EventArc: The state of eventing in Google Cloud

When defining event-driven architectures, it’s always good to keep up with how the landscape is changing. How do you connect microservices in your architecture? Is Pub/Sub the end-game for all events? To dive a bit deeper, let’s talk through the benefits of having a single orchestrator, or perhaps a choreographer is better?

Orchestration versus choreography refresher

My colleague @jeffreyaven did a recent post explaining this concept in simple terms, which is worth reviewing, see:

Should there really be a central orchestrator controlling all interactions between services…..or, should each service work independently and only interact through events?

  • Orchestration is usually viewed as a domain-wide central service that defines the flow and control of communication between services. In this paradigm, in becomes easier to change and ultimately monitor policies across your org.
  • Choreography has each service registering and emitting events as they need to. It doesn’t direct or define the flow of communication, but using this method usually has a central broker passing around messages and allows services to be truly independent.

Enter Workflows, which is suited for centrally orchestrated services. Not only Google Cloud service such as Cloud Functions and Cloud Run, but also external services.

How about choreography? Pub/Sub and Eventarc are both suited for this. We all know and love Pub/Sub, but how do I use EventArc?

What is Eventarc?

Announced in October-2020, it was introduced as eventing functionality that enables you, the developer, to send events to Cloud Run from more than 60 Google Cloud sources.

But how does it work?

Eventing is done by reading those sweet sweet Audit Logs, from various sources, and sending them to Cloud Run services as events in Cloud Events format. Quick primer on Cloud Events: its a specification for describing event data in a common way. The specification is now under the Cloud Native Computing Foundation. Hooray! It can also read events from Pub/Sub topics for custom applications. Here’s a diagram I graciously ripped from Google Cloud Blog:


Why do I need Eventarc? I have the Pub/Sub

Good question. Eventarc provides and 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. Actually, any service that has Audit Log integration can be an event source for Eventarc. Beyond easy integration, it provides consistency and structure to how events are generated, routed and consumed. Things like:


They specify routing rules from events sources, to event sinks. Listen for new object creation in GCS and route that event to a service in Cloud Run by creating an Audit-Log-Trigger. Create triggers that also listen to Pub/Sub. Then list all triggers in one, central place in Eventarc:

gcloud beta eventarc triggers list

Consistency with eventing format and libraries

Using the CloudEvent-compliant specification will allow for event data in a common way, increasing the movement towards the goal of consistency, accessibility and portability. Makes it easier for different languages to read the event and Google Events Libraries to parse fields.

This means that the long-term vision of Eventarc to be the hub of events, enabling a unified eventing story for Google Cloud and beyond.

Eventarc producers and consumers

In the future, you can excpect to forego Audit Log and read these events directly and send these out to even more sinks within GCP and any HTTP target.

This article written on inspiration from https://cloud.google.com/blog/topics/developers-practitioners/eventarc-unified-eventing-experience-google-cloud. Thanks Mete Atamel!

Microservices Concepts: Orchestration versus Choreography

One of the foundational concepts in microservices architecture and design patterns is the concept of Orchestration versus Choreography. Before we look at a reference implementation of each of these patterns, it is worthwhile starting with an analogy.

This is often likened to a Jazz band versus a Symphony Orchestra.

A modern symphony orchestra is normally comprised of sections such as strings, brass, woodwind and percussion sections. The sections are orchestrated by a conductor, usually placed at a central point with respect to each of the sections. The conductor instructs each section to perform their components of the overall symphony.

By contrast, a Jazz band does not have a conductor and also features improvisation, with different musicians improvising based upon each other. Choreography, although more aligned to dance, can involve improvisation. In both cases there is still an intended output and a general framework as to how the composition will be executed, however unlike a symphony orchestra there is a degree of spontaneity.

Now back to technology and microservices…

In the Orchestration model, there is a central orchestration service which controls the interactions between other services, in other words the flow and control of communication and/or message passing between services is controlled by an orchestrator (much like the conductor in a symphony orchestra). On the plus side, this model enables easier monitoring and policy enforcement across the system. A generalisation of the Orchestration model is shown below:

Orchestration model

By contrast, in the Choreography model, each service works independently and interacts with other services through events. In this model each service registers and emits events as they need to. The flow (of communication between services) is not predefined, much like a Jazz band. This model often includes a central broker for message passing between services, but the services operate independently of each other and are not controlled by a central service (an orchestrator). A generalisation of the Choreography model is shown below:

Choreography model

We will post subsequent articles with implementations of these patterns, but it is worthwhile getting a foundational understanding first.

Using the Azure CLI to Create an API using a Function App within API Management

Function Apps, Logic Apps and App Services can be used to expose APIs within Azure API Management which is an easy way to deploy serverless microservices. You can see this capability in the Azure portal below within API Management:

Add a new API using a Function App as a back end

Like most readers, I like to script everything, so I was initially frustrated when I couldn’t replicate this operation in the Azure cli, REST, PowerShell, or any of the other SDKs or IaC tools. Others shared my frustration as seen here.

I was nearly resigned to using click ops in the portal (arrrgh) before I worked out this workaround.

The Solution

There is a bit more prep work required to automate this process, but it is well worth it.

1. Create an OpenApi (or Swagger spec or WADL) specification document, as seen below (use the absolute URL for your Function App in the url parameter):

2. Use the az apim api import function (not the az apim api create function), as shown here:

3. Associate the API with a product (which is how you can rate limit APIs)

That’s it! You can now access your function via the API gateway using the gateway url or via the developer portal as seen below:

Function App API in API Management in the Azure Portal
Function App API in the Dev Portal