- Is Pub/Sub significantly faster way of communicating between, say, Kubernetes Engine (GKE) api server and a Cloud Function (GCF)?
- Is it possible to use Pub/Sub to have such communication between GKE from one Google Cloud Project and GCF from another Google Cloud Project?
- What is the way to communicate with Cloud Functions from another Google Cloud Project with low latency?
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I think a global answer will clarify your questions. For this particular case, there are two ways to trigger a Google Cloud Function (GCF). You can directly make an HTTP request or you can subscribe the GCF to a topic by using Pub/Sub [https://cloud.google.com/functions/docs/calling ].
If your requests are occasional, an HTTP request will be faster because you don't need an intermediary. If that's not the case, then the Pub/Sub subscription queues the messages and ensures the delivery by retrying them until it receives confirmation.
To communicate between Google Kubernetes Engine (GKE) from one Google Cloud Project and Google Cloud Function (GCF) to another Google Cloud Project you can use either option. Trigger the GCF by the HTTP request directly or do it by publishing the message. When publishing, specify the project where you are sending it and the desirable topic in that project.
Also you need to give the proper permission to the service account to access from one project to the other:
For Pub/Sub https://cloud.google.com/pubsub/docs/authentication
For HTTP request https://cloud.google.com/solutions/authentication-in-http-cloud-functions.
- Google Cloud Function HTTP triggers documentation here: https://cloud.google.com/functions/docs/calling/http
- Pub/Sub documentation here: https://cloud.google.com/pubsub/docs/reference/libraries (you can access to GitHub by the links in the code and see functions examples for each language)
