--- schema_version: 1 route: /t/cargo-lambda.md tool: "cargo-lambda" --- # sincecutoff.com /t/cargo-lambda — cargo-lambda - name: cargo-lambda - kind: cli - children: none - homepage: Changes to the tools coding agents drive, since a model's training cutoff, each linked to its first-party source. Check installed versions and limitations before acting; a cutoff date does not establish what a model knows. Original editorial content: [Apache 2.0](https://sincecutoff.com/v1/data-license.txt), by [0xPatrick](https://0xpatrick.dev). Preserve applicable license and [NOTICE](https://sincecutoff.com/notice.txt) attribution when redistributing. Third-party source text and examples retain their own rights. [License scope and attribution](https://sincecutoff.com/v1/license.json). To stay current, read the changes feed: [`/v1/changes.md?tool=cargo-lambda`](https://sincecutoff.com/v1/changes.md?tool=cargo-lambda) (or `.json`), adding `since=YYYY-MM-DD` for your training cutoff. Entries for registered children are included; the registry itself is `/v1/tools.json`. How to page and save your place: [llms.txt](https://sincecutoff.com/llms.txt). ### cargo-lambda build accepts environment variables (2026-02-15) - slug: cargo-lambda-build-accepts-environment-variables-7208f8303734 - score: 0.98 How to use it: When a build needs environment variables, pass them with `--env-var` or load them with `--env-file`; CLI values override metadata, and `--env-var` overrides `--env-file`. Examples: ``` cargo lambda build --env-var = ``` ``` cargo lambda build --env-file ``` ``` [package.metadata.lambda.build] env_var = ["="] env_file = "" ``` - why_it_matters: Build a project that needs configured environment variables during the cargo build process. - sources: , , - gotchas: "Version: v1.9.0"; "--env-var =: Sets environment variables for the cargo build process. Repeat the flag or give comma-separated pairs."; "--env-file : Loads environment variables from a file, one `KEY=VALUE` entry per line."; "env_var: Cargo metadata array of `KEY=VALUE` strings for build-time variables."; "env_file: Cargo metadata path to an environment file for the build."; "Environment files should contain one `KEY=VALUE` entry per line."; "The stated precedence is environment file, then command-line `--env-var`; CLI values override metadata." ### cargo-lambda deploy merges environment variables with --merge-env (2026-02-15) - slug: cargo-lambda-deploy-merges-environment-variables-with-merge-env-db814b348311 - score: 0.96 How to use it: When deploying a function and remote environment variables must be preserved, run `cargo lambda deploy --merge-env` with the function name and the environment variables to add or update. Existing remote variables remain; local values take precedence for duplicates. Examples: ``` cargo lambda deploy --merge-env --env-var NEW_VAR=VALUE ``` ``` cargo lambda deploy --merge-env --env-vars FOO=BAR,BAZ=QUX ``` ``` cargo lambda deploy --merge-env --env-file

``` - why_it_matters: Deploy a function while preserving environment variables managed outside Cargo Lambda. - before: Without `--merge-env`, deployment overwrites existing remote environment variables with the variables specified in configuration. - sources: , , - gotchas: "Version: v1.9.0"; "--merge-env: Preserve existing remote environment variables; variables in local configuration are added or updated, with local values taking precedence for duplicates."; "--env-var KEY=VALUE: Set environment variables using KEY=VALUE. May be repeated; docs say it overrides --env-vars and cannot be combined with it."; "--env-vars KEY=VALUE,...: Set environment variables from a comma-separated list. Cannot be combined with --env-var."; "--env-file : Read environment variables from a file with one KEY=VALUE per line."; "function-name (required): Function name argument for the deploy command."; "merge_env: Cargo.toml deploy metadata boolean; `true` enables merging and the default is `false`."; "Prerequisite: Build the function binary before deploying; deploy fails if it cannot find the binary."; "Prerequisite: AWS account permissions for Lambda operations including `lambda:GetFunction`, `lambda:CreateFunction`, and `lambda:UpdateFunctionCode`; an IAM execution role with Lambda privileges is also required."; "Merging is enabled by the `--merge-env` flag or `merge_env = true`; the configuration default is false."; "When a variable is specified remotely and in configuration, the local value takes precedence." ### cargo-lambda watch processes concurrent invocations (2026-02-15) - slug: cargo-lambda-watch-processes-concurrent-invocations-9c1c41b88c7f - 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. Examples: ``` cargo lambda watch --concurrency 5 ``` - why_it_matters: Run a local Lambda function with multiple requests handled simultaneously. - before: By default, `cargo lambda watch` processes Lambda invocations sequentially with a single function instance. - sources: , , - gotchas: "Version: v1.9.0"; "--concurrency : 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`."