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https://github.com/eventuate-tram/eventuate-tram-examples-customers-and-orders

An example of Choreography-based sagas in Spring Boot/JPA microservices
https://github.com/eventuate-tram/eventuate-tram-examples-customers-and-orders

eventual-consistency java microservice-architecture microservices sagas spring-boot

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An example of Choreography-based sagas in Spring Boot/JPA microservices

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README 

        
= An Eventuate project



image::https://eventuate.io/i/logo.gif[]



This project is part of http://eventuate.io[Eventuate], which is a microservices collaboration platform.



# Eventuate Tram Customers and Orders



This application demonstrates two key patterns:



* http://microservices.io/patterns/data/saga.html[Sagas] - implement transactions that span services

* http://microservices.io/patterns/data/cqrs.html[CQRS] - implement queries that retrieve data from multiple services.



The application consists of three services:



* `Order Service` - manages orders

* `Customer Service` - manages customers

* `Order History Service` - maintains the order history



All services are implemented using Spring Boot, JPA and the https://github.com/eventuate-tram/eventuate-tram-core[Eventuate Tram framework], which provides transactional publish/subscribe.



The `Order Service` uses a choreography-based saga to enforce the customer's credit limit when creating orders.



The `Order History Service` implements a CQRS view and subscribes to domain events published by the `Order Service` and `Customer Service`



Scroll down to get a tour of a code within a Github Codespace or Visual Studio Code.



== About Sagas



http://microservices.io/patterns/data/saga.html[Sagas] are a mechanism for maintaining data consistency in a http://microservices.io/patterns/microservices.html[microservice architecture].

A saga is a sequence of transactions, each of which is local to a service.



There are two main ways to coordinate sagas: orchestration and choreography.

This example uses choreography-based sagas, which use domain events for coordination.

Each step of a saga updates the local database and publishes a domain event.

The domain event is processed by an event handler, which performs the next local transaction.



To learn more about why you need sagas if you are using microservices:



* Look at the https://github.com/eventuate-tram/eventuate-tram-sagas-examples-customers-and-orders[Orchestration-based saga example]

* Read the http://microservices.io/patterns/data/saga.html[Saga pattern]

* Look at https://microservices.io/microservices/general/2019/04/28/asynchronous-microservices.html[MicroCPH 2019 presentation]

* Read about sagas in my https://microservices.io/book[Microservices patterns book]



=== The Create Order saga



The saga for creating an `Order` consists of the follow steps:



1. The Order Service creates an `Order` in a `PENDING` state and publishes an `OrderCreated` event

2. The `Customer Service` receives the event attempts to reserve credit for that `Order`. It publishes either a `Credit Reserved` event or a `CreditLimitExceeded` event.

3. The `Order Service` receives the event and changes the state of the order to either `APPROVED` or `REJECTED`.



== About Command Query Responsibility Segregation (CQRS)



The http://microservices.io/patterns/data/cqrs.html[CQRS pattern] implements queries that retrieves data from multiple services.

It maintains a queryable replica of the data by subscribing to domain events published by the services that own the data.



In this example, the `Order History Service`  maintains a CQRS view in MongoDB by subscribing to domain events published by the `Order Service` and `Customer Service`.

The CQRS view stores each customer as a MongoDB document that contains information the customer and their orders.



To learn more about why you need CQRS if you are using microservices:



* Read the http://microservices.io/patterns/data/cqrs.html[CQRS pattern]

* Look at https://microservices.io/microservices/general/2019/04/28/asynchronous-microservices.html[GOTO Chicago 2019 presentation]

* Read about CQRS in my https://microservices.io/book[Microservices patterns book]



== Transactional messaging with Eventuate Tram



The services uses the https://github.com/eventuate-tram/eventuate-tram-core[Eventuate Tram framework] to communicate asynchronously using events.

The flow for publishing a domain event using Eventuate Tram is as follows:



1. Eventuate Tram inserts events into the `MESSAGE` table as part of the ACID transaction that updates the JPA entity.

2. The Eventuate Tram CDC service tracks inserts into the `MESSAGE` table using the MySQL binlog (or Postgres WAL) and publishes messages to Apache Kafka.

3. A service subscribes to the events, updates its database, and possibly publishes more events.



== Architecture



The following diagram shows the architecture of the Customers and Orders application.



image::./images/Eventuate_Tram_Customer_and_Order_Architecture.png[]



The application consists of three services: `Customer Service`, `Order Service`, and `Order History Service`



=== Customer Service



The `Customer Service` implements a REST API for managing customers.

The service persists the `Customer` JPA entity in a MySQL/MsSQL/Postgres database.

Using `Eventuate Tram`, it publishes `Customer` domain events that are consumed by the `Order Service`.



For more information, see the link:./customer-service-canvas.adoc[microservice canvas for the `Customer Service`].



image::./customer-service-canvas.png[width=300]



=== Order Service



The `Order Service` implements REST API for managing orders.

The service persists the `Order` JPA entity in MySQL/MsSQL/Postgres database.

Using `Eventuate Tram`, it publishes `Order` domain events that are consumed by the `Customer Service`.



For more information, see the link:./order-service-canvas.adoc[microservice canvas for the `Order Service`].



image::./order-service-canvas.png[width=300]



=== Order History Service



The `Order History Service` implements REST API for querying a customer's order history

This service subscribes to events published by the `Order Service` and `Customer Service` and updates a MongoDB-based CQRS view.



For more information, see the link:./order-history-service-canvas.adoc[microservice canvas for the `Order History Service`].



image::./order-history-service-canvas.png[width=300]



== Building and running



Note: you do not need to install Gradle since it will be downloaded automatically.

You just need to have Java 8 installed.



First, build the application



```

./gradlew assemble

```



Next, launch the services using https://docs.docker.com/compose/[Docker Compose]:



```

./gradlew mysqlbinlogComposeBuild mysqlbinlogComposeUp

```



Note:



If the containers aren't accessible via `localhost` - e.g. you are using Docker Toolbox, you will have to use `${DOCKER_HOST_IP}` instead of localhost.

See this http://eventuate.io/docs/usingdocker.html[guide to setting `DOCKER_HOST_IP`] for more information.



You can also run the MsSQL version using `./gradlew mssqlpollingComposeUp` or Postgres version using `./gradlew postgreswalComposeUp`



== Using the application



Once the application has started, you can use the application via the Swagger UI:



* `Customer Service` - `http://localhost:8082/swagger-ui/index.html`

* `Order Service` - `http://localhost:8081/swagger-ui/index.html`

* `Order History Service` - `http://localhost:8083/swagger-ui/index.html`



You can also use `curl` to interact with the services.

First, let's create a customer:



```bash

$ curl -X POST --header "Content-Type: application/json" -d '{

  "creditLimit": {

    "amount": 5

  },

  "name": "Jane Doe"

}' http://localhost:8082/customers



HTTP/1.1 200

Content-Type: application/json;charset=UTF-8



{

  "customerId": 1

}

```



Next, create an order:



```bash

$ curl -X POST --header "Content-Type: application/json" -d '{

  "customerId": 1,

  "orderTotal": {

    "amount": 4

  }

}' http://localhost:8081/orders



HTTP/1.1 200

Content-Type: application/json;charset=UTF-8



{

  "orderId": 1

}



```



Next, check the status of the `Order` in the `Order Service`:



```bash

$ curl -X GET http://localhost:8081/orders/1



HTTP/1.1 200

Content-Type: application/json;charset=UTF-8



{

  "orderId": 1,

  "orderState": "APPROVED"

}

```



Finally, look at the customer's order history in the `Order History Service`:



```bash

$ curl -X GET --header "Accept: */*" "http://localhost:8083/customers/1"



HTTP/1.1 200

Content-Type: application/json;charset=UTF-8



{

  "id": 1,

  "orders": {

    "1": {

      "state": "APPROVED",

      "orderTotal": {

        "amount": 4

      }

    }

  },

  "name": "Chris",

  "creditLimit": {

    "amount": 100

  }

}

```



== Get a tour of the code



I've configured a https://marketplace.visualstudio.com/items?itemName=vsls-contrib.codetour[Code Tour] that will walk through the code in either Visual Studio Code or Github Codespaces.



=== In Visual Studio Code



1. If necessary, install the Code Tour extension from the Visual Studio Code Marketplace.

2. Use the `CodeTour: Start Tour` command from the command palette to start the tour.



=== In a Github Codespace



++++

    

      
  1. 

    Create a codespace.
    2. 

      
  2. If necessary, install the Code Tour extension from the Visual Studio Code Marketplace.
    3. 

      
  3. Use the CodeTour: Start Tour command from the command palette to start the tour.
    4. 



++++



== Got questions?



Don't hesitate to create an issue or see



* https://groups.google.com/d/forum/eventuate-users[Mailing list]

* https://join.slack.com/t/eventuate-users/shared_invite/enQtNTM4NjE0OTMzMDQ3LTc3ZjYzYjYxOGViNTdjMThkZmVmNWQzZWMwZmQyYzhjNjQ4OTE4YzJiYTE2NDdlOTljMDFlMDlkYTI2OWU1NTk[Slack Workspace]

* http://eventuate.io/contact.html[Contact us].