> the publisher is responsible for now maintaining arbitrary ordering IDs and passing this in the publish method

Ah, thanks for pointing this out. The "ordering ID" bit is actually a remnant of how to publish messages before we had officially ordering key support (and only shows up in Node, but not our other samples https://cloud.google.com/pubsub/docs/publisher#using_orderin...). We'll be fixing this sample shortly.

Disclaimer: I work on Cloud Pub/Sub. This explanation is my own.