Event-Driven Services in the Cloud: Azure Event Grid, AWS Event Bridge, and Google EventArc

I mentioned Azure Event Grid in a scenario with D365FO Business Events in a previous blog post. It is a Platform as a Service (PaaS) capability in Azure or eventing platform or event bus (I see various terms describing the service) allowing you to centrally manage events. In addition, it supports direct event filtering based on event type, prefix, or suffix, so your application will only receive events that are relevant to it.

Whether you want to handle built-in Azure events, such as a file being added to storage, or create your own custom events and event handlers, Event Grid supports both options via the same underlying model. Thus, regardless of the service or use case, intelligent routing and filtering capabilities apply to every event scenario and ensure that your apps focus on core business logic rather than worrying about event routing.

In this blog post, I like to dive into Azure Event Grid and competitive offering on the two other big cloud providers, AWS and Google.

Azure Event Grid

In 2017 Microsoft introduced Azure Event Grid as a fully-managed event routing service and the first of its kind (meaning the public cloud claimed it was the first offering the service). Dan Rosanova, previously Principal Program Manager Lead at Microsoft, now Director Program Management at Confluent, said in an InfoQ news item on the introduction:

Azure Event Grid fills a gap in the current cloud messaging space, not just in Azure but also across all cloud providers. We have services for messaging, queuing, and telemetry, but nothing for comprehensive eventing, particularly for cross-service or cross-cloud scenarios.

Within Azure service supporting Event Grid generates events routed to several event handlers. These handlers support event filtering and reliable delivery, ranging from Azure Functions to webhooks. Furthermore, underhood, the service relies on Service Fabric and thus can scale automatically to handle millions of events per second.

Event Grid model of sources and handlers

Source: https://docs.microsoft.com/en-us/azure/event-grid/overview

The Event Grid concept revolves around events emitted from a source (publisher), an Azure service, or a third-party source that adheres to the event schema (proprietary schema or the CNCF Cloud Events schema). For example, IoT Hub, Storage, and others are all event publishers in Azure. Following that, the events are sent to a topic in Event Grid, and each topic can have one or more subscribers (event handlers). A topic can be set up with the event publisher, or it can be a custom topic for custom events. Finally, event handlers respond to and process the events. Functions, WebHooks, and Event Hubs are examples of event handlers in Azure.

Azure Event Grid generally became available (GA) in February 2018 and Clemens Vasters, Principal Architect Messaging Services at Microsoft, said:

Event Grid is catching everyone’s attention because it unlocks new architectural possibilities for cloud platforms and applications: it’s the glue that enables information flow between services, and Event Grid allows expanding the capabilities of existing services by extension.

And that’s what also triggered or got the attention of AWS as they released EventBridge in July 2019, labeled as a serverless event bus that allows AWS services, Software-as-a-Service (SaaS), and custom applications to communicate with each other using events.

Since the GA, Azure EventGrid received several updates, including advanced filtering, retry policies, and support for CloudEvents. More details and samples are available on the Microsoft documentation and GitHub. Note that there is also an introductory paper available on Azure Event Grid and GitHub from Clemens.

AWS Eventbridge

You can use EventBridge to build and manage event-driven solutions by centrally controlling event ingestion, delivery, security, authorization, and error handling. Furthermore, you do not have to manage any infrastructure or scaling and only pay for the events that their applications consume, similar to Azure Event Grid. Moreover, the concepts are the same too.

How Amazon EventBridge connects applications using events

Source: https://aws.amazon.com/eventbridge/

However, Amazon Eventbridge surpasses Azure Event Grid with features (as you can see from the diagram above). It has a schema registry allowing you to discover, create, and manage OpenAPI schemas for events on EventBridge. According to the documentation, you can find schemas for existing AWS services, create and upload custom schemas, or generate a schema based on events located on an event bus. Furthermore, EventBridge enables you to generate and download code bindings for all event schemas to help quickly build applications that use those events.

Next to the schema registry, the service integrates easily with third-party services like Zendesk, Pagerduty, and SignalFx. Amazon has set up an extensive partner program for these integrations. Event Grid supports partner events (still preview) yet only has one with Auth0.  

Another capability Amazon EventBridge offers is event replay and archive –  allowing you to archive events so that you can easily replay them later by starting an event replay. Again, a capability that is not available in Azure Event Grid. Although it is something, you can find in Azure Event Hubs. You can configure the archive capability with the actions menu on the EventBridge Console and set the events’ retention period (ranging from zero days to infinite). Subsequently, you can optionally set a pattern matching filter for which events to archive. Later, when events run through the event bus, you can replay the events by selecting the appropriate archive.

Sample Implementation AWS EventBridge

Since the inception of Event Grid, I followed its evolution and wrote and presented on it. Moreover, I followed its competitive solution on AWS and, next to writing about it on InfoQ, built a simple demo around it using .NET in combination with AWS EventBridge. Below you will find a diagram of the demo I created.

Amazon EventBridge Demo

From .NET code, I send an event to a custom event bus containing a rule to send the event to a destination, an Amazon Simple Queue. Subsequently, an AWS Lambda function can poll the queue and receive the message – below shows the steps until the SQS queue.

EventBridge Demo Steps

You can find a live demo on YouTube with demoing the above (minute 19). Furthermore, you can look at other samples like in the AWS documentation or on GitHub.

Google Eventarc

With Azure and AWS offering a service to centrally manage events, Google followed in October 2020 with Eventarc to provide customers with a service to connect Cloud Run services with events from various sources, adhering to the CloudEvents standard. It became generally available in January 2021.

Eventarc’s underlying delivery mechanism is Pub/Sub, which includes topics and subscriptions similar to previously discussed Event Grid and EventBridge. Event sources create events and publish them in any format on the Pub/Sub topic. The events are then delivered to the Google Run sinks. For applications running on Cloud Run, you can use Eventarc to use a Cloud Storage event (via Cloud Audit Logs) to trigger a data processing pipeline or an event from custom sources (publishing to Cloud Pub/Sub) to signal between microservices.

Eventarc Overview

Source: https://codelabs.developers.google.com/codelabs/cloud-run-events#1

The diagram above shows what Google hopes to achieve with Eventarc. Currently, you can Cloud Run Service as a destination, and recently Cloud Run for Anthos has been added. Additionally, you can leverage a UI through the Google Cloud console allowing you to view, edit, and delete EventArc triggers. Lastly, you can find more details and samples on GitHub.

CloudEvents Schema

Before I end the blog post with some conclusions, I like to discuss the CloudEvent schema. CloudEvents is an open-source specification for consistently describing event data to make event declaration and delivery easier across services, platforms, and beyond. The Cloud Native Computing Foundation (CNCF) is the driving force behind the specification, which reached the version 1.0 milestone in October 2019.

Clemens Vasters, Principal Architect Messaging Services at Microsoft, stated in an InfoQ news item on CloudEvents:

The goal was to provide an industry definition and open framework for what an “event” is, what its minimal semantic elements are, and how events are encoded for transfer and how they are transferred and do so using the major encodings and application protocols in use today rather than inventing new ones.

Earlier I mentioned that Azure Event Grid has its own proprietary schema and supports CloudEvent schema. The differences are shown below:

CloudEvent vs Event Grid Schema

Note that Azure Event Grid and Google Eventarc support the CloudEvent schema; however, AWS EventBridge does not, leading to customization.


From this blog post, you can probably conclude that AWS with Eventbridge delivers the most complete event bus or eventing platform in the cloud than Event Grid and Eventarc. If I rank each, AWS comes first, Azure second, and Eventarc third based on features and maturity. The service overlap in concepts, yet implementation, support, and features differ dramatically. Interestingly, they all support changes in their respective storage service. Azure Event Grid brings support for events like when blobs are created, and EventBridge supports S3 notifications and Eventarc triggers for Cloud storage. You can think of various scenarios regarding storage and events, for instance, the pipe and filters pattern implementation discussed in my first blog post.