CQRS and Event Sourcing with Durable Execution

This repository demonstrates how to implement event-sourced applications in the context of durable execution using Restate and the Axon technology stack.

Installation of Restate and Axon Server

To install the required dependencies, follow the respective guides:

• Restate Quickstart

• Axon Server

  Note: After following the Axon Server installation instructions, in the axonserver.properties file add the following:

  axoniq.axonserver.devmode.enabled=true

Overview

The code samples include:

• Aggregates with Virtual Objects

  restate/src/ex1 illustrates how to implement an event-sourced aggregate, where its event stream (as well as its current state that is hydrated from said event stream) is stored as K/V state in a Restate Virtual Object. Commands and queries are sent to - and handled by - corresponding VO handlers.

• Utilizing an external event store and building Workflows

  restate/src/ex2 illustrates how to build a Restate Workflow (for renting a bike) that is triggered by - and interacts with - a standalone application implemented with Axon Framework, with events stored in Axon Server.

  The Axon application is found in the axon directory.

Restate

To enable a Restate code sample, uncomment the corresponding line in restate/src/app.ts.

Ensure that the Restate server is running before starting the Restate code samples.

To run a Restate code sample:

• Start it:

  npm run app-dev
  

• Register its Restate services.

  E.g. to register the Virtual Object in restate/src/ex1:

  restate dp add http://localhost:9080
  

• Deregister its Restate services.

  E.g. to deregister the Virtual Object in restate/src/ex1:

  restate dp remove [Virtual Object DEPLOYMENT_ID]
  

Axon

Build and run the Axon Framework application (in your IDE or with Maven).

Ensure that Axon Server is set up and running before starting the Axon Framework application.

Samples

Overview of the code samples.

The restate/src/ex1 and restate/src/ex2 samples demonstrate two approaches to implementing the event model depicted in em_bikerental.pdf.

Aggregates with Virtual Objects

A Restate Virtual Object encapsulates a domain model (command-side), read models, and orchestrates a business flow.

After starting the example application:

• Register the Restate services BikeObject and BikeService, running locally on ports 9080 and 9081 respectively.

• Open the Restate UI and in the playground execute the bike rental flow by invoking the following handlers:

  • registerBike

    Register a bike.

  • requestBike

    Request a bike.

    Pass along a JSON body of

    { "renter": "NameOfRenter" }.
    

  • returnBike

    Return a bike.

• Deregister the Restate services.

Utilizing an external event store and building Workflows

After starting both the Restate and Axon applications:

• Register the Restate services BikeWorkflow and BikeService, running locally on ports 9080 and 9081 respectively.

• Send the following HTTP requests to the Axon application (running locally on port 8888):

  • POST http://localhost:8888/setup?bikes=1

    Register a bike.

  • GET http://localhost:8888/bikes

    Get the bike identifier.

  • POST http://localhost:8888/requestBike?bikeId=<bikeId>&renter=<nameOfRenter>

    Request a bike with its identifier and name of renter.

  • POST http://localhost:8888/returnBike?bikeId=<bikeId>

    Return a bike with its identifier.

  To inspect the workflow, after requesting the bike open the Restate UI and navigate to Invocations; the bike rental workflow will be running and currently awaiting the bike's return.

• Deregister the Restate services.