Faster/Greener/Cheaper
Lambda functions with Rust

🏃 🌱 🤑 🐑 🦀

Luciano Mammino (@loige)

loige.link/be-a-crab

2024-09-06

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What is RUST?

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What is RUST?

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OK... Why do I like RUST?

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Why do I like Rust? ❤️

Zero-cost abstractions
Strongly typed with a really good type-system
Takes inspiration from Haskell, C++, OCaml, JavaScript, Ruby
Great (built-in) package manager (Cargo)
Great ecosystem of libraries
Pattern matching, no null, Option & Result types

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BTW, I am not the only one who likes Rust... 😏

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allthingsdistributed.com/2024/06/introducing-distill-cli.html

Let's sink our teeth

into some rusty goodness!

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use std::env;

fn main() {
    let region = env::var("AWS_REGION");
}

Result<String, VarError>

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😀 Happy path

🥺 Sad path

use std::env;

fn main() {
    let region = env::var("AWS_REGION");
    
    match region {
        Ok(region) => println!("Selected region: {}", region),
        Err(_) => println!("Error: AWS_REGION not set"),
    }
}

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😀 Happy path

🥺 Sad path

use std::env;

fn main() {
    let region = env::var("AWS_REGION")
        .expect("AWS_REGION environment variable not set");
}

String

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If you cannot get the value, panic!

use std::env;

fn main() {
    let region = env::var("AWS_REGION")
        .unwrap_or_else(|_| "eu-west-1".to_string());
}

Rust makes it very hard for you to ignore possible errors or the absence of values.

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if you cannot get the value, use a default value!

Why RUST + Lambda?

Why Rust + Lambda

Performance + Efficient memory-wise = COST SAVING 🤑
Very fast cold starts! (proof) ⚡️
Multi-thread safety 💪
No null types + Great error primitives = fewer bugs 🐞

𝕏 loige

👋 I'm Luciano (🇮🇹🍕🍝🤌)

👨‍💻 Senior Architect @ fourTheorem

nodejsdp.link

📔 Co-Author of Node.js Design Patterns 👉

Let's connect!

linktr.ee/loige

$ ~ whoami

Always re-imagining

We are a pioneering technology consultancy focused on AWS and serverless

✉️ Reach out to us at hello@fourTheorem.com

😇 We are always looking for talent: fth.link/careers

We can help with:

Cloud Migrations

Training & Cloud enablement

Building high-performance serverless applications

Cutting cloud costs

𝕏 loige

awsbites.com

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Where do we start?

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Let's try to create a new function

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RUST?!

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RUST?!

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EASY PEASY... we just need a custom runtime! 🤗

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🏃‍♂️ Lambda execution model

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🏃‍♂️ Lambda execution model

Runtime

Handler (logic)

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🏃‍♂️ Lambda execution model

Runtime

Handler (logic)

Poll for events

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🏃‍♂️ Lambda execution model

Runtime

Handler (logic)

Poll for events

event (JSON)

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🏃‍♂️ Lambda execution model

Runtime

Handler (logic)

Poll for events

event (JSON)

execute

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🏃‍♂️ Lambda execution model

Runtime

Handler (logic)

Poll for events

event (JSON)

execute

response or
error

𝕏 loige

🏃‍♂️ Lambda execution model

Runtime

Handler (logic)

Poll for events

event (JSON)

execute

response or
error

response (JSON)
or error

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Load the handler code

Infinite loop

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AWS made a Custom Rust Runtime for Lambda!

github.com/awslabs/aws-lambda-rust-runtime

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OK, Where do we start?

install Rust

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rustup.rs

What
next?

install cargo-lambda

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cargo-lambda.info

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use aws_lambda_events::event::s3::S3Event;
use lambda_runtime::{run, service_fn, Error, LambdaEvent};

async fn function_handler(event: LambdaEvent<S3Event>) -> Result<(), Error> {
    for record in event.payload.records {
        tracing::info!(
            "[{}] Bucket={} Key={}",
            record.event_name.unwrap_or_default(),
            record.s3.bucket.name.unwrap_or_default(),
            record.s3.object.key.unwrap_or_default()
        );
    }
    Ok(())
}

#[tokio::main]
async fn main() -> Result<(), Error> {
    tracing::init_default_subscriber();

    run(service_fn(function_handler)).await
}

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Request & Response types

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async fn function_handler(event: LambdaEvent<S3Event>) 
  -> Result<(), Error> {
    // ...
    Ok(())
}

Request

Response

What if we want to use different types? 🤨

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Option 1

use type definitions in the aws_lambda_events crate

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Processing jobs from SQS

Example

Jobs

Event source mapper

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# Cargo.toml

[dependencies]
aws_lambda_events = { 
  version = "0.15.0",
  default-features = false,
  features = [
    "sqs",
  ]
}

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use aws_lambda_events::event::sqs::{BatchItemFailure, SqsBatchResponse, SqsEvent};
// ...

async fn function_handler(event: LambdaEvent<SqsEvent>)
  -> Result<SqsBatchResponse, Error> {
    let mut failed_jobs = Vec::with_capacity(event.payload.records.len());

    for record in event.payload.records {
        // process the job
        // ...
        // if the job failed, add it to the failed_jobs list
        failed_jobs.push(BatchItemFailure {
            item_identifier: record.message_id.unwrap_or_default(),
        });
    }

    Ok(SqsBatchResponse {
        batch_item_failures: failed_jobs,
    })
}

// ...

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Option 2

Create custom request and response types

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Custom logic in Step Function

Example

loige.link/fsb-refactor

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# Cargo.toml

[dependencies]
serde = "1.0.200"
serde_json = "1.0.116"

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// ...

#[derive(serde::Deserialize)]
struct Request {
    url: String,
}

#[derive(serde::Serialize)]
struct Response {
    issue_number: u32,
}

async fn function_handler(event: LambdaEvent<Request>) 
  -> Result<Response, Error> {
    println!("I am going to scrape {}", event.payload.url);
    // TODO: actual scraping logic here
    Ok(Response { issue_number: 333 })
}

// ...

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Option 3

Use arbitrary JSON values!

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// ...

async fn function_handler(
    event: LambdaEvent<serde_json::Value>,
) -> Result<serde_json::Value, Error> {
    let url = event
        .payload
        .as_object()
        .unwrap()
        .get("url")
        .unwrap()
        .as_str()
        .unwrap(); // 🤮
    println!("I am going to scrape {}", url);
    // TODO: actual scraping logic here
    Ok(serde_json::json!({ "issue_number": 333 }))
}

// ...

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HTTP-based lambdas

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use lambda_http::{run, service_fn, Body, Error, Request, RequestExt, Response};

async fn function_handler(event: Request) -> Result<Response<Body>, Error> {
    // Extract some useful information from the request
    let who = event
        .query_string_parameters_ref()
        .and_then(|params| params.first("name"))
        .unwrap_or("world");
    
    let message = format!("Hello {who}, this is an AWS Lambda HTTP request");

    // Return something that implements IntoResponse.
    // It will be serialized to the right response event 
    // automatically by the runtime
    let resp = Response::builder()
        .status(200)
        .header("content-type", "text/html")
        .body(message.into())
        .map_err(Box::new)?;
    Ok(resp)
}

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use lambda_http::{run, service_fn, Body, Error, Request, RequestExt, Response};

async fn function_handler(event: Request) -> Result<Response<Body>, Error> {
    // Extract some useful information from the request
    let who = event
        .query_string_parameters_ref()
        .and_then(|params| params.first("name"))
        .unwrap_or("world");
    
    let message = format!("Hello {who}, this is an AWS Lambda HTTP request");

    // Return something that implements IntoResponse.
    // It will be serialized to the right response event 
    // automatically by the runtime
    let resp = Response::builder()
        .status(200)
        .header("content-type", "text/html")
        .body(message.into())
        .map_err(Box::new)?;
    Ok(resp)
}

These are just abstractions! 🧐

Lambda is still using JSON behind the scenes.

For HTTP you generally use the Lambda-Proxy integration.

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Building & Deploying

cargo lambda build --release && cargo lambda deploy

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loige

NO TRIGGER CONFIGURED! 🙄

WUT!? 😱

loige

🔥 HOT TIP

cargo lambda deploy --enable-function-url

SAM

Serverless Application Model

IaC with...

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AWS SAM + Cargo Lambda

SAM Works with Cargo Lambda (beta feature):

Define IaC with the full power of SAM
Build and run your Rust lambdas with Cargo Lambda
Can simulate API Gateway locally!

Note: Cargo Lambda also works with CDK
(github.com/cargo-lambda/cargo-lambda-cdk)

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# template.yaml

AWSTemplateFormatVersion: "2010-09-09"
Transform:
  - AWS::Serverless-2016-10-31

Resources:
  ExampleHttpLambda:
    Type: AWS::Serverless::Function
    Metadata:
      BuildMethod: rust-cargolambda
    Properties:
      CodeUri: .
      Handler: bootstrap
      Runtime: provided.al2023
      Architectures:
        - arm64
      Events:
        HttpPost:
          Type: Api
          Properties:
            Path: /
            Method: get

# samconfig.toml

version = 0.1

[default]
[default.global]
[default.global.parameters]
stack_name = "rust-http-lambda"

[default.build.parameters]
beta_features = true
[default.sync.parameters]
beta_features = true

Tells SAM to build using Cargo Lambda

Selects a "custom runtime"

Defines an HTTP trigger
(API Gateway)

Enables SAM beta features

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Building, Local testing & Deploying

sam build
sam local start-api
sam deploy

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Closing notes

Lambda is great (but you knew that already 😉)
Writing Lambdas in Rust is fun and it can be very cost-efficient
Still not very common to write Lambdas in Rust, but the tooling and the DX is already quite good (Cargo Lambda + SAM / CDK)
Go, have fun, share your learnings!