Rust Runtime for AWS Lambda

This package makes it easy to run AWS Lambda Functions written in Rust. This workspace includes multiple crates:

• lambda-runtime-client is a client SDK for the Lambda Runtime APIs. You probably don't need to use this crate directly!
• lambda-runtime is a library that makes it easy to write Lambda functions in Rust.
• lambda-http is a library that makes it easy to write API Gateway proxy event focused Lambda functions in Rust.

Example function

The code below creates a simple function that receives an event with a greeting and name field and returns a GreetingResponse message for the given name and greeting. Notice: to run these examples, we require a minimum Rust version of 1.31.

use std::error::Error;

use lambda_runtime::{error::HandlerError, lambda, Context};
use log::{self, error};
use serde_derive::{Deserialize, Serialize};
use simple_error::bail;
use simple_logger;

#[derive(Deserialize)]
struct CustomEvent {
    #[serde(rename = "firstName")]
    first_name: String,
}

#[derive(Serialize)]
struct CustomOutput {
    message: String,
}

fn main() -> Result<(), Box<dyn Error>> {
    simple_logger::init_with_level(log::Level::Debug)?;
    lambda!(my_handler);

    Ok(())
}

fn my_handler(e: CustomEvent, c: Context) -> Result<CustomOutput, HandlerError> {
    if e.first_name == "" {
        error!("Empty first name in request {}", c.aws_request_id);
        bail!("Empty first name");
    }

    Ok(CustomOutput {
        message: format!("Hello, {}!", e.first_name),
    })
}

The code above is the same as the basic example in the lambda-runtime crate.

Deployment

There are currently multiple ways of building this package: manually, and the Serverless framework.

To deploy the basic sample as a Lambda function using the AWS CLI, we first need to manually build it with cargo. Since Lambda uses Amazon Linux, you'll need to target your executable for an x86_64-linux platform.

$ cargo build -p lambda_runtime --example basic --release

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

$ cp ./target/release/examples/basic ./bootstrap && zip lambda.zip bootstrap && rm bootstrap

Now that we have a deployment package (lambda.zip), we can use the AWS CLI to create a new Lambda function. Make sure to replace the execution role with an existing role in your account!

$ aws lambda create-function --function-name rustTest \
  --handler doesnt.matter \
  --zip-file file://./lambda.zip \
  --runtime provided \
  --role arn:aws:iam::XXXXXXXXXXXXX:role/your_lambda_execution_role \
  --environment Variables={RUST_BACKTRACE=1} \
  --tracing-config Mode=Active

You can now test the function using the AWS CLI or the AWS Lambda console

$ aws lambda invoke --function-name rustTest \
  --payload '{"firstName": "world"}' \
  output.json
$ cat output.json  # Prints: {"message":"Hello, world!"}

Alternatively, you can build a Rust-based Lambda function declaratively using the Serverless framework Rust plugin.

A number of getting started Serverless application templates exist to get you up and running quickly

• a minimal echo function to demonstrate what the smallest Rust function setup looks like
• a minimal http function to demonstrate how to interface with API Gateway using Rust's native http crate (note this will be a git dependency until 0.2 is published)
• a combination multi function service to demonstrate how to set up a services with multiple independent functions

Assuming your host machine has a relatively recent version of node, you won't need to install any host-wide serverless dependencies. To get started, run the following commands to create a new lambda Rust application and install project level dependencies.

$ npx serverless install \
  --url https://github.com/softprops/serverless-aws-rust \
  --name my-new-app \
  && cd my-new-app \
  && npm install --silent

Deploy it using the standard serverless workflow

# build, package, and deploy service to aws lambda
$ npx serverless deploy

Invoke it using serverless framework or a configured AWS integrated trigger source:

$ npx serverless invoke -f hello -d '{"foo":"bar"}'

Alternatively, you can build a Rust-based Lambda function in a docker mirror of the AWS Lambda provided runtime with the Rust toolchain preinstalled.

Running the following command will start a ephemeral docker container which will build your Rust application and produce a zip file containing its binary auto-renamed to bootstrap to meet the AWS Lambda's expectations for binaries under target/lambda/release/{your-binary-name}.zip, typically this is just the name of your crate if you are using the cargo default binary (i.e. main.rs)

# build and package deploy-ready artifact
$ docker run --rm \
    -v ${PWD}:/code \
    -v ${HOME}/.cargo/registry:/root/.cargo/registry \
    -v ${HOME}/.cargo/git:/root/.cargo/git \
    softprops/lambda-rust

With your application build and packaged, it's ready to ship to production. You can also invoke it locally to verify is behavior using the lambdaci :provided docker container which is also a mirror of the AWS Lambda provided runtime with build dependencies omitted.

# start a docker container replicating the "provided" lambda runtime
# awaiting an event to be provided via stdin
$ unzip -o \
    target/lambda/release/{your-binary-name}.zip \
    -d /tmp/lambda && \
  docker run \
    -i -e DOCKER_LAMBDA_USE_STDIN=1 \
    --rm \
    -v /tmp/lambda:/var/task \
    lambci/lambda:provided

# provide an event payload via stdin (typically a json blob)

# Ctrl-D to yield control back to your function

lambda-runtime-client

Defines the RuntimeClient trait and provides its HttpRuntimeClient implementation. The client fetches events and returns output as Vec<u8>.

For error reporting to the runtime APIs the library defines the RuntimeApiError trait and the ErrorResponse object. Custom errors for the APIs should implement the to_response() -> ErrorResponse method of the RuntimeApiError trait.

lambda-runtime

This library makes it easy to create Rust executables for AWS lambda. The library defines a lambda!() macro. Call the lambda!() macro from your main method with an implementation the Handler type:

pub trait Handler<E, O> {
    /// Run the handler.
    fn run(
        &mut self,
        event: E,
        ctx: Context
    ) -> Result<O, HandlerError>;
}

Handler provides a default implementation that enables you to provide a Rust closure or function pointer to the lambda!() macro.

Optionally, you can pass your own instance of Tokio runtime to the lambda!() macro. See our with_custom_runtime.rs example

AWS event objects

This project does not currently include Lambda event struct definitions though we intend to do so in the future. Instead, the community-maintained aws_lambda_events crate can be leveraged to provide strongly-typed Lambda event structs. You can create your own custom event objects and their corresponding structs as well.

Custom event objects

To serialize and deserialize events and responses, we suggest using the use the serde library. To receive custom events, annotate your structure with Serde's macros:

extern crate serde;
extern crate serde_derive;
extern crate serde_json;

use serde_derive::{Serialize, Deserialize};
use serde_json::json;
use std::error::Error;

#[derive(Serialize, Deserialize)]
pub struct NewIceCreamEvent {
  pub flavors: Vec<String>,
}

#[derive(Serialize, Deserialize)]
pub struct NewIceCreamResponse {
  pub flavors_added_count: usize,
}

fn main() -> Result<(), Box<Error>> {
    let flavors = json!({
      "flavors": [
        "Nocciola",
        "抹茶",
        "आम"
      ]
    });

    let event: NewIceCreamEvent = serde_json::from_value(flavors)?;
    let response = NewIceCreamResponse {
        flavors_added_count: event.flavors.len(),
    };
    serde_json::to_string(&response)?;

    Ok(())
}