Fan-out/fan-in refers to the pattern of executing multiple units of work in parallel and then synchronizing on their completion. While it’s often discussed in the context of serverless functions, the concept is not limited to them.
More generally, fan-out/fan-in describes a concurrency pattern that can be applied wherever tasks can be decomposed into independent pieces—such as threads, processes, actors, microservices, or even distributed jobs—executed concurrently and later aggregated into a single result. The key idea is the separation of work into parallel branches (fan-out) and the coordinated collection of their outputs (fan-in), regardless of the underlying execution model or infrastructure.
Fan-out and Fan-in Design Pattern
In practical engineering, the fan-out / fan-in pattern is commonly used to improve system throughput and resource utilization, especially in I/O-bound or highly parallelizable scenarios. By decomposing a complex task into multiple independent subtasks and executing them concurrently, the overall processing time can be significantly reduced. During the fan-in phase, the results of these subtasks are aggregated, ordered, or merged in a unified manner, helping to preserve the integrity and consistency of the business logic. However, this pattern also requires careful attention to concurrency control, error handling, as well as timeout and retry mechanisms; otherwise, high levels of parallelism may introduce resource contention, cascading failures, or inconsistent results. Therefore, when designing and implementing a fan-out / fan-in architecture, it is important to balance the degree of concurrency against system complexity and overall stability.
System Design
330 wordsLast Post: ChatGPT: New Image Creation (art school)