cargo-lambda watch processes concurrent invocations
Introduced 2026-02-15 · score 0.98
HOW TO USE IT
When you need local Lambda requests processed simultaneously, run `cargo lambda watch --concurrency 5` to allow up to five function instances, spawned on demand. Instances poll a shared queue, remain warm, and each runs with `AWS_LAMBDA_MAX_CONCURRENCY=1`; the limit is global per function.
cargo lambda watch --concurrency 5WHY THIS HELPS
Run a local Lambda function with multiple requests handled simultaneously.
BEFORE THIS CHANGE
By default, `cargo lambda watch` processes Lambda invocations sequentially with a single function instance.
REQUIREMENTS AND LIMITATIONS
- Version: v1.9.0
- --concurrency <maximum instances>: Sets the maximum number of function instances; instances are spawned dynamically based on demand. The documentation example uses `5`.
- Prerequisite: Run `cargo lambda watch` at the root of a Rust workspace.
- Concurrency is limited globally per function.
- Each instance runs in single-worker mode with `AWS_LAMBDA_MAX_CONCURRENCY=1`.
FIRST-PARTY EVIDENCE
- https://github.com/cargo-lambda/cargo-lambda/releases/tag/v1.9.0
- https://github.com/cargo-lambda/cargo-lambda/pull/921
- https://github.com/cargo-lambda/cargo-lambda/blob/v1.9.0/docs/commands/watch.md
Check the installed version and the source before using it. Entry JSON