cargo-lambda deploy merges environment variables with --merge-env
Introduced 2026-02-15 · 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.
cargo lambda deploy --merge-env --env-var NEW_VAR=VALUE <function-name>cargo lambda deploy --merge-env --env-vars FOO=BAR,BAZ=QUX <function-name>cargo lambda deploy --merge-env --env-file <path> <function-name>WHY THIS HELPS
Deploy a function while preserving environment variables managed outside Cargo Lambda.
BEFORE THIS CHANGE
Without `--merge-env`, deployment overwrites existing remote environment variables with the variables specified in configuration.
REQUIREMENTS AND LIMITATIONS
- 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 <path>: 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.
FIRST-PARTY EVIDENCE
- https://github.com/cargo-lambda/cargo-lambda/releases/tag/v1.9.0
- https://github.com/cargo-lambda/cargo-lambda/pull/910
- https://github.com/cargo-lambda/cargo-lambda/blob/v1.9.0/docs/commands/deploy.md
Check the installed version and the source before using it. Entry JSON