-- index.html
`-- main.js
Then create a configuration file at /etc/nginx/sites-available/maintenance by cping /etc/nginx/sites-available/<SITE>.<TLD>. Change line 8 of this file to root /var/www/maintenance/html;. Head over to /etc/nginx/site-enabled and create the symbolic link to /etc/nginx/sites-available
ln -s /etc/nginx/sites-available/maintenance /etc/nginx/sites-enabled/
being sure to delete the other enabled symbolic link. Reload the page with
service nginx reload
There should now be a maintenance page.