Circuit breaker account loan

Getting started

Many of us occasionally come across a loan possibility in our bank application, if we meet a special criteria. Let's imaging we have a loan microservice, which allow us to take a loan, but only when it's running.

Prerequisite

• Framework: Spring Boot 3.1.5 / Resilience4j Circuit Breaker
• Language: Java 17
• Build Tool: Maven

Spring Boot Backend

./mvnw clean install

Run docker containers via docker compose

docker-compose up -d

Testing

Step (1)

curl -X POST localhost:8081/loans/eligibility -d '{"balance": "20000"}' -H "Content-Type: application/json"
curl -X POST localhost:8080/accounts -d '{"firstname": "Tom", "surname": "Jenkins", "initialBalance": "2300"}' -H "Content-Type: application/json"
curl -X POST localhost:8080/accounts -d '{"firstname": "Andrew", "surname": "Hadley", "initialBalance": "20"}' -H "Content-Type: application/json"

Step (2) - Circuit Closed State

curl -X GET localhost:8080/accounts
curl -X GET localhost:8080/accounts/{id}
curl -X GET localhost:8080/actuator/health

At this point loan service is running, so we should see below in the response

"loanEligibility":{"maxAmount":4600.00,"maxMonthsTerm":60,"eligible":true}

Step (3) - Circuit Open State

After N tries circuit breaker changes the state to open

docker-compose stop loan
curl -X GET localhost:8080/accounts/{id}
curl -X GET localhost:8080/accounts/{id}
curl -X GET localhost:8080/accounts/{id}
curl -X GET localhost:8080/actuator/health

Loan service is not running, so we should see below in the response

"loanEligibility":{"maxAmount":0,"maxMonthsTerm":0,"eligible":false}

Step (4) - Circuit Half Open State

docker-compose up loan
curl -X GET localhost:8080/accounts/{id}
curl -X GET localhost:8080/accounts/{id}
curl -X GET localhost:8080/accounts/{id}
curl -X GET localhost:8080/actuator/health