Java 21, Spring Cloud based microservices application for renting cars. POC of the Spring Cloud microservices architecture written in DDD and hexagonal architecture.
https://github.com/maciejgz/rac
- Language - Java 21
- Frameworks - Spring Boot, Spring Cloud
- Database - MongoDB
- Message broker - Kafka
- Search - Elasticsearch
- Monitoring - Micrometer, Prometheus, Grafana
- Tracing - Zipkin
- Code analysis - Sonar
- Build tool - Gradle
- Containerization - Docker, Docker Compose
- User can search for a car to rent by his coordinates
- User can rent an available car
- Position of the car is constantly updated and available for the administrator
- User can return a car
- User can see a history of his rents
- Administrator can add or remove a car from the pool of the available cars
- User is charged for:
- distance traveled (to simplify - the distance is calculated as a difference between the current and the previous carLocation of the car) - 1$ per km
- time of the rent - 0.2$ per minute
- Gradle as a build tool
- DDD and hexagonal architecture - keep application and domain logic independent of the framework. All beans shall be created in the infrastructure layer config classes. The only exception are the transactional annotations in the application service layer.
- Domain events should be different from the events sent to the message broker. Domain events are used for internal communication between services. For the simplicity, we will use the same events for both internal and external communication.
- Domain services should operate on pure data without commands. Commands reach the application service layer and from there we pass on pure data or domain DTOs.
- Kafka as a message broker
- Internal communication between services by events with sagas
- Requests to the services through the API Gateway
- API Gateway receives a success message right after submission of rent request - then asynchronous commit is sent after successful saga execution
- In the final version use time series Cassandra column database for storing the car carLocation updates. At first - MongoDB shall be used.
- rac-api-gateway - 8080 - API gateway
- rac-user-service - 8081 - User management service
- rac-rent-service - 8082 - Renting service
- rac-search-service - 8083 - search functionality
- rac-car-service - 8084 - car fleet management
- rac-location-service - 8085 - gathering carLocation data of the cars and users. All the agents are sending the data to this service. Should use Cassandra column database for storing the carLocation data.
- rac-simulation-service - 8086 - simulates the data of the cars and users
- rac-discovery-service - http://localhost:8761/ - Spring Eureka server
- rac-configuration-service - 8888 - Spring Cloud Config
- MongoDB - 27017 - centralized database - each microservice will have a different schema
- Cassandra - 9042 - time series database for storing the car and user carLocation updates
- Message broker
- Kafka - 9092 - message broker
- Zookeeper
- Search
- Elasticsearch
- Kibana
- Zipkin - http://localhost:9411/ - distributed tracing service
- Monitoring
- Micrometer - observability facade
- Prometheus - time series database
- Grafana - http://localhost:9091/ - monitoring admin/admin
- Sonar - http://localhost:9000/ - code analysis
| component | port | comment | group |
|---|---|---|---|
| rac-api-gateway | 8080 | HTTP API Gateway | APP |
| rac-user-service | 8081 | user management service | APP |
| rac-rent-service | 8082 | renting service | APP |
| rac-search-service | 8083 | search service | APP |
| rac-car-service | 8084 | car fleet management | APP |
| rac-location-service | 8085 | Cars and users location service | APP |
| rac-simulation-service | 8086 | Simulation service | APP |
| rac-discovery-service | 8761 | Spring Cloud Eureka - discovery service | APP |
| rac-configuration-service | 8888 | Spring Cloud Config - centralized config service | APP |
| rac-mongodb | 27017 | MongoDB - database | DB |
| rac-cassandra | 9042 | Cassandra - database | DB |
| rac-kafka | 9092 | Kafka - Message broker | MESSAGE BROKER |
| rac-zookeeper | 2181 | Zookeeper - Kafka nodes synchronization service | MESSAGE BROKER |
| rac-elasticsearch | 9200 | Elasticsearch - for search... | SEARCH |
| rac-kibana | 5601 | Kibana - Web UI for Elasticsearch | SEARCH |
| rac-zipkin | 9411 | Zipkin - distributed tracing collector | DISTRIBUTED TRACING |
| rac-prometheus | 9090 | Prometheus - time series database receives data from Micrometer agents | MONITORING |
| rac-grafana | 9091 | Grafana - Web UI for the containers monitoring data stored in Prometheus | MONITORING |
| rac-sonar | 9000 | Sonar - code analysis | CODE ANALYSIS |
| event ID | topic | comment |
|---|---|---|
| RAC_USER_CREATED | RAC_USER | Sent when user is created |
| RAC_USER_DELETED | RAC_USER | Sent when user is deleted |
| RAC_USER_CHARGED | RAC_USER | Sent when user is charged for rent or due to some other reason |
| event ID | topic | comment |
|---|---|---|
| RAC_CAR_CREATED | RAC_CAR | Sent when car is added to the fleet |
| RAC_CAR_DELETED | RAC_CAR | Sent when user is deleted |
| RAC_CAR_RENT_SUCCESS | RAC_CAR | Sent when car is rented |
| RAC_CAR_RENT_FAILED_ALREADY_RENTED | RAC_CAR | Sent when car cannot be rented - already rented by other user |
| RAC_CAR_RENT_FAILED_NOT_EXIST | RAC_CAR | Sent when car cannot be rented - car already not exist in the pool |
| RAC_CAR_RETURN_SUCCESS | RAC_CAR | Sent when car is successfully returned from rental |
| RAC_CAR_RETURN_FAILED_ALREADY_RETURNED | RAC_CAR | Sent when car cannot be returned - already returned |
| RAC_CAR_RETURN_FAILED_NOT_EXIST | RAC_CAR | Sent when car cannot be returned - already returned |
| event ID | topic | comment |
|---|---|---|
| RAC_RENT_REQUEST_USER | RAC_RENT | Sent when rent is requested to validate request in the user service |
| RAC_RENT_REQUEST_CAR | RAC_RENT | Sent when rent is requested and confirmed in user service. Car service should validate the request |
| RAC_RENT_CONFIRMATION | RAC_RENT | Sent when rent is confirmed in car service and should be confirmed in rent service |
| RAC_RENT_FAILED_USER | RAC_RENT | Issue in rent validation in user service. Consumed by |
| RAC_RENT_FAILED_CAR | RAC_RENT | Issue in rent validation in car service |
| RAC_RENT_SUCCESS | RAC_RENT | Sent when rent is successfully created and accepted |
| event ID | topic | comment |
|---|---|---|
| RAC_RETURN_REQUEST_LOCATION | RAC_RETURN | Sent when return is requested to validate request and calculate distance traveled |
| RAC_RETURN_REQUEST_USER | RAC_RETURN | Sent when return is requested and confirmed in carLocation service to validate request in the user service |
| RAC_RETURN_REQUEST_CAR | RAC_RETURN | Sent when return is requested and confirmed in user service. Car service should validate the request |
| RAC_RETURN_CONFIRMATION | RAC_RETURN | Sent when return is confirmed in car service and should be confirmed in rent service |
| RAC_RETURN_FAILED_LOCATION | RAC_RETURN | Issue in return validation in carLocation service |
| RAC_RETURN_FAILED_USER | RAC_RETURN | Issue in return validation in user service |
| RAC_RETURN_FAILED_CAR | RAC_RETURN | Issue in return validation in car service |
| RAC_RETURN_SUCCESS | RAC_RETURN | Sent when return is confirmed and accepted |
| event ID | topic | comment |
|---|---|---|
| RAC_LOCATION_USER_CHANGED | RAC_LOCATION_USER | Sent when user has changed his carLocation |
| RAC_LOCATION_CAR_CHANGED | RAC_LOCATION_CAR | Sent when car has changed his carLocation |
- User sends a rent HTTP request to the API Gateway
- API Gateway sends a rent request to the rac-rent-service (HTTP)
- Rent service validates the request (final validation will be done in the last event) and checks if there is no active
or requested rent for the user and car.
- in case of success: creates a rent with status RENT_REQUESTED, starts a saga and sends a rent request to the rac-user-service (Kafka) - RAC_RENT_REQUEST_USER
- in case of failure: sends a rent failure to the api gateway (HTTP)
- User service validates the rent request. What should be validated: user exists, user is not blocked.
- in case of success - sends a rent request to the rac-car-service (Kafka) - RAC_RENT_REQUEST_CAR
- in case of failure - sends a rent failure to the rac-rent-service (Kafka) - RAC_RENT_FAILED_USER, then the saga is compensated in the rac-rent-service
- Car service validates the request. What should be validated: car exists, car is available, car is healthy.
- in case of success - sends a rent confirmation to the rac-rent-service (Kafka) - RAC_RENT_CONFIRMATION
- in case of failure - sends a rent failure to the rac-rent-service and rac-user-service (Kafka) - * RAC_RENT_FAILED_CAR*. Then the saga is compensated in the rac-rent-service
- Rent service receives RAC_RENT_CONFIRMATION message and validates if there is no active or requested rent for the user and car. If not, rent status is changed to RENT_CONFIRMED. Rent service sends an event: RAC_RENT_SUCCESS which is consumed by the car service and user service to fill in rentalId as a readonly cache used for search.
When a rental is initiated, customer and car GPS agents should increase the frequency of data sending to the carLocation service - once per 5s. Location service should update the car and user carLocation in the database and push notifications (RAC_LOCATION_USER_CHANGED, RAC_LOCATION_CAR_CHANGED) to Kafka (events consumed by the search, car, user and rent service). User is notified about the successful rent by the Websocket connection. In case of car failure, car healthcheck system sends contacts with car-service REST API to inform about failure. It should block user from returning the car and request contact the support.
- User sends a return HTTP request to the API Gateway
- API Gateway sends a return request to the rac-rent-service (HTTP)
- rac-rent-service validates the request: if there is an active rent for the user and car.
- in case of success - calculate distance traveled querying rac-carLocation-service by event (Kafka) - * RAC_RETURN_REQUEST_LOCATION*
- in case of failure - sends a return failure api gateway (HTTP)
- rac-location-service validates RAC_RETURN_REQUEST_LOCATION. In case of success:
- calculates the distance traveled and sends a return request to the rac-user-service (Kafka) - * RAC_RETURN_REQUEST_USER*
- in case of failure - sends a return failure to the rac-rent-service (Kafka) - RAC_RETURN_FAILED_LOCATION, then saga is compensated in the rac-rent-service
- rac-user-service receives the request and tries to charge the user:
- in case of success - charges user for the distance traveled (with proper policy), sends an event to the rac-car-service (Kafka) - RAC_RETURN_REQUEST_CAR
- in case of failure - sends a return failure to the rac-rent-service (Kafka) - RAC_RETURN_FAILED_USER, then the saga is compensated in the rac-rent-service
- rac-car-service validates the request (car health status, car exists) and:
- in case of validation success - sets the car as available and sends a return confirmation to the rac-rent-service (Kafka) - RAC_RETURN_CONFIRMATION.
- in case of validation failure - sends a return failure event to the rac-rent-service and rac-user-service ( Kafka) - RAC_RETURN_FAILED_CAR. Then the saga is compensated in the rac-rent-service (contact with support request) and rac-user-service (charged money is returned to the user).
- rac-rent-service receives RAC_RETURN_CONFIRMATION message and validates if there is an active rent for the user and car. If yes, rent status is changed to RENT_RETURNED. Rent service sends an event: RAC_RETURN_SUCCESS which is consumed by the car service and user service to clear rentalId as a readonly cache used for search.
When a rental is finished, customer and car GPS agents should decrease the frequency of data sending to the carLocation service - once per 30s. Location service should update the car and user carLocation in the database and push notifications ( RAC_LOCATION_USER_CHANGED, RAC_LOCATION_CAR_CHANGED) to Kafka (events consumed by the search, car, user and rent service). User is notified about the successful return by the Websocket connection.
Simulation service let to simulate the data of the cars and users. It is used for testing purposes. Simulation is configured through the config service. It is possible to configure the number of concurrent threads simulating active sessions of users and administrators adding or removing cars from the pool of available cars. Scenarios have a probability to be executed. It is possible to configure the probability of each scenario.
Possible simulation scenarios:
- User registers
- User unregisters
- Administrator adds a car
- Administrator removes a car from the pool of available cars
- User is locked by administrator - TODO
- User is unlocked by administrator - TODO
- Car is broken - TODO
- Car is fixed - TODO
- User rents a car - then localizations of the user and the car are updated and then user returns the car - success story
- User tries to rent already rented car
- Car's healthcheck system sends a message about car failure
Monitoring is based on Micrometer, Prometheus and Grafana. Each service has a Micrometer agent that sends metrics to the Prometheus. Prometheus is a time series database that stores metrics. Grafana is a Web UI for Prometheus. It is possible to create dashboards in Grafana. All the required components are deployed in the docker containers. Grafana is available in the browser under http://localhost:9091/ with admin/admin credentials. Prometheus is available in the browser under http://localhost:9090/ without any credentials.
Tracing is based on Zipkin. Each service has a Zipkin agent that sends traces to the Zipkin server. The same trace ID is
used for all the Kafka events and HTTP requests related to the same user request.
Kafka events contains header traceparent with the trace ID formatted as 00-<trace-id>-<span-id>-<trace-flags> (
like 00-fe6938c57a2d70d8f85f1373c26c39b0-638a54064ebea9f0-01)
Build with Gradle wrapper from the root repository directory:
.\gradlew.bat buildTo run Sonar code analysis, run the following command in the root repository directory with sonar container running locally. Then login with admin/admin credentials, change the password to admin1 and run the analysis with the following command:
.\gradlew.bat clean compileJava sonarTo run a project, at first, 3rd party services shall be started. To do so, run the following command in the docker directory:
.\start_3rd_party_components.bat Then run all the Spring Boot services with the following command in the root repository directory.
Test were written for the first 3 levels of the tests pyramid partially and only for the rac-user-service - as a POC.
- Unit tests are written with JUnit 5 and Mockito - https://junit.org/junit5/, https://site.mockito.org/
- Integration tests are written with Spring Boot Test and Testcontainers (Kafka, MongoDB) - https://www.testcontainers.org/
- Contract tests are written with Spring Cloud Contract - https://spring.io/projects/spring-cloud-contract/
- Resources:
Run unit tests with the following command in the root repository directory:
.\gradle.bat testRun integration tests with Docker running and Testcontainers and the following command in the root repository directory:
.\gradle.bat integrationTestTo be done. Run contract tests with the following command in the root repository directory:
.\gradle.bat contractTest