Can I use Google Cloud Pub/Sub across different Google Cloud projects?

Question

Let's say I have project A, B and C in Google Cloud with several cloud functions in each one.

I want to setup a Pub/Sub in project C so the functions in A and B can subscribe to.

Is this possible? Do I need to setup some kind of service account with custom permissions?

Thanks

As far as I know the PubSub topic must be in the same project as the Cloud Functions that it triggers. But you could publish to that topic from other projects. — Frank van Puffelen
To send push notifications to functions in other projects I think its possible as it is a simple HTTP request from the Pub/Sub server. But to publish from other functions is something that I'm not sure about — martosoler
I cannot answer for Google Cloud Functions specifically, but I have a PubSub in one project that I access (both to publish and subscribe) from apps on Google Cloud Kubernetes Engine in a different project. GOOGLE_APPLICATION_CREDENTIALS simply has to point to the certificate of a service account with access to the PubSub in the correct project. — ZackK
@FrankvanPuffelen could you post your comment as an answer? Thank you. — komarkovich
I'm actually not sure I am correct. @ZackK seems to indicate that it is possible to call PubSub across projects, which is a better answer for what OP is asking. — Frank van Puffelen

Calle Engene Calle Engene · Accepted Answer · 2019-03-05T13:02:25

In the subscribing project on the IAM page, add a new member with the Pub/Sub Publisher role, the new member name is the serviceaccount-email of from the publishing project. Then create a cloud function in the publishing project and assign the same service-account in the bottom of the page(under more) to the function.

Here's a node example for a cloud function:

const PubSub = require('@google-cloud/pubsub');
const pubsub = new PubSub();
const topic = pubsub.topic('projects/subscribing-project-name/topics/topic-to- 
publish-to');
const publisher = topic.publisher();

exports.helloWorld = (req, res) => {
const customAttributes = {
message: 'Hello'
};
publisher.publish(Buffer.from("Hello from another project"), customAttributes, 
(err) => {
if (err) {
  res.status(500).send(JSON.stringify({ success: false, error: err.message }));
  return;
}
res.status(200).send(JSON.stringify({ success: true, message: "Message sent to 
pubsub topic" }));
});
};

Can I use Google Cloud Pub/Sub across different Google Cloud projects?

2 Answers