Event Stream Application Workbench
Overview
ESAW helps you design applications built around Event Streams like you find in Apache Kafka. Traditional applications are typically modeled around domain objects and actions on those obects. An alternative way to look at applications is as an ongoing stream of events. For example, a user creates an account, the account is verified, and the user then makes a purchase.
| Action | Legacy Application | Event Stream Application |
|---|---|---|
| User creates an account | User Object created and persisted | USER.created Event |
| User's account is verified | User Object is updated as 'verified' | USER.verified Event |
| User makes a purchase | Purchase object is created and persisted | ORDER.created Event |
A key concept in Event Stream application is "the log is truth."
ESAW Concepts
Application
At the highest level of abstraction, you are creating what we call an application. Usually what we consider an application is the output of a single team of developers.
Applications are a collection of Processors which consume inputs and create outputs.
An application has the following properties...
| Name | Purpose |
|---|---|
| Name | The application name |
| Processor Repositories | List of repositories that define processors used by this application. |
| Event Definition Repositories | List of repositories that hold event definitions used by the processors in the application. |
| Payload Definition Repositories | List of repositories that hold payload definitions used by processors and event definitions. |
An application may have local processors, event definitions and payload definitions or it may share those entities from other applications.
Processors
Processors are the code that do things. You can think of these as microservices. A processor will have an input and an output. Input may be either a REST actions like POST, PUT, or DELETE, or it may be an Event Topic subscription. Output may be either a REST GET or an Event Topic production. The Processor code processes input and produces output.
Event Definitions
Events are the entities that are put on the Event Stream. They have a type, name and payload.
Payload Definitions
Payloads are the actual data entities carried by Events and worked on by Processors. These are generally JSON objects but need not be.
Development
Installing
$ npm installRunning The App
Dev on port 3000.
$ npm run devProduction on port 3001.
$ npm run build
$ node server/server.js