In the MQTT world, in which Pub/Sub is based, every publisher is a client, and every subscriber is a client. You can be both, too!

Assuming your existing backend is in $SOME_CLOUD_PROVIDER, publishing messages to Pub/Sub is just a few lines of code in your favorite language - we have a couple of examples up in JS + Rust - e.g. https://developers.cloudflare.com/pub-sub/examples/connect-j...

Subscribers receiving those messages can be anywhere you can run an MQTT client, which turns out to be... a lot of places :-)

(I'm the PM for this, and we'll be adding more examples to our docs in the coming weeks)