Event routing and messaging: how one service tells the next
Something happened. A file landed, a job finished, a customer clicked. A router takes that fact and delivers it to whoever asked to hear about it, without the sender knowing who that is.
What is event routing?
The alternative is each service calling the next one directly, which works until there are six of them and the fourth is down. A router sits in between: the sender publishes a fact and walks away, and anybody who cares subscribes. Adding a seventh consumer then changes nothing about the sender.
Two jobs usually get mixed up here. A bus routes events by their content to whoever is interested. A queue holds work for one consumer to pick up at its own pace, which is what protects an expensive step from a burst of traffic. Most real systems use both, and the clouds sell them as separate products.
Four ways to run it
Each cloud has a bus and a queue, sold separately. The open option is a log you run yourself and keep for as long as you like.
Amazon EventBridge[1]
The bus on AWS. Rules match on the content of an event and send it onward, including to a schedule or to another account. Amazon SQS is the queue beside it when a burst needs absorbing.
Official documentation →Azure Event Grid[2]
The same idea on Azure, built around the CloudEvents standard, with Azure Service Bus as the queue for work that must not be lost or must arrive in order.
Official documentation →Eventarc[3]
Routes events from Google Cloud services and your own publishers to Cloud Run and workflows, also on CloudEvents. Pub/Sub sits underneath as the queue and the fan-out.
Official documentation →Apache Kafka[4]
Not a bus but a durable log: events stay for a set time and a consumer can rewind and read them again. That is the reason to choose it, and also the reason it is more to operate.
Project documentation →Where I used it
The video pipeline
EventBridge carries the facts between the steps: a file arrived, labels are ready, a render finished. Because the steps only publish and subscribe, a new step can be added without touching the ones already running.
Read the write-up →Managed and self-hosted together: hybrid
An event usually carries less than the thing it is about, and that is the lever. Publish the fact and a reference, not the content: that a document arrived and where it is, not what it says. The bus can then sit in the cloud while the documents never leave, and a consumer inside your network is the only thing that resolves the reference.
What would help you next?
Learn to decide
The course “From Managed to Hybrid” teaches where AI should run: what each layer costs, what you operate and where your data has to stay. It is in preparation, with a free live session first.
Linda MohamedAI and cloud consultant, AWS Community Hero, Vienna
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Read more on ai-solutions.wiki
My open knowledge base, with longer comparisons, pricing notes and sources.
Sources
- Amazon EventBridge documentation. https://docs.aws.amazon.com/eventbridge/latest/userguide/eb-what-is.html
- Azure Event Grid documentation. https://learn.microsoft.com/en-us/azure/event-grid/overview
- Google Eventarc documentation. https://cloud.google.com/eventarc/docs/overview
- Apache Kafka documentation. https://kafka.apache.org/documentation/
- Amazon EventBridge, ai-solutions.wiki. https://ai-solutions.wiki/tools/amazon-eventbridge/
- Apache Kafka, ai-solutions.wiki. https://ai-solutions.wiki/tools/apache-kafka/
- Event-driven architecture, ai-solutions.wiki. https://ai-solutions.wiki/glossary/event-driven-architecture/
Links checked October 2026. Product names and features change: check the linked pages before you decide.
