Service Bus FAQ
This article answers some frequently-asked questions about Microsoft Azure Service Bus. You can also visit the Azure Support FAQ for general Azure pricing and support information. The following topics are included:
- General questions about Azure Service Bus messaging
- Service Bus best practices
- Service Bus pricing
- Service Bus quotas
- Subscription and namespace management
Azure Service Bus messaging is an asynchronous messaging cloud platform that enables you to send data between decoupled systems. Microsoft offers this as a service, which means that you do not need to host any of your own hardware in order to use it.
A namespace provides a scoping container for addressing Service Bus resources within your application. Creating one is necessary to use Service Bus and will be one of the first steps in getting started.
A Service Bus queue is an entity in which messages are stored. Queues are particularly 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.
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.
The relay service provides the ability to transparently host and access WCF services from anywhere. In other words, this enables hybrid applications that run in both an Azure datacenter and an on-premises enterprise environment.
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 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. In addition, a temporary outage of a messaging store does not render a partitioned queue or topic unavailable.
Please keep in mind that ordering is not ensured when using partitioning entities. In the event that a partition is unavailable, you can still send and receive messages from the other partitions.
Best practices for performance improvements using Service Bus brokered messaging – this article describes how to optimize performance when exchanging brokered messages.
Best practices for insulating applications against Service Bus outages and disasters – this article discusses how best to protect relay endpoints, queues and topics, and active and passive replication against datacenter outages.
The following properties of a queue and topic are immutable. Please take this into account when you provision your entities as this cannot be modified, without creating a new replacement entity.
This section answers some frequently-asked questions about the Service Bus pricing structure. You can also visit the Azure Support FAQ for general Microsoft Azure pricing information. For complete information about Service Bus pricing, see Service Bus pricing details.
For complete information about Service Bus pricing, please 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.
Any data transfer within a given Azure region is provided at no charge. Any data transfer outside a region is subject to egress charges at the rate of $0.15 per GB from the North America and Europe regions, and $0.20 per GB from the Asia-Pacific region. Any inbound data transfer is provided at no charge.
Relay hours are billed for the cumulative amount of time during which each Service Bus relay is "open" during a given billing period. A relay is implicitly instantiated and opened at a given Service Bus address (service namespace URL) when a relay-enabled WCF service, or "Relay listener," first connects to that address. The relay is closed only when the last listener disconnects from its address. Therefore, for billing purposes a relay is considered "open" from the time the first relay listener connects, to the time the last relay listener disconnects from the Service Bus address of that relay. In other words, a relay is considered open whenever one or more relay listeners are connected to its Service Bus address.
In some cases, a single relay in Service Bus may have multiple connected listeners. This can occur with load-balanced services that use the netTCPRelay or HttpRelay WCF bindings, or with broadcast event listeners that use the netEventRelay WCF binding. A relay in Service Bus is considered "open" when at least one relay listener is connected to it. Adding additional listeners to an open relay does not change the status of that relay for billing purposes. The number of relay senders (clients that invoke or send messages to relays) connected to a relay also has no effect on the calculation of relay hours.
In general, billable messages are calculated for relays using the same method as described above for brokered entities (queues, topics, and subscriptions). However, there are several notable differences:
Sending a message to a Service Bus relay is treated as a "full through" send to the relay listener that receives the message, rather than a send to the Service Bus relay followed by a delivery to the relay listener. Therefore, a request-reply style service invocation (of up to 64 KB) against a relay listener will result in two billable messages: one billable message for the request and one billable message for the response (assuming the response is also <= 64 KB). This differs from using a queue to mediate between a client and a service. In the latter case, the same request-reply pattern would require a request send to the queue, followed by a dequeue/delivery from the queue to the service, followed by a response send to another queue, and a dequeue/delivery from that queue to the client. Using the same (<= 64 KB) size assumptions throughout, the mediated queue pattern would thus result in four billable messages, twice the number billed to implement the same pattern using relay. Of course, there are benefits to using queues to achieve this pattern, such as durability and load leveling. These benefits may justify the additional expense.
Relays that are opened using the netTCPRelay WCF binding treat messages not as individual messages but as a stream of data flowing through the system. In other words, only the sender and listener have visibility into the framing of the individual messages sent/received using this binding. Thus, for relays using the netTCPRelay bindng, all data is treated as a stream for the purpose of calculating billable messages. In this case, Service Bus will calculate the total amount of data sent or received via each individual relay on a 5-minute basis and divide that total by 64 KB in order to determine the number of billable messages for the relay in question during that time period.
No, Service Bus does not charge for storage. However, there is a quota limiting the maximum amount of data that can be persisted per queue/topic. See the next FAQ.
For a list of Service Bus limits and quotas, see Quotas overview.
By default, for any cloud service Microsoft sets an aggregate monthly usage quota that is calculated across all of a customer's subscriptions. Because we understand that you may need more than these limits, please contact customer service at any time so that we can understand your needs and adjust these limits appropriately. For Service Bus, the aggregate usage quotas are as follows:
- 5 billion messages
- 2 million relay hours
While we do reserve the right to disable a customer account that has exceeded its usage quotas in a given month, we will provide e-mail notification and make multiple attempts to contact a customer before taking any action. Customers exceeding these quotas will still be responsible for charges that exceed the quotas.
As with other services on Azure, Service Bus enforces a set of specific quotas to ensure that there is fair usage of resources. The following are the usage quotas that the service enforces:
You specify the maximum queue or topic size upon creation of the queue or topic. This quota can have a value of 1, 2, 3, 4, or 5 GB. If the maximum size is reached, additional incoming messages will be rejected and an exception will be received by the calling code.
Queue/Topic/Subscription - The number of concurrent TCP connections on a queue/topic/subscription is limited to 100. If this quota is reached, subsequent requests for additional connections will be rejected and an exception will be received by the calling code. For every messaging factory, Service Bus maintains one TCP connection if any of the clients created by that messaging factory have an active operation pending, or have completed an operation less than 60 seconds ago. REST operations do not count towards concurrent TCP connections.
The number of concurrent netTcpRelay and netHttpRelay listeners on a relay is limited to 25 (1 for a NetOneway relay).
Service Bus enforces a limit of 2000 concurrent relay listeners per service namespace. If this quota is reached, subsequent requests to open additional relay listeners will be rejected and an exception will be received by the calling code.
The maximum number of topics/queues (durable storage-backed entities) on a service namespace is limited to 10,000. If this quota is reached, subsequent requests for creation of a new topic/queue on the service namespace will be rejected. In this case, the Azure classic portal will display an error message or the calling client code will receive an exception, depending on whether the create attempt was done via the portal or in client code.
Message size – Each message is limited to a total size of 256KB, including message headers.
Message header size – Each message header is limited to 64KB.
NetOneway and NetEvent relays - Each message is limited to a total size of 64KB, including message headers.
Http and NetTcp relays – Service Bus does not enforce an upper bound on the size of these messages.
Messages that exceed these size quotas will be rejected and an exception will be received by the calling code.
Number of subscriptions per topic – The maximum number of subscriptions per topic is limited to 2,000. If this quota is reached, subsequent requests for creating additional subscriptions to the topic will be rejected. In this case, the Azure classic portal will display an error message or the calling client code will receive an exception, depending on whether the create attempt was done via the portal or in client code.
Number of SQL filters per topic – The maximum number of SQL filters per topic is limited to 2,000. If this quota is reached, any subsequent requests for creation of additional filters on the topic will be rejected and an exception will be received by the calling code.
Number of correlation filters per topic – The maximum number of correlation filters per topic is limited to 100,000. If this quota is reached, any subsequent requests for creation of additional filters on the topic will be rejected and an exception will be received by the calling code.
You can use PowerShell commands (found in the article here) to move a namespace from one Azure subscription to another. In order to execute the operation, the namespace must already be active. Also the user executing the commands must be an administrator on both source and target subscriptions.
What are some of the exceptions generated by Azure Service Bus messaging APIs and their suggested actions?
The exceptions that messaging APIs can generate fall into the following categories:
User coding error
The Service Bus messaging exceptions article describes some exceptions with suggested actions.
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, PHP, Java and C#, see the Shared Access Signatures article.
To learn more about Service Bus messaging, see the following topics.