Events have become an essential piece of modern reactive systems. Indeed, events can be used to communicate from one service to another, trigger out-of-band processing, or send a payload to a service like Kafka. The problem is that event publishers may express event messages in any number of different ways, regardless of content. For example, some messages are payloads in JSON format to serialize and deserialize messages by application. Other applications use binary formats such as Avro and Protobuf to transport payloads with metadata. This is an issue when building an event-driven architecture that aims to easily integrate external systems and reduce the complexity of message transmission.
CloudEvents is an open specification providing a common format to describe events and increase interoperability. Many cloud providers and middleware stacks, including Knative, Kogito, Debezium, and Quarkus have adopted this format after the release of CloudEvents 1.0. Furthermore, developers need to decouple relationships between event producers and consumers in serverless architectures. Knative Eventing is consistent with the CloudEvents specification, providing common formats for creating, parsing, sending, and receiving events in any programming language. Knative Eventing also enables developers to late-bind event sources and event consumers. For example, a cloud event using JSON might look like this: