There are already other ways to get events to Cloud Run, so you might wonder what’s special about Eventarc? I’ll get to this question, but let’s first explore one of those ways, Pub/Sub.
As shown in this Using Pub/Sub with Cloud Run tutorial, Cloud Run services can receive messages pushed from a Pub/Sub topic. This works if the event source can directly publish messages to a Pub/Sub topic. It can also work for services that have integration with Pub/Sub and publish their events through that integration. For example, Cloud Storage is one of those services and in this tutorial, I show how to receive updates from a Cloud Storage bucket using a Pub/Sub topic in the middle.
For other services with no integration to Pub/Sub, you have to either integrate them with Pub/Sub and configure Pub/Sub to route messages to Cloud Run or you need to find another way of sourcing those events. It’s possible but definitely not trivial. That’s where Eventarc comes into play.
Eventarc provides an easier path to receive events not only from Pub/Sub topics but from a number of Google Cloud sources with its Audit Log and Pub/Sub integration. Any service with Audit Log integration or any application that can send a message to a Pub/Sub topic can be event sources for Eventarc. You don’t have to worry about the underlying infrastructure with Eventarc. It is a managed service with no clusters to set up or maintain.
It also has some concrete benefits beyond the easy integration. It provides consistency and structure to how events are generated, routed, and consumed. Let’s explore those benefits next.
Eventarc introduces the notion of a trigger. A trigger specifies routing rules from event sources to event sinks. For example, one can listen for new object creation events in Cloud Storage and route them to a Cloud Run service by simply creating an Audit Log trigger as follows: