is it possible listen to a pub/sub topic without a subscription?

[Nick Pomfret]

I'm wondering if it's possible to broadcast messages on a topic and have a process listen to them but without a subscription?

The reason is that I don't care about losing messages if say my application was switched off.  And when it's switched back on I only want to receive message published since the moment it was switched on.

[Julie (cloud platform support)]

According to this Pub/Sub FAQ question trying to publish a topic without subscriptions will result in the messages being dropped, however the publish operation should succeed which you can use to confirm that your application is switched on. 

[Nick Pomfret]

I'm not sure I understand your answer.

Maybe my question was unclear...  I am publishing messages onto  a topic.  If my app isn't running I'm happy for those messages to disappear. AND I don't want a backlog of messages when I switch my app on.  I want topic behaviour, not queue behaviour (which is what I'm getting when I create a subscriber).

On Mon, 29 Oct 2018 at 18:12, 'Julie (cloud platform support)' via Google App Engine <google-a...@googlegroups.com> wrote:

According to this Pub/Sub FAQ question trying to publish a topic without subscriptions will result in the messages being dropped, however the publish operation should succeed which you can use to confirm that your application is switched on. 

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[Olu]

By design, for every subscription the Google Cloud PubSub delivers messages at least once. Hence, even if the subscriber is not present, the unacknowledged messages are stored in a persistent storage for 7 days after the messages are published. 

The documentation explains the exceptions to the "at least once delivery" approach of the Cloud PubSub and why a message would be deleted. Messages published before a subscription is created would not be retrievable. Also, a maximum retention of 7 days, after which the message would be deleted.

Hence, it is intended behavior that your Subscriber would still be able to retrieve backlogs of messages (that are under 7 days), even if it was off for some time.

[Olu]

If you want a feature that offers a different behavior on Cloud PubSub, I recommend reporting this Feature Request on the Issue tracker. The Feature request would be submitted to the PubSub Engineers. However, Feature Requests are subject to evaluations and there are usually no ETA for the implementation.