Simple ordering system demonstrating Event Driven Architecture using NestJs for microservices and NATS as the message broker for intercommunication between microservices using subject based messaging, wildcard subscriptions, request-response and event-based message styles.
This repository utilizes NestJs monorepo workspaces to share re-usable code and modules across services, NATS module and NATS wildcard subscriptions.
NOTE: This personal project was rushed as a learning/upskilling exercise and is not production quality.
This system is using Subject-Based Messaging where the publisher sends a message to the NATS server. A subject is just a string of characters that form a name which the publisher and subscriber can use to find each other. The subscribing services use the direct string or wildcards to subscribe to the subjects it wants to listen for.
Services and their subjects:
- Intermediary service acts as a publisher, accepting RESTful HTTP requests and then emits/sends a message depending on the message style e.g. request-response or event-based (fire & forget).
- Messages to create (fire and forget) an order are emitted by making a POST request to the
/intermediary/orderendpoint. - Messages to retrieve (request-response) a list of inventory by making a GET request to the
/intermediary/inventoryendpoint.
- Messages to create (fire and forget) an order are emitted by making a POST request to the
- Order service subscribes to the subject
shop.order.placedand will perform the following:- Validates stock is available for the order by sending a message to the Inventory service using request-response pattern.
- Creates an order and stores it in the DB. Once the transaction is committed, it will emit a message to the Inventory service (fire and forget) to decrement the stock for those items.
- Inventory service subscribes to subjects using the direct string and
*,>wildcards.- Handler in the controller uses the catch all wildcard and inspects the context and handles the subject.
- Handler in the controlelr uses request-response pattern to list inventory to client.
- Docker
Use docker compose to setup the docker environment for the application and other services. The docker compose file contains all the configurations and commands required to build the services, database and seed the dataset into the db.
# Builds, (re)creates, starts, and attaches to containers for a service in detached mode. Ommit -d if you don't want to run in detached mode.
$ docker compose up -d
# If you want to rebuild
$ docker compose up -d --buildTo pre-populate the inventory table with data run the migrations after the services have started.
# Get the container id for inventory service
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
47a7811a7046 eda-nats-nestjs-order-service "docker-entrypoint.s…" 48 minutes ago Up 46 minutes order-service
413736db7d85 eda-nats-nestjs-inventory-service "docker-entrypoint.s…" 48 minutes ago Up 46 minutes inventory-service
bfba0a0e3152 eda-nats-nestjs-intermediary-service "docker-entrypoint.s…" 48 minutes ago Up 46 minutes 0.0.0.0:3000->3000/tcp intermediary-service
7a6051d761fd postgres:latest "docker-entrypoint.s…" 48 minutes ago Up 47 minutes 0.0.0.0:5432->5432/tcp shopdb
c863439ac926 nats:latest "/nats-server --conf…" 9 hours ago Exited (1) 26 minutes ago nats-server
# Open a terminal (e.g. a bash shell) to the container
$ docker exec -it <container_id_or_name> /bin/sh
# Run the migration script
$ npm run typeorm:run-migrationsAfter starting up the services via docker from the previous step, you can query the system with the following request.
# Placing an order on the frontend after selecting items to order from the displayed inventory.
curl -X POST http://localhost:3000/api/order \
-H "Content-Type: application/json" \
-d '{
"customer_name": "Adrian",
"customer_email": "test@test.com",
"order_items": [
{
"id": 1,
"product_name": "Laptop Stand",
"quantity": 3,
"price": 35
},
{
"id": 2,
"product_name": "Mouse Pad",
"quantity": 4,
"price": 25
}
]
}'Terminal logs for creating an order:
intermediary-service | [Nest] 523 - 09/05/2023, 3:42:27 AM LOG [IntermediaryService] Order successfully published.
logging-service | [Nest] 723 - 09/05/2023, 3:42:27 AM LOG [LoggingServiceController] handleLog(): shop.order.placed
logging-service | [Nest] 723 - 09/05/2023, 3:42:27 AM LOG [LoggingService] {"routing_key":"shop.order.placed","exchange":"shop.topic","payload":{"customer_name":"Adrian","customer_email":"test@test.com","order_items":[{"id":1,"product_name":"Laptop Stand","quantity":3,"price":35},{"id":2,"product_name":"Mouse Pad","quantity":4,"price":25}]},"status":"success","error_message":""}
logging-service | [Nest] 723 - 09/05/2023, 3:42:27 AM LOG [LoggingService] Log created with ID: 11
inventory-service | [Nest] 488 - 09/05/2023, 3:42:27 AM LOG [InventoryService] Stock is available for items: [{"id":1,"product_name":"Laptop Stand","quantity":3,"price":35},{"id":2,"product_name":"Mouse Pad","quantity":4,"price":25}]
order-service | [Nest] 210 - 09/05/2023, 3:42:27 AM LOG [OrderService] Stock available for all items in order: {"customer_name":"Adrian","customer_email":"test@test.com","order_items":[{"id":1,"product_name":"Laptop Stand","quantity":3,"price":35},{"id":2,"product_name":"Mouse Pad","quantity":4,"price":25}]}
order-service | [Nest] 210 - 09/05/2023, 3:42:27 AM LOG [OrderService] Saved order items: [{"product_name":"Laptop Stand","quantity":3,"price":35,"id":29},{"product_name":"Mouse Pad","quantity":4,"price":25,"id":30}]
order-service | [Nest] 210 - 09/05/2023, 3:42:27 AM LOG [OrderService] Order created: {"customer_name":"Adrian","customer_email":"test@test.com","total_items":7,"total_value":205,"order_items":[{"product_name":"Laptop Stand","quantity":3,"price":35,"id":29},{"product_name":"Mouse Pad","quantity":4,"price":25,"id":30}],"id":15,"created_at":"2023-09-05T03:42:27.687Z","updated_at":"2023-09-05T03:42:27.687Z"}.
logging-service | [Nest] 723 - 09/05/2023, 3:42:27 AM LOG [LoggingServiceController] handleLog(): shop.inventory.decrement.quantity
inventory-service | [Nest] 488 - 09/05/2023, 3:42:27 AM LOG [InventoryServiceController] handleInventory(): shop.inventory.decrement.quantity
logging-service | [Nest] 723 - 09/05/2023, 3:42:27 AM LOG [LoggingService] {"routing_key":"shop.inventory.decrement.quantity","exchange":"shop.topic","payload":[{"id":1,"product_name":"Laptop Stand","quantity":3,"price":35},{"id":2,"product_name":"Mouse Pad","quantity":4,"price":25}],"status":"success","error_message":""}
logging-service | [Nest] 723 - 09/05/2023, 3:42:27 AM LOG [LoggingService] Log created with ID: 12
inventory-service | [Nest] 488 - 09/05/2023, 3:42:27 AM LOG [InventoryService] Updated stock quantity for item: {"id":1,"product_name":"Laptop","quantity":129,"price":"1000","created_at":"2023-09-04T04:13:21.165Z","updated_at":"2023-09-05T03:42:27.802Z"}
inventory-service | [Nest] 488 - 09/05/2023, 3:42:27 AM LOG [InventoryService] Updated stock quantity for item: {"id":2,"product_name":"Phone","quantity":172,"price":"500","created_at":"2023-09-04T04:13:21.165Z","updated_at":"2023-09-05T03:42:27.802Z"}
# Retrieving all of the inventory items using request-response message style.
curl -X GET http://localhost:3000/api/inventory \
-H "Content-Type: application/json"Response
[
{
"id": 1,
"product_name": "Laptop",
"quantity": "47",
"price": "1000",
"created_at": "2023-09-07T07:17:09.336Z",
"updated_at": "2023-09-07T13:35:12.164Z"
},
{
"id": 2,
"product_name": "Phone",
"quantity": "196",
"price": "500",
"created_at": "2023-09-07T07:17:09.336Z",
"updated_at": "2023-09-07T13:35:12.164Z"
},
{
"id": 3,
"product_name": "Keyboard",
"quantity": "100",
"price": "50",
"created_at": "2023-09-07T07:17:09.336Z",
"updated_at": "2023-09-07T07:17:09.336Z"
},
{
"id": 4,
"product_name": "Mouse",
"quantity": "100",
"price": "45",
"created_at": "2023-09-07T07:17:09.336Z",
"updated_at": "2023-09-07T07:17:09.336Z"
},
{
"id": 5,
"product_name": "Laptop Stand",
"quantity": "150",
"price": "35",
"created_at": "2023-09-07T07:17:09.336Z",
"updated_at": "2023-09-07T07:17:09.336Z"
},
{
"id": 6,
"product_name": "Mouse Pad",
"quantity": "200",
"price": "25",
"created_at": "2023-09-07T07:17:09.336Z",
"updated_at": "2023-09-07T07:17:09.336Z"
},
{
"id": 7,
"product_name": "Phone Case",
"quantity": "175",
"price": "30",
"created_at": "2023-09-07T07:17:09.336Z",
"updated_at": "2023-09-07T07:17:09.336Z"
},
{
"id": 8,
"product_name": "KVM Switch",
"quantity": "100",
"price": "175",
"created_at": "2023-09-07T07:17:09.336Z",
"updated_at": "2023-09-07T07:17:09.336Z"
}
]