Saga Orchestration Pattern: Use Case Implementation

Transactional Outbox + Change Data Capture with Debezium

Tech Stack: Java 21, Spring-Boot and Apache Kafka

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This use case demonstrates how to implement the SAGA Pattern to achieve distributed transactions across multiple microservices, assuming the implementation utilizes a Database per Service approach. The solution employs the Transactional Outbox Pattern in conjunction with Change Data Capture (CDC) and Debezium on top of Kafka Connect, and, Apache Kafka serves as the messaging backbone for the overall architecture.

Context:

Use case: As a guest, I want to make a hotel reservation

There are 3 microservices involved:

• Reservation Service - initiator and orchestrator of the Saga
• Hotel Service - ensure the hotel's room requested is available and book it or rejects it if unavailable
• Payment Service - executes the payment associated to an incoming reservation

And we have the following service configuration:

Task:

Use the SAGA Orchestration Pattern to ensure data consistency between services.

Implementation

The reservation process is as follows:

The SAGA framework state machine happy path:

A detailed component workflow:

A happy path for making a reservation is illustrated in the following sequence diagram:

An unhappy path of making a reservation, when the payment is rejected, and the compensation step is involved you can see in the following sequence diagram:

Running the Use Case

Start the docker compose (docker-compose.yaml)

% docker-compose up --build

During the build process there is a kafka-setup service which submit the debezium connectors

Make a reservation

% http POST http://localhost:8080/api/v1/reservations < e2e/room-reservation-placement.json

HTTP/1.1 202
Location: http://localhost:8080/api/v1/reservations/9a40b57d-36a1-4991-9b72-afdd41c154c0
Retry-After: 0.5

Examine the emitted event for room-booking.inbox.events in Apache Kafka:

% docker run --tty --rm \
    --network saga-orchestration-network \
    quay.io/debezium/tooling:1.2 \
    kafkacat -b kafka:9092 -C -o beginning -q \
    -f "{\"key\":%k, \"headers\":\"%h\"}\n%s\n" \
    -t room-booking.inbox.events 
    
{"key":8877b9f1-28a0-42ef-9868-0288966f8a4c, "headers":"id=775f814a-4923-4f10-9b56-a4307a1ac800,eventType=REQUEST"}
{"type":"REQUEST","roomId":1,"endDate":"2023-12-17","guestId":10000001,"hotelId":1,"startDate":"2023-12-16","paymentDue":1702632793441,"creditCardNo":"************7999","reservationId":"9a40b57d-36a1-4991-9b72-afdd41c154c0"}

and, the emitted event for payment.inbox.events in Apache Kafka:

% docker run --tty --rm \
    --network saga-orchestration-network \
    quay.io/debezium/tooling:1.2 \
    kafkacat -b kafka:9092 -C -o beginning -q \
    -f "{\"key\":%k, \"headers\":\"%h\"}\n%s\n" \
    -t payment.inbox.events 
    
{"key":8877b9f1-28a0-42ef-9868-0288966f8a4c, "headers":"id=1fb5030c-629a-4ec3-8b9b-57cdbb423309,eventType=REQUEST"}
{"type":"REQUEST","roomId":1,"endDate":"2023-12-17","guestId":10000001,"hotelId":1,"startDate":"2023-12-16","paymentDue":1702632793441,"creditCardNo":"************7999","reservationId":"9a40b57d-36a1-4991-9b72-afdd41c154c0"}

Query the saga state in the reservation service's database:

% docker run --tty --rm -i \
        --network saga-orchestration-network \
        quay.io/debezium/tooling:1.2 \
        bash -c 'pgcli postgresql://reservationuser:secret@reservation-db:5432/reservationdb'

SELECT * FROM public.sagastate;

+--------------------------------------+-----------+------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+-------------------------------------------------------+---------------+
| id                                   | version   | type             | payload                                                                                                                                                                                                                                           | current_step   | step_status                                           | saga_status   |
|--------------------------------------+-----------+------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+-------------------------------------------------------+---------------|
| 8877b9f1-28a0-42ef-9868-0288966f8a4c | 3         | room-reservation | {"type": "REQUEST", "roomId": 1, "endDate": "2023-12-17", "guestId": 10000001, "hotelId": 1, "startDate": "2023-12-16", "paymentDue": 1702632793441, "creditCardNo": "************7999", "reservationId": "9a40b57d-36a1-4991-9b72-afdd41c154c0"} | <null>         | {"payment": "SUCCEEDED", "room-booking": "SUCCEEDED"} | COMPLETED     |
+--------------------------------------+-----------+------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+-------------------------------------------------------+---------------+

And, also, query the location URL:

% http GET http://localhost:8080/api/v1/reservations/9a40b57d-36a1-4991-9b72-afdd41c154c0 
HTTP/1.1 200 
Content-Type: application/json

{
    "guestId": 10000001,
    "hotelId": 1,
    "reservationId": "9a40b57d-36a1-4991-9b72-afdd41c154c0",
    "roomId": 1,
    "status": "SUCCEED"
}

Checkout e2e folder with some unhappy scenarios

Run local using spring-boot:run

% docker-compose up --build --scale reservation-service=0 --scale payment-service=0 --scale hotel-service=0

% ./mvnw install

% ./mvnw  spring-boot:run -f hotel-service/pom.xml  -Dspring-boot.run.arguments="--POSTGRES_PORT=5433 --server.port=8081"

% ./mvnw  spring-boot:run -f payment-service/pom.xml  -Dspring-boot.run.arguments="--POSTGRES_PORT=5434 --server.port=8082"

% ./mvnw  spring-boot:run -f reservation-service/pom.xml  -Dspring-boot.run.arguments="--POSTGRES_PORT=5432 --server.port=8080"