Rust HTTP Lambda

Building and Deploying

The easiest way to start writing Lambda functions with Rust is by using Cargo Lambda, a project related to the aws-rust-lambda-runtime project. Cargo Lambda is a Cargo plugin, or subcommand, that provides several commands to help you in your journey with Rust on AWS Lambda.

The preferred way to install Cargo Lambda is by using a package manager.

Use Homebrew on MacOS:

brew tap cargo-lambda/cargo-lambda
brew install cargo-lambda

Use Scoop on Windows:

scoop bucket add cargo-lambda https://github.com/cargo-lambda/scoop-cargo-lambda
scoop install cargo-lambda/cargo-lambda

Or PiP on any system with Python 3 installed:

pip3 install cargo-lambda

Zig!

Cargo Lambda is written in Zig, which I was able to install and get things working using asdf.

Building for Amazon Linux 2

This function was created using the command cargo lambda new rust-http-lambda.

It is recommended to use Amazon Linux 2 runtimes (such as provided.al2) as much as possible for building Lambda functions in Rust. To build your Lambda functions for Amazon Linux 2 runtimes, from inside the rust-http-lambda module, run:

cargo lambda build --release --arm64

There are other ways of building your function: manually with the AWS CLI, with AWS SAM, and with the Serverless framework.

Deploying to AWS Lambda

For a custom runtime, AWS Lambda looks for an executable called bootstrap in the deployment package zip. Rename the generated executable to bootstrap and add it to a zip archive.

You can find the bootstrap binary for your function under the target/lambda directory.

Deploying with Cargo Lambda

Use the deploy subcommand to upload your function to AWS:

cargo lambda deploy \
  --enable-function-url \
  --iam-role arn:aws:iam::XXXXXXXXXXXXX:role/your_lambda_execution_role
  --tags team=hewmen \
  rust-http-lambda

This command will create a Lambda function with the same name of your rust package.

Make sure to replace the execution role with an existing role in your account!

See other deployment options in the Cargo Lambda documentation.

Lambda Execution Role

If you run the cargo lambda deploy command without any flags, Cargo Lambda will try to create an execution role with Lambda's default service role policy AWSLambdaBasicExecutionRole.

The AWSLambdaBasicExecutionRole contains the following permissions:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "logs:CreateLogGroup",
                "logs:CreateLogStream",
                "logs:PutLogEvents"
            ],
            "Resource": "*"
        }
    ]
}

Invoking

You can test the function with the invoke subcommand:

cargo lambda invoke --remote \
  --data-ascii '{"command": "hi"}' \
  --output-format json \
  my-first-lambda-function

Deploying with the AWS CLI

You can also use the AWS CLI to deploy your Rust functions. First, you will need to create a ZIP archive of your function. Cargo Lambda can do that for you automatically when it builds your binary if you add the output-format flag:

cargo lambda build --release --arm64 --output-format zip

You can find the resulting zip file in target/lambda/YOUR_PACKAGE/bootstrap.zip. Use that file path to deploy your function with the AWS CLI:

$ aws lambda create-function --function-name rustTest \
  --handler bootstrap \
  --zip-file fileb://./target/lambda/basic/bootstrap.zip \
  --runtime provided.al2023 \ # Change this to provided.al2 if you would like to use Amazon Linux 2 (or to provided.al for Amazon Linux 1).
  --role arn:aws:iam::XXXXXXXXXXXXX:role/your_lambda_execution_role \
  --environment Variables={RUST_BACKTRACE=1} \
  --tracing-config Mode=Active