Azure Service Bus - Frequently asked questions (FAQ)

This article discusses some frequently asked questions about Microsoft Azure Service Bus. You can also visit the Azure Support FAQs for general Azure pricing and support information.

General questions about Azure Service Bus

What is Azure Service Bus?

Azure Service Bus is an asynchronous messaging cloud platform that enables you to send data between decoupled systems. Microsoft offers this feature as a service, which means that you don't need to host your own hardware to use it.

What is a Service Bus namespace?

A namespace provides a scoping container for addressing Service Bus resources within your application. Creating a namespace is necessary to use Service Bus and is one of the first steps in getting started.

What is an Azure Service Bus queue?

A Service Bus queue is an entity in which messages are stored. Queues are useful when you have multiple applications, or multiple parts of a distributed application that need to communicate with each other. The queue is similar to a distribution center in that multiple products (messages) are received and then sent from that location.

What are Azure Service Bus topics and subscriptions?

A topic can be visualized as a queue and when using multiple subscriptions, it becomes a richer messaging model; essentially a one-to-many communication tool. This publish/subscribe model (or pub/sub) enables an application that sends a message to a topic with multiple subscriptions to have that message received by multiple applications.

What is a partitioned entity?

A conventional queue or topic is handled by a single message broker and stored in one messaging store. A partitioned queue, or topic is handled by multiple message brokers and stored in multiple messaging stores. This feature means that the overall throughput of a partitioned queue or topic is no longer limited by the performance of a single message broker or messaging store. Also, a temporary outage of a messaging store doesn't render a partitioned queue or topic unavailable.

Ordering isn't ensured when using partitioned entities. In the event that a partition is unavailable, you can still send and receive messages from the other partitions.

Where does Azure Service Bus store data?

Azure Service Bus standard tier utilizes Azure SQL Database for its backend storage layer. For all regions except Brazil South and Southeast Asia, the database backup is hosted in a different region (usually the Azure paired region). For the Brazil south and Southeast Asia regions, database backups are stored in the same region to accommodate data-residency requirements for these regions.

Azure Service Bus premium tier stores metadata and data in regions that you select. When geo-disaster recovery is set up for an Azure Service Bus premium namespace, the metadata is copied over to the secondary region that you select.

What ports do I need to open on the firewall?

You can use the following protocols with Azure Service Bus to send and receive messages:

  • Advanced Message Queuing Protocol 1.0 (AMQP)
  • Hypertext Transfer Protocol 1.1 with TLS (HTTPS)

See the following table for the outbound TCP ports you need to open to use these protocols to communicate with Azure Service Bus:

Protocol Ports Details
AMQP 5671, 5672 AMQP with TLS. See AMQP protocol guide
HTTPS 443 This port is used for the HTTP/REST API and for AMQP-over-WebSockets

The HTTPS port is generally required for outbound communication also when AMQP is used over port 5671, because several management operations performed by the client SDKs and the acquisition of tokens from Azure Active Directory (when used) run over HTTPS.

The official Azure SDKs generally use the AMQP protocol for sending and receiving messages from Service Bus.

The AMQP-over-WebSockets protocol option runs over port TCP 443 just like the HTTP/REST API, but is otherwise functionally identical with plain AMQP. This option has higher initial connection latency because of extra handshake roundtrips and slightly more overhead as tradeoff for sharing the HTTPS port. If this mode is selected, TCP port 443 is sufficient for communication. The following options allow selecting the AMQP WebSockets mode.

Language Option
.NET (Azure.Messaging.ServiceBus) Create ServiceBusClient using a constructor that takes ServiceBusClientOptions as a parameter. Set ServiceBusClientOptions.TransportType to ServiceBusTransportType.AmqpWebSockets
.NET (Microsoft.Azure.ServiceBus) When creating client objects, use constructors that take TransportType, ServiceBusConnection, or ServiceBusConnectionStringBuilder as parameters.

For the construction that takes transportType as a parameter, set the parameter to TransportType.AmqpWebSockets.

For the constructor that takes ServiceBusConnection as a parameter, set the ServiceBusConnection.TransportType to TransportType.AmqpWebSockets.

If you use ServiceBusConnectionStringBuilder, use constructors that give you an option to specify the transportType.

Java ( When creating clients, set ServiceBusClientBuilder.transportType to AmqpTransportType.AMQP.AMQP_WEB_SOCKETS
Java ( When creating clients, set transportType in to
JavaScript When creating Service Bus client objects, use the webSocketOptions property in ServiceBusClientOptions.
Python When creating Service Bus clients, set ServiceBusClient.transport_type to TransportType.AmqpOverWebSocket

What IP addresses do I need to add to allowlist?

To find the right IP addresses to add to allowlist for your connections, follow these steps:

  1. Run the following command from a command prompt:

    nslookup <YourNamespaceName>
  2. Note down the IP address returned in Non-authoritative answer.

If you use the zone redundancy for your namespace, you need to do a few additional steps:

  1. First, you run nslookup on the namespace.

    nslookup <yournamespace>
  2. Note down the name in the non-authoritative answer section, which is in one of the following formats:

  3. Run nslookup for each one with suffixes s1, s2, and s3 to get the IP addresses of all three instances running in three availability zones,


    The IP address returned by the nslookup command isn't a static IP address. However, it remains constant until the underlying deployment is deleted or moved to a different cluster.

Where can I find the IP address of the client sending/receiving messages to/from a namespace?

We don't log the IP addresses of clients sending or receiving messages to/from your namespace. Regenerate keys so that all existing clients will fail to authenticate and review Azure role-based access control (Azure RBAC)) settings to ensure that only allowed users or applications have access to the namespace.

If you're using a premium namespace, use IP filtering, virtual network service endpoints, and private endpoints to limit access to the namespace.

Best practices

What are some Azure Service Bus best practices?

See Best practices for performance improvements using Service Bus – this article describes how to optimize performance when exchanging messages.

What should I know before creating entities?

The following properties of a queue and topic are immutable. Consider this limitation when you provision your entities, as these properties can't be modified without creating a new replacement entity.

  • Partitioning
  • Sessions
  • Duplicate detection
  • Express entity


This section answers some frequently asked questions about the Service Bus pricing structure.

The Service Bus pricing and billing article explains the billing meters in Service Bus. For specific information about Service Bus pricing options, see Service Bus pricing details.

You can also visit the Azure Support FAQs for general Azure pricing information.

How do you charge for Service Bus?

For complete information about Service Bus pricing, see Service Bus pricing details. In addition to the prices noted, you are charged for associated data transfers for egress outside of the data center in which your application is provisioned.

What usage of Service Bus is subject to data transfer? What isn't?

Any data transfer within a given Azure region is provided at no charge, as well as any inbound data transfer. Data transfer outside a region is subject to egress charges, which can be found here.

Does Service Bus charge for storage?

No. Service Bus doesn't charge for storage. However, there's a quota limiting the maximum amount of data that can be persisted per queue/topic. See the next FAQ.

I have a Service Bus Standard namespace. Why do I see charges under resource group '$system'?

Azure Service Bus recently upgraded the billing components. Because of this change, if you have a Service Bus Standard namespace, you may see line items for the resource '/subscriptions/<azure_subscription_id>/resourceGroups/$system/providers/Microsoft.ServiceBus/namespaces/$system' under resource group '$system'.

These charges represent the base charge per Azure subscription that has provisioned a Service Bus Standard namespace.

It's important to note that these charges aren't new, that is, they existed in the previous billing model too. The only change is that they're now listed under '$system'. It's done because of constraints in the new billing system that groups subscription level charges, not tied to a specific resource, under the '$system' resource ID.


For a list of Service Bus limits and quotas, see the Service Bus quotas overview.

How to handle messages of size > 1 MB?

Service Bus messaging services (queues and topics/subscriptions) allow application to send messages of size up to 256 KB (standard tier) or 100 MB (premium tier). If you're dealing with messages of size greater than the allowed size, use the claim check pattern described in this blog post.


Why am I not able to create a namespace after deleting it from another subscription?

When you delete a namespace from a subscription, wait for 4 hours before recreating it with the same name in another subscription. Otherwise, you may receive the following error message: Namespace already exists.

What are some of the exceptions generated by Azure Service Bus APIs and their suggested actions?

For a list of possible Service Bus exceptions, see Exceptions overview.

What is a Shared Access Signature and which languages support generating a signature?

Shared Access Signatures are an authentication mechanism based on SHA-256 secure hashes or URIs. For information about how to generate your own signatures in Node.js, PHP, Java, Python, and C#, see the Shared Access Signatures article.

Subscription and namespace management

How do I migrate a namespace to another Azure subscription?

You can move a namespace from one Azure subscription to another, using either the Azure portal or PowerShell commands. To execute the operation, the namespace must already be active. The user executing the commands must be an administrator on both the source and target subscriptions.


To use the Azure portal to migrate Service Bus namespaces to another subscription, follow the directions here.


The following sequence of PowerShell commands moves a namespace from one Azure subscription to another. To execute this operation, the namespace must already be active, and the user running the PowerShell commands must be an administrator on both the source and target subscriptions.

# Create a new resource group in target subscription
Select-AzSubscription -SubscriptionId 'ffffffff-ffff-ffff-ffff-ffffffffffff'
New-AzResourceGroup -Name 'targetRG' -Location 'East US'

# Move namespace from source subscription to target subscription
Select-AzSubscription -SubscriptionId 'aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa'
$res = Find-AzResource -ResourceNameContains mynamespace -ResourceType 'Microsoft.ServiceBus/namespaces'
Move-AzResource -DestinationResourceGroupName 'targetRG' -DestinationSubscriptionId 'ffffffff-ffff-ffff-ffff-ffffffffffff' -ResourceId $res.ResourceId

Is it possible to disable TLS 1.0 or 1.1 on Service Bus namespaces?

Yes, you can disable TLS 1.0 or 1.1 on Service Bus namespaces by setting the minimum TLS version. For more information, see Enforce a minimum required version of Transport Layer Security (TLS) for requests to a Service Bus namespace.

Next steps

To learn more about Service Bus, see the following articles: