liviu-florin-ilie / gaming-wallet

gaming-wallet

Getting Started

In order run the app you need to:
    1. start the Axon Server: 
         a.  docker run -d --name axonserver -p 8024:8024 -p 8124:8124 axoniq/axonserver
         or               
         b. download the jar from https://download.axoniq.io/axonserver/AxonServer.zip 
            and run it with  java -jar
    2. start the app with  mvn spring-boot:run from the root folder

Testing

• Swagger interface: http://localhost:8080/swagger-ui.html
• An additional create wallet action is implemented: http://localhost:8080/wallet .
• H2 Console: http://localhost:8080/h2-console/
• Axon server can also be checked: http://localhost:8024/

Frameworks

• Spring boot
• Axon Framework + Server
• H2
• Swagger

Choices

I chose CQRS + Event Sourcing approach. For that I used SpringBoot, Axon Framework and Axon Server.
CQRS + ES comes with some inherent advantages:

• extremely get accurate audit logging for free
• the ability to run temporal queries
• it extremely easy to reconstruct the historical state of the object
• we can clearly see the sequence of events occurring on the wallet account
• Axon is a lightweight framework that helps in building microservices

Command examples

• Create wallet command:

curl -X POST "http://localhost:8080/wallet" -H "accept: */*" -H "Content-Type: application/json" -d "{ \"initialBalance\": 100, \"username\": \"Player1\"}"
curl -X POST "http://localhost:8080/wallet" -H "accept: */*" -H "Content-Type: application/json" -d "{ \"initialBalance\": 100, \"username\": \"Player2\"}"

• Credit commands

curl -X PUT "http://localhost:8080/wallet/credit/yourWalletID" -H "accept: */*" -H "Content-Type: application/json" -d "{ \"amount\": 5, \"transactionId\": \"1\"}"
curl -X PUT "http://localhost:8080/wallet/debit/yourWalletID" -H "accept: */*" -H "Content-Type: application/json" -d "{ \"amount\": 5, \"transactionId\": \"2\"}"

• Query commands

curl -X GET "http://localhost:8080/wallet/yourWalletID" -H "accept: */*"
curl -X GET "http://localhost:8080/wallet/yourWalletID/events" -H "accept: */*"

What else needs to be done

• Pagination
• Logging
• Security
• Containerization
• Load testing
• The existing transaction check is a sensitive issue,as it will need another approach as the table grows. For example: implement a caching solution: https://hazelcast.com/use-cases/jcache-provider/ Also the unique transaction id would be ideally dealt with in the calling service.
• More detailed error handling
• Split the Query and Command into 2 different microservices that can be scaled separately.

Application flow

@RestController
    => @Service
            => @Aggregate
                => @CommandHandler
                        => @EventHandler
                                => operations on @Aggregate 
                                => *Projection classes => @Repository