Service Bus topics and subscriptions in Azure - Commands & Configuration

Introduction

Sometimes, many parts of an app need to get messages separately. Service Bus topics and subscriptions let you send one message and have many parts receive it independently. This helps keep messages organized and shared safely.

When you want to send one message to many different parts of your app without mixing them up.

When different teams or services need to get only certain messages from a shared source.

When you want to keep messages safe and make sure no one misses important info.

When you want to separate message handling by topics so each subscriber gets only what they want.

When you want to scale message processing by adding more subscribers without changing the sender.

Config File - topic-subscription.json

topic-subscription.json

{
  "type": "Microsoft.ServiceBus/namespaces/topics",
  "apiVersion": "2021-06-01-preview",
  "name": "example-namespace/example-topic",
  "location": "eastus",
  "properties": {
    "defaultMessageTimeToLive": "P14D",
    "maxSizeInMegabytes": 1024
  }
}

{
  "type": "Microsoft.ServiceBus/namespaces/topics/subscriptions",
  "apiVersion": "2021-06-01-preview",
  "name": "example-namespace/example-topic/example-subscription",
  "properties": {
    "lockDuration": "PT1M",
    "maxDeliveryCount": 10,
    "defaultMessageTimeToLive": "P7D"
  }
}

The first JSON block creates a Service Bus topic named example-topic inside the namespace example-namespace. It sets the message time to live to 14 days and max size to 1 GB.

The second JSON block creates a subscription named example-subscription under the topic. It sets how long a message is locked during processing (1 minute), max delivery attempts (10), and message time to live (7 days).

Commands

Create a Service Bus namespace where topics and subscriptions will live. The Standard SKU supports topics and subscriptions.

Terminal

az servicebus namespace create --resource-group example-rg --name example-namespace --location eastus --sku Standard

Expected Output

{

  "createdAt": "2024-06-01T12:00:00Z",

  "location": "eastus",

  "name": "example-namespace",

  "provisioningState": "Succeeded",

  "resourceGroup": "example-rg",

  "sku": {

    "name": "Standard"

  },

  "type": "Microsoft.ServiceBus/namespaces"

}

→

--sku - Sets the pricing tier; Standard is needed for topics and subscriptions

Create a topic named example-topic in the namespace. This topic will hold messages for subscribers.

Terminal

az servicebus topic create --resource-group example-rg --namespace-name example-namespace --name example-topic --max-size 1024 --default-message-time-to-live 14

Expected Output

{

  "name": "example-topic",

  "maxSizeInMegabytes": 1024,

  "defaultMessageTimeToLive": "P14D",

  "status": "Active"

}

→

--max-size - Sets max size of the topic storage in MB

→

--default-message-time-to-live - Sets how long messages live before expiring

Create a subscription named example-subscription under the topic. This subscription will receive messages sent to the topic.

Terminal

az servicebus topic subscription create --resource-group example-rg --namespace-name example-namespace --topic-name example-topic --name example-subscription --lock-duration PT1M --max-delivery-count 10 --default-message-time-to-live 7

Expected Output

{

  "name": "example-subscription",

  "lockDuration": "PT1M",

  "maxDeliveryCount": 10,

  "defaultMessageTimeToLive": "P7D",

  "status": "Active"

}

→

--lock-duration - Sets how long a message is locked during processing

→

--max-delivery-count - Sets how many times a message can be delivered before dead-lettering

Check the details of the subscription to confirm it was created correctly.

Terminal

az servicebus topic subscription show --resource-group example-rg --namespace-name example-namespace --topic-name example-topic --name example-subscription

Expected Output

{

  "name": "example-subscription",

  "lockDuration": "PT1M",

  "maxDeliveryCount": 10,

  "defaultMessageTimeToLive": "P7D",

  "status": "Active"

}

Key Concept

If you remember nothing else from this pattern, remember: topics let you send one message to many independent subscribers who each get their own copy.

Common Mistakes

Trying to create a subscription before the topic exists

Subscriptions must belong to an existing topic, so creation fails if the topic is missing

Always create the topic first, then create subscriptions under it

Using Basic SKU namespace which does not support topics and subscriptions

Basic SKU only supports queues, so topic commands will fail

Use Standard or Premium SKU for namespaces that need topics and subscriptions

Setting lock duration too short causing message processing to fail

If lock duration is too short, messages may be delivered multiple times before processing finishes

Set lock duration long enough for your processing to complete, like 1 minute or more

Summary

Create a Service Bus namespace with Standard SKU to support topics and subscriptions.

Create a topic to hold messages that multiple subscribers can receive.

Create subscriptions under the topic to receive copies of messages independently.

Use commands to verify the topic and subscription are active and configured correctly.

Practice

1. What is the main purpose of an Azure Service Bus topic?

easy

A. To send messages to multiple receivers using subscriptions

B. To store data permanently like a database

C. To host web applications

D. To manage virtual machines

Solution

1. Step 1: Understand the role of a Service Bus topic

   A Service Bus topic acts as a message distributor that sends messages to multiple receivers.

2. Step 2: Compare other options

   Options B, C, and D describe unrelated Azure services or functions.

3. Final Answer:

   To send messages to multiple receivers using subscriptions -> Option A

4. Quick Check:

   Service Bus topic = message distribution [OK]

Hint: Topics distribute messages to many receivers via subscriptions [OK]

Common Mistakes:

• Confusing topics with queues
• Thinking topics store data permanently
• Mixing topics with compute services

2. Which of the following is the correct way to create a subscription under a topic using Azure CLI?

easy

A. az servicebus topic create --resource-group MyGroup --namespace-name MyNamespace --subscription-name MySubscription --name MyTopic

B. az servicebus subscription create --resource-group MyGroup --namespace-name MyNamespace --topic-name MyTopic --name MySubscription

C. az servicebus topic subscription create --resource-group MyGroup --namespace-name MyNamespace --topic-name MyTopic --name MySubscription

D. az servicebus create subscription --resource-group MyGroup --namespace-name MyNamespace --topic MyTopic --subscription MySubscription

Solution

1. Step 1: Identify the correct Azure CLI command structure

   The correct command to create a subscription under a topic is 'az servicebus subscription create' with required parameters.

2. Step 2: Check parameters and order

   az servicebus subscription create --resource-group MyGroup --namespace-name MyNamespace --topic-name MyTopic --name MySubscription uses the correct command and parameters: resource group, namespace, topic name, and subscription name.

3. Final Answer:

   az servicebus subscription create --resource-group MyGroup --namespace-name MyNamespace --topic-name MyTopic --name MySubscription -> Option B

4. Quick Check:

   Correct CLI syntax = az servicebus subscription create --resource-group MyGroup --namespace-name MyNamespace --topic-name MyTopic --name MySubscription [OK]

Hint: Use 'az servicebus subscription create' to add subscriptions [OK]

Common Mistakes:

• Using 'az servicebus topic create' for subscriptions
• Using invalid 'az servicebus topic subscription create'
• Incorrect command verbs or missing flags

3. Given the following code snippet, what will be the output?

from azure.servicebus import ServiceBusClient
connection_str = "Endpoint=sb://example.servicebus.windows.net/;SharedAccessKeyName=RootManageSharedAccessKey;SharedAccessKey=key"
topic_name = "mytopic"
subscription_name = "mysubscription"

with ServiceBusClient.from_connection_string(connection_str) as client:
    receiver = client.get_subscription_receiver(topic_name, subscription_name)
    with receiver:
        messages = receiver.receive_messages(max_message_count=2, max_wait_time=5)
        print(len(list(messages)))

medium

A. 2

B. The code will not compile

C. An exception is raised due to missing message processing

D. 0

Solution

1. Step 1: Understand message receiving behavior

   The code tries to receive up to 2 messages with a 5-second wait. If no messages are available, it returns an empty list.

2. Step 2: Analyze message processing

   Since no messages are explicitly sent before receiving, the list will be empty, so len(messages) is 0.

3. Final Answer:

   0 -> Option D

4. Quick Check:

   Receive without sent messages = 0 [OK]

Hint: Receiving messages without sending returns empty list [OK]

Common Mistakes:

• Assuming messages exist without sending
• Expecting exceptions for no messages
• Confusing receive_messages with peek_messages

4. You have created a subscription but messages are not being received. Which of the following is the most likely cause?

medium

A. The subscription filter is set to exclude all messages

B. The topic does not exist

C. The subscription name is too long

D. The Service Bus namespace is in a different region

Solution

1. Step 1: Check subscription filters

   If a subscription filter excludes all messages, no messages will be received even if the topic and subscription exist.

2. Step 2: Evaluate other options

   The topic does not exist would prevent subscription creation; The subscription name is too long would cause an error; The Service Bus namespace is in a different region does not block message reception.

3. Final Answer:

   The subscription filter is set to exclude all messages -> Option A

4. Quick Check:

   Filter excluding messages = no messages received [OK]

Hint: Check subscription filters if no messages arrive [OK]

Common Mistakes:

• Ignoring filters when troubleshooting
• Assuming region mismatch blocks messages
• Overlooking subscription existence

5. You want to ensure high availability and ordered message processing in your Service Bus topic subscriptions. Which configuration should you apply?

hard

A. Use multiple topics instead of subscriptions

B. Disable partitioning and use duplicate detection only

C. Enable partitioning on the topic and use sessions on subscriptions

D. Enable auto-delete on subscriptions after 1 hour

Solution

1. Step 1: Understand partitioning and sessions

   Partitioning improves availability by spreading messages across nodes. Sessions enable ordered processing by grouping related messages.

2. Step 2: Evaluate other options

   Disabling partitioning reduces availability; multiple topics don't guarantee order; auto-delete removes subscriptions prematurely.

3. Final Answer:

   Enable partitioning on the topic and use sessions on subscriptions -> Option C

4. Quick Check:

   Partitioning + sessions = high availability + order [OK]

Hint: Use partitioning for availability and sessions for order [OK]

Common Mistakes:

• Confusing duplicate detection with ordering
• Thinking multiple topics replace subscriptions
• Setting auto-delete too aggressively