DDD-lite Expense tracker application

Introduction

This application is made to showcase DDD-Lite within a modular monolith application. The motivation behind this is to show that a monolith can be implemented consistently and easily migrated to a microservice architecture ,if needed, some time in the future.

The application represents an expense tracker with a very limited set of features, but the intent is to demonstrate ,given a simplified business problem, how modules shall be implemented and put together.

Architecture

Features

The application exposes the following APIs, that cab be accessed through swagger at http://localhost:8080/swagger-ui.html#/

• Create user

• Add an expense

• Get expenses by user

• Get audit trail

Technical Environment

Expense tracker is a self contained application based on Spring Boot that runs an embedded servlet container running by default on port 8080 that expose a REST API.

The following list the main frameworks and libraries used to implement this application:

• spring boot: Simple and rapid framework to create simple and web based applications.
• lombok : Framework auto generating code for java (getter, setter, ...).
• vavr: Functional library for java.
• h2 : Lightweight in-memory relational database.
• swagger: Specification for machine-readable interface files for describing, producing, consuming, and visualizing RESTful web services
• spock: BDD-style testing and specification framework for Java and Groovy.

Requirements

• Java 11
• Groovy 2.5 or higher
• Maven 3.5 or higher
• Docker (optional)
• Kubernetes (optional)

Build

mvn clean package 

Run the application

IDE

Run the main class com.sy.expense.tracker.server.ExpenseTrackerApplication.

Maven

Open your terminal, navigate to the ExpenseTrackerApplication source directory then enter server directory. Run the following command:

mvn spring-boot:run

Java

Open your terminal, navigate to the ExpenseTrackerApplication source directory then enter server directory. Run the following command:

java -jar target/server-1.0-0-SNAPSHOT.jar

Docker

Open your terminal, navigate to the ExpenseTrackerApplication source directory then enter the server directory. Run the following command:

mvn compile jib:dockerBuild

The command above dockerize and install the application in your local docker daemon. You can issue the following command to view the docker image of the application

docker images

then issue the following the command to run the docker container:

docker run -p 8080:8080 sy/expense-tracker:1.0.0-SNAPSHOT

Kubernetes

Setup the docker registry

• If you run mini-kube make sure that Kubernetes is able to use your local docker daemon by issuing the following command:

eval $(minikube docker-env)

• If you use docker desktop everything should work out of the box.

Deploy the application

• Open your terminal, navigate to the server/kubernetes directory then issue the following commands:

kubectl apply -f server/kubernetes/expense-tracker-deployment.yaml
kubectl apply -f server/kubernetes/expense-tracker-service.yaml

You should have this when issuing the commands:

kubectl get pods

kubectl get services

• Open your terminal, run the following access so that the application can be accessible from your terminal or browser

kubectl port-forward svc/expense-tracker-service 8080:8080