How to Use Azure Service Bus Topic: Simple Guide

To use an Azure Service Bus Topic, create a topic in your Service Bus namespace, then send messages to it. Subscribers can receive messages from the topic using subscriptions, enabling multiple receivers to get copies of the messages.

Syntax

An Azure Service Bus Topic is a messaging entity that allows sending messages to multiple subscribers. The main parts are:

• Namespace: Your Service Bus container.
• Topic: The message channel where messages are sent.
• Subscription: Named receivers that get copies of messages from the topic.
• Sender: The client that sends messages to the topic.
• Receiver: The client that listens to a subscription to receive messages.

javascript

const { ServiceBusClient } = require("@azure/service-bus");

const connectionString = "<Your-Service-Bus-Connection-String>";
const topicName = "<Your-Topic-Name>";
const subscriptionName = "<Your-Subscription-Name>";

// Create a Service Bus client
const sbClient = new ServiceBusClient(connectionString);

// Sender to send messages to the topic
const sender = sbClient.createSender(topicName);

// Receiver to receive messages from a subscription
const receiver = sbClient.createReceiver(topicName, subscriptionName);

Example

This example shows how to send a message to a topic and receive it from a subscription using Node.js SDK.

javascript

const { ServiceBusClient } = require("@azure/service-bus");

async function main() {
  const connectionString = "<Your-Service-Bus-Connection-String>";
  const topicName = "mytopic";
  const subscriptionName = "mysubscription";

  const sbClient = new ServiceBusClient(connectionString);
  const sender = sbClient.createSender(topicName);
  const receiver = sbClient.createReceiver(topicName, subscriptionName);

  // Send a message
  await sender.sendMessages({ body: "Hello, Service Bus Topic!" });
  console.log("Message sent to topic.");

  // Receive messages
  const messages = await receiver.receiveMessages(1, { maxWaitTimeInMs: 5000 });
  for (const message of messages) {
    console.log(`Received message: ${message.body}`);
    await receiver.completeMessage(message);
  }

  await sender.close();
  await receiver.close();
  await sbClient.close();
}

main().catch((err) => {
  console.error("Error occurred: ", err);
});

Output

Message sent to topic.
Received message: Hello, Service Bus Topic!

Common Pitfalls

• Not creating subscriptions before receiving messages causes errors because subscriptions define the message receivers.
• Forgetting to complete messages after processing leads to message redelivery.
• Using the topic name instead of subscription name when receiving messages will fail.
• Not closing clients can cause resource leaks.

javascript

/* Wrong: Receiving from topic without subscription */
const receiver = sbClient.createReceiver(topicName); // Missing subscription name

/* Right: Specify subscription name */
const receiver = sbClient.createReceiver(topicName, subscriptionName);

Quick Reference

Remember these key points when using Service Bus Topics:

• Use createSender(topicName) to send messages.
• Use createReceiver(topicName, subscriptionName) to receive messages.
• Always complete messages after processing with completeMessage().
• Close senders, receivers, and clients to free resources.

Key Takeaways

Create subscriptions before receiving messages from a topic.

Send messages using a sender client targeting the topic.

Receive messages from subscriptions, not directly from the topic.

Complete messages after processing to avoid duplicates.

Always close clients to release resources.