Compare Event Hubs and Service Bus for an ingestion workload

You are designing an ingestion workload and need to decide between Azure Event Hubs and Azure Service Bus. The choice depends on whether your data represents high-volume telemetry streams or discrete business messages requiring strict ordering and transactional integrity.

Event Hubs is a big data streaming platform designed to receive and process millions of events per second. It facilitates the capture, retention, and replay of telemetry and event stream data. Service Bus is a fully managed enterprise message broker intended for applications that require transactions, ordering, duplicate detection, and strong durability. Using Event Hubs for order processing or Service Bus for telemetry ingestion introduces unnecessary complexity or performance bottlenecks.

Understand the data: Events versus Messages

The first step is to classify the data you are ingesting. Azure messaging services distinguish between events and messages, and this distinction drives the architecture.

An event is a lightweight notification of a condition or a state change. The publisher has no expectation about how the event is handled. For example, an event might notify consumers that a file was created. It contains information about what happened but not the file itself. Events are ideal for serverless solutions and reactive programming. A series of events reports a condition and is analyzable. The events are time-ordered and interrelated, and the consumer needs the sequenced series to analyze what happened.

A message is raw data produced by a service to be consumed or stored elsewhere. The message contains the data that triggered the pipeline. The publisher has an expectation about how the consumer handles the message. A contract exists between the two sides. For example, the publisher sends a message with raw data and expects the consumer to create a file from that data and send a response. Messages are used for high-value enterprise messaging that cannot be lost or duplicated.

If your ingestion workload involves telemetry, clickstream data, or IoT sensor readings, you are dealing with a series of events. If your workload involves sales orders, financial transactions, or inventory movements, you are dealing with messages.

Evaluate throughput and scale

Event Hubs is built for volume. It can receive and process millions of events per second with low latency. It is designed for big data pipelines where the primary constraint is ingestion speed and the ability to retain data for replay. Event Hubs provides at least once delivery of an event. It does not guarantee global ordering across partitions. You must manage ordering within partitions.

Service Bus is built for reliability and control. It provides reliable asynchronous message delivery using a pull-based model. If you need to receive messages without busy-polling, you can use long polling receive operations using TCP-based protocols. Service Bus supports advanced features like first-in, first-out (FIFO), batching, sessions, transactions, dead-lettering, temporal control, routing, filtering, and duplicate detection. It provides at least once delivery of a message and optional ordered delivery.

If your ingestion workload requires processing millions of events per second, Event Hubs is the appropriate choice. If your workload involves a lower volume of high-value messages that require strict ordering, transactions, or duplicate detection, Service Bus is the better fit.

Consider delivery semantics and ordering

Event Hubs offers at least once delivery. This means that events might be delivered more than once, and duplicates are possible. If your downstream processing is idempotent, this is acceptable. Event Hubs does not guarantee global ordering across partitions. You must manage ordering within partitions.

Service Bus also offers at least once delivery but provides optional ordered delivery through message sessions. Sessions enable first-in, first-out (FIFO) guarantees for processing messages in Service Bus queues or subscriptions. This is critical for business processes where the order of operations matters, such as order processing. Service Bus also supports transactions, allowing you to group operations into an atomic scope. For example, you can obtain a message from one queue, post results to another, and move the input message, all within a single transaction. The results become visible to downstream consumers only upon success.

If your ingestion workload requires strict ordering and transactional integrity, Service Bus is the correct choice. If your workload can tolerate duplicates and does not require global ordering, Event Hubs is sufficient.

Plan for governance and throttling

Event Hubs provides resource governance through application groups, available only in Premium and Dedicated tiers. An application group is a logical collection of client applications that interact with the Event Hubs data plane. You can apply quota and access management policies, such as throttling policies, to control ingress and egress workloads. Throttling policies can limit incoming bytes, outgoing bytes, incoming messages, and outgoing messages per second. This is useful for governing event streaming workloads of client applications.

Service Bus manages throughput via namespace tiers and standard Azure resource limits. It does not have an equivalent to application groups. Service Bus provides advanced features like dead-letter queues for messages that cannot be processed, scheduled delivery for delayed processing, and message deferral for temporary holds. These features are useful for enterprise messaging scenarios where messages might need to be retried or held for later processing.

If you need fine-grained control over client application throughput at the data plane, Event Hubs application groups are a valuable tool. If you need advanced message lifecycle management, Service Bus provides the necessary features.

Make the decision

Use Event Hubs for telemetry and distributed data streaming. It is a big data pipeline that facilitates rapid data retrieval for real-time processing and repeated replay of stored raw data. It is ideal for scenarios where you need to capture streaming data into a file for processing and analysis.

Use Service Bus for order processing and financial transactions. It is an enterprise message broker that enables cloud-native applications to provide reliable state transition management for business processes. It is ideal for scenarios where you need to safely route and transfer data and control across service and application boundaries, and coordinate transactional work that requires a high degree of reliability.

In some cases, you might use both services side by side. For example, an e-commerce site can use Service Bus to process the order, Event Hubs to capture site telemetry, and Event Grid to respond to events like an item was shipped. However, for a single ingestion workload, choose the service that matches the nature of your data.

To verify your choice, assess your throughput requirements and your ordering constraints. If you need millions of events per second and can handle duplicates, choose Event Hubs. If you need strict ordering, transactions, and duplicate detection for high-value messages, choose Service Bus.

Related content

• Asynchronous messaging options in Azure
• Events, Data Points, and Messages - Choosing the right Azure messaging service for your data

References for Compare Event Hubs and Service Bus for an ingestion workload: Compare Azure messaging services, Resource governance with application groups, Introduction to Azure Service Bus.