CloudEvents Integration

Introduction

CloudEvents is a specification for describing event data in common formats to provide interoperability across services, platforms and systems.

As of May 2021, EventMesh contains the following major components: eventmesh-runtime, eventmesh-sdk-java and eventmesh-connector-rocketmq. For a customer to use EventMesh, eventmesh-runtime can be deployed as microservices to transmit customer's events between event producers and consumers. Customer's applications can then interact with eventmesh-runtime using eventmesh-sdk-java to publish/subscribe for events on given topics.

CloudEvents support has been a highly desired feature by EventMesh users. There are many reasons for users to prefer using a SDK with CloudEvents support:

• CloudEvents is a more widely accepted and supported way to describe events. eventmesh-sdk-java currently uses the LiteMessage structure to describe events, which is less standardized.
• CloudEvents's Java SDK has a wider range of distribution methods. For example, EventMesh users currently need to use the SDK tarball or build from source for every EventMesh release. With CloudEvents support, it's easier for users to take a dependency on EventMesh's SDK using CloudEvents's public distributions (e.g. through a Maven configuration).
• CloudEvents's SDK supports multiple languages. Although EventMesh currently only supports a Java SDK, in future if more languages need to be supported, the extensions can be easier with experience on binding Java SDK with CloudEvents.

Requirements

Functional Requirements

Requirement ID	Requirement Description	Comments
F-1	EventMesh users should be able to depend on a public SDK to publish/subscribe events in CloudEvents format	Functionality
F-2	EventMesh users should continue to have access to existing EventMesh client features (e.g. load balancing) with an SDK that supports CloudEvent	Feature Parity
F-3	EventMesh developers should be able to sync eventmesh-sdk-java and an SDK with CloudEvents support without much effort/pain	Maintainability
F-4	EventMesh support pluggable protocols for developers integrate other protocols (e.g. CloudEvents\EventMesh Message\OpenMessage\MQTT ...)	Functionality
F-5	EventMesh support the unified api for publish/subscribe events to/from event store	Functionality

Performance Requirements

Requirement ID	Requirement Description	Comments
P-1	Client side latency for SDK with CloudEvents support should be similar to current SDK

Design Details

Binding with the CloudEvents Java SDK (similar to what Kafka already did, see Reference for more details) should be an easy way to achieve the requirements.

Pluggable Protocols

Process of CloudEvents under EventMesh

For TCP

SDK side for publish

• add the CloudEvents identifier in package header
• use CloudEventBuilder build the CloudEvent and put it into the package body

SDK side for subscribe

• add convert function under the ReceiveMsgHook interface, for converting the package body to the specific protocol with the identifier in package header
• different protocols should implement the ReceiveMsgHook interface

Server side for publish

• design the protocol convert api contains decodeMessage interface which convert the package's body to CloudEvent
• update Session.upstreamMsg() in MessageTransferTask change the input parameter Message to CloudEvent, the CloudEvent use the last step decodeMessage api convert
• update SessionSender.send() change the input parameter Message to CloudEvent
• update MeshMQProducer api support send CloudEvents in runtime
• support the implementation in connector-plugin for send CloudEvents to EventStore

Server side for subscribe

• support change the RocketMessage to CloudEvent in connector-plugin

• overwrite the AsyncMessageListener.consume() function, change the input parameter Message to CloudEvent

• update the MeshMQPushConsumer.updateOffset() implementation change the the input parameter Message to CloudEvent

• update DownStreamMsgContext , change the input parameter Message to CloudEvent, update the DownStreamMsgContext.ackMsg

For HTTP

SDK side for publish

• support LiteProducer.publish(cloudEvent)
• add the CloudEvents identifier in http request header

SDK side for subscribe

Server side for publish

• support build the HttpCommand.body by pluggable protocol plugins according the protocol type in HttpCommand header
• support publish the CloudEvent in message processors

Server side for subscribe

• update the EventMeshConsumer.subscribe()

• update HandleMsgContext , change the input parameter Message to CloudEvent

• update AsyncHttpPushRequest.tryHTTPRequest()

Appendix

References

• https://cloudevents.github.io/sdk-java/kafka