queue-consumers.md

Queue Consumers with Azure Functions

Azure Functions is commonly used to implement elastic consumers that process messages from queues/topics. This maps directly to cloud design patterns such as:

• Competing Consumers (parallelism for throughput)
• Queue-Based Load Leveling (buffer spikes and smooth processing)

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Reference architecture

flowchart LR
  P[Producers] --> Q[Queue / Topic]
  Q --> F1[Function Instance 1]
  Q --> F2[Function Instance 2]
  Q --> F3[Function Instance 3]
  F1 --> Down[Downstream]
  F2 --> Down
  F3 --> Down

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Practical guidance (L200–L300)

• Scale: use multiple instances to increase throughput; tune concurrency carefully to protect downstream systems.
• Idempotency: design handlers for at-least-once delivery.
• Retries and poison messages: define a strategy (retry with backoff, then dead-letter/quarantine).
• Poison isolation: route failures to a dead-letter queue and alert.

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References

• Competing Consumers pattern: https://learn.microsoft.com/en-us/azure/architecture/patterns/competing-consumers
• Queue-Based Load Leveling pattern: https://learn.microsoft.com/en-us/azure/architecture/patterns/queue-based-load-leveling
• Cloud design patterns catalog: https://learn.microsoft.com/en-us/azure/architecture/patterns/
• Azure Functions documentation: https://learn.microsoft.com/en-us/azure/azure-functions/