Fan-Out - CI/CD Glossary Definition
Fan-out spreads one unit of CI work across many parallel jobs to cut wall-clock time.
Fan-out is splitting one CI job into many parallel jobs so independent work (test shards, matrix combinations, per-package builds) runs at the same time instead of serially.
Fan-out is a scheduling shape where a pipeline expands a single logical stage into many concurrent jobs. In GitHub Actions it is commonly expressed with strategy.matrix or by generating jobs dynamically.
How it works
A coordinator step produces a list of work items (shards, versions, packages) and downstream jobs run one item each in parallel. Throughput is bounded by your available runner concurrency.
In CI
Fan-out is the fastest way to shorten a long test suite, but it multiplies runner minutes. Balance shard count against concurrency limits so jobs do not queue.