Service Bus: Sessions, Dead-Lettering, and Duplicate Detection

Azure Service Bus provides several advanced features that go beyond basic send-and-receive. Sessions enable ordered, grouped message processing. Dead-lettering ensures that problematic messages are not lost. Duplicate detection prevents the same message from being processed twice. This lesson explores each of these features in depth and explains when to use them.

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Sessions

By default, messages in a Service Bus queue or subscription are delivered in FIFO order, but with competing consumers, multiple messages can be processed in parallel — meaning the overall processing order is not guaranteed.

Sessions solve this by grouping related messages and ensuring that all messages within a session are processed sequentially by a single consumer.

How Sessions Work

1. Each message is assigned a sessionId — a string that identifies the group
2. The queue or subscription must have sessions enabled at creation time
3. A consumer accepts a session and receives a lock on all messages with that session ID
4. Only one consumer can process a given session at a time
5. Different sessions can be processed in parallel by different consumers