Step 5: Try a Request-Reply Message Exchange Pattern

You've now completed Step 4: Try a Publish-Subscribe / Fan-Out Message Exchange Pattern.

In step 5, you'll expand your EDA by setting up a request-reply message exchange.

With request-reply messaging, applications achieve two-way communication using separate point-to-point channels: one for requests, and another for replies. In a request-reply pattern, the applications are both producers and consumers.

diagram illustrating the concepts described in the surrounding text

In the Solly's Coffee OMS we introduced in step 3, a Third-Party App sends a new order event as a request to the Order Management application whenever a user places an order. Upon receiving the request, the Order Management application replies with the order-id in the response. This interaction uses a request-reply message exchange, ensuring that the order confirmation is received synchronously.

Set Up a Request-Reply Message Exchange

In this exercise we'll set up two applications, Order Management and Third-Party App. After you complete these steps you'll have a message exchange pattern like the following animation:

Animation showing a request-reply message exchange

To set up a request-reply message exchange, perform these steps:

Open two command-line terminal windows, one for each application.
In terminal 1, set up the Order Management application with a subscription to the topic, coffeeshop/order/details/v1/*/ca/> that replies to requests with a payload containing a status and orderId. { status: 'Accepted', orderID: '12738' }. Enter the following command:

stm reply --topic "coffeeshop/order/new/v1/*/ca/>" --client-name "Order Management" --message "{status: 'Accepted', orderId: '12738'}"

You should see the following result:

ℹ  info      info: loading 'reply' command from configuration 'stm-cli-config.json'
…  waiting   connecting to broker [ws://localhost:8008, vpn: default, username: default, password: ******]
ℹ  info      info: client name: Order Management
✔  success   success: === Order Management successfully connected and ready to subscribe to request topic. ===
ℹ  info      info: subscribing to coffeeshop/order/new/v1/*/ca/>
ℹ  info      info: press Ctrl-C to exit
✔  success   success: successfully subscribed to request topic: coffeeshop/order/new/v1/*/ca/>
…  waiting   === ready to receive requests. ===

In terminal 2, set up the Third-Party App to send a request message with the topic, coffeeshop/order/new/v1/mobile/ca/437/4334. The application waits for a default time of 10 seconds to receive a reply before generating a time-out error.

stm request --topic "coffeeshop/order/new/v1/mobile/ca/437/4334" --client-name "Third Party App" --file order.json

You should see the following result:

ℹ  info      info: loading 'request' command from configuration 'stm-cli-config.json'
…  waiting   connecting to broker [ws://localhost:8008, vpn: default, username: default, password: ******]
ℹ  info      info: client name: Third Party App
✔  success   success: === Third Party App successfully connected and ready to send requests. ===
…  waiting   requesting...
✔  success   success: request sent on topic coffeeshop/order/new/v1/mobile/ca/437/4334
ℹ  info      info: Message Properties
Destination:                            [Topic coffeeshop/order/new/v1/mobile/ca/437/4334]
Class Of Service:                       COS1
DeliveryMode:                           DIRECT
ℹ  info      info: Message Payload (bytes): 659
✔  success   success: reply Received - [Topic coffeeshop/order/new/v1/mobile/ca/437/4334], type - TEXT
ℹ  info      info: Message Properties
Destination:                            [Topic #P2P/v:solbroker/mPuoLl8m/3rd Party App/_]
CorrelationId:                          #REQ1
Class Of Service:                       COS1
DeliveryMode:                           DIRECT
Reply Message
Binary Attachment:                      len=41
ℹ  info      info: Message Payload (bytes): 38
✔  success   success: disconnecting from Solace PubSub+ Event Broker...
✔  success   success: disconnected.
✔  success   success: exiting...

Third Party App sends a request message to Order Management with a new order. Order Management replies to the request with a message of { status: 'Accepted', orderID: '12738' }.

Press Control+C (on Windows and Linux) or Command+C (on Mac), to stop the applications.

Tutorial Steps

You've completed the fifth step in the tutorial. Click Next Steps for suggestions to continue your Solace journey.

Step	Description
	Set up Your First Event Broker - Complete
	Solace EDA Basics - Complete
	Set up the Solace Try-Me CLI Tool - Complete
	Try a Publish-Subscribe Message Exchange Pattern - Complete
	Try a Request-Reply Message Exchange Pattern - Complete
	Explore Consumer Scaling Patterns - Next Lesson
	Next Steps

You can return to the main Tutorial page at any time.

Provide feedback