A simple (?) audience interactivity solution intended for custom-developed overlays to full-screen presentations. This is an evolution of something I've been doing in my own presentations for a long time, but more flexible and stable than what I'd built previously.

• The big screen presentation at web/big/. One of my goals here was to have zero UI dependencies, and I achieved that pretty easily. All the frontends use the Paho MQTT client (32K), loaded via CDN.

• The audience app at web/. This app prompts users with questions. Also zero UI dependencies. The index.html gets generated via index-src.html using Parcel.

• The speaker app at web/admin/. It controls everything else as an authenticated admin user.

• An nginx web server for static assets, and reverse proxy for WebSocket/MQTT.

• Node-RED, which contain all the (minimal) backend logic for messages and message routing.

• A Mosquitto server, which connects all clients and NODE-RED.

To get things running, you need to install nginx, Mosquitto, yarn, NodeJS, and Node-RED. Do an npm install in the server dir. And really, that's all. Update the start.sh script and nginx.conf with your local paths and (un)comment the appropriate Linux/Mac config to get rolling.

The admin app prompts for a password, which needs to match the adminapp Mosquitto password, which you need to set using mosquitto_passwd. You also need to make sure the passwords match for the adminred user — setting it via the Mosquitto pwfile and also in the node-red flows. When deploying, change the password in Node-RED (the config is shared between nodes) and then via mosquitto_passwd servers/mosquitto.pwfile USERNAME for adminred, adminapp, and big; then match the passwords to web/admin/index.js and web/big/index.html.

There are a bunch of tests at web/admin/test.html. Also, all vanilla JS.

From that point, everything is driven via the presentation "script" in web/admin/script.js. The admin app sends events over WebSocket to Mosquitto, and from there they get routed to audience and big screen.

Each .html file has a toggle for ssl. Use yarn parcel src/index.html to serve a build, and:

yarn parcel build --dist-dir web/ src/index.html

to build to web/index.html. The other apps (big/ and admin/) aren't built, and don't need to be.

It's easier to troubleshoot with MQTT if you listen for events:

`% mosquitto_sub -u adminred -P PASSWORD -t "user/in"`
`% mosquitto_sub -u adminred -P PASSWORD -t "user/out/+"`
`% mosquitto_sub -t "\$SYS/broker/clients/connected"`
`% mosquitto_sub -u adminred -P PASSWORD -t "admin/state"`

• Mosquitto is configured to limit to a single connection per authenticated (or identified) users. You can't have the admin app open on multiple devices without creating a tug of war of disconnects and reconnects. Be aware, since the app reconnects automatically!

• You need high file limits set on a Linux server to scale to thousands of users via mosquitto. Most systems I've encountered limit at 1024 by default.

• There is little enforcement here; any user can delete their ID from localStorage and have a new session. This is intentional, to allow for broad anonymous access. This obviously wouldn't be accepetable for anything long-lived, and there is bound to be hack potential.

• I'm not entirely clear how Node-RED stores the MQTT server credentials, but I've found it periodically necessary to resupply Node-RED the mosquitto credentials after a restart. If things aren't working, re-login using one of the MQTT nodes in the flow.