Cloud Pub/Sub in Action - ep. 3

An order service publishes an “order received” message that both packaging and notification need to process. This console-and-Python walkthrough gives each consumer its own Pub/Sub subscription, then shows why one consumer can start late without missing its message.

Key points

• The topology gives each consumer a subscription: The order publisher writes to one topic, while packaging and notification each receive through their own pull subscription 00:00–02:09(opens in a new tab).
• The 2019 demo shares one identity across three processes: It grants publisher and subscriber roles to one service account and uses a downloaded JSON key for the local Python samples. This is historical demo setup, not a recommendation to share long-lived credentials in a deployment 02:09–05:20(opens in a new tab).
• Acknowledgement advances one subscription's state: When packaging acknowledges the message, Pub/Sub removes it from the packaging backlog, not from the notification subscription 05:20–06:23(opens in a new tab).
• A late subscriber still receives its own copy: Notification starts after publication but receives the message already retained for its subscription 05:20–06:23(opens in a new tab).

Full video: https://www.youtube.com/watch?v=f5DOsB7Nlw0(opens in a new tab)