Idempotent Consumer

Kind: pattern

Layer: Execution Core

Record: architecture:idempotent-consumer

Severity: contextual

Scope: service, messaging, correctness

Canonical: Ontology

A design pattern in which a consumer records each message it has processed, so a redelivered message has no second effect.

Listed in Architecture principles, after Dead-Letter Queue and before Competing Consumers.

Requires

• Deduplication Key

Reinforces

• Eventual Consistency
• At-Least-Once Delivery Safety

Enables

• Safe Message Redelivery

Conflicts with

• Duplicate Side Effects

In tension with

• State Overhead

Tensions

• Idempotent Consumer / State Overhead

Violated by

• Duplicate Side Effects

Severity

• contextual

Category

• Event / Messaging / Asynchronous Architecture

Refactors

• Dual Write
• Idempotency

Linked from

• Posting and waiting are one operation
• Anti-patterns
• Event / Messaging / Asynchronous Architecture
• Transactions / State / Concurrency
• Event Messaging Async
• Severity levels
• The resolutions