Simple Rust Lambda

Description

This is a simple AWS Lambda written in Rust that retrieves a file from an AWS S3 bucket and returns a random line from it.

Data flow

flowchart LR;
    client <--> api-gateway;
    api-gateway <--> lambda;
    lambda <--> s3;

Sequence

sequenceDiagram
    client ->> api-gateway:http-get
    api-gateway ->> lambda:http-post (invoke)
    lambda ->> s3:http-get (download file)
    s3 ->> lambda:ByteStream (file)
    lambda ->> lambda:get random line
    lambda ->> api-gateway:json response (line)
    api-gateway ->> client:json response (line)

I created this project to learn Rust with something more practical than typical "hello world!" example, and at the same time learn more about AWS in general. I use it to present inspriational/motivational messages on my blog - Leader Kaizen. It's simple enough to grapple with but complex enough that I could learn useful aspects of the language that I could apply to extend the function or develop more complex solutions.

It utilises Cargo Lambda which provides a set of tools for building Lambda's with Rust. It leverages the official lambda_runtime crate but it is considered a custom runtime as Rust is not natively supported by Lambda's yet.

This project contains:

Rust source for Lambda event function
AWS SAM template for deploying Lambda and API Gateway REST API
GitHub Actions to build the Lambda and deploy it and API using the SAM template

This project does not contain:

Bucket creation - I used an existing bucket
IAM user/role creation

This project assumes:

Rust is installed
AWS SAM CLI is installed and configured
AWS user account used has relevant permissions. Below are built in policies that work but I recommend building custom policies with least privileges appropriate for the use case:

AWSLambda_FullAccess
AWSCloudFormationFullAccess
AmazonS3FullAccess
AmazonAPIGatewayAdministrator

Arbitraty API usage plan and access using API key

Getting Started

Install Cargo Lambda
Based on your preferred shell, update env.ps1 or env.sh file with valid values (described here)

DO NOT COMMIT THESE FILES TO VERSION CONTROL. RECOMMEND ADDING TO .gitignore.

In a terminal, run:

cargo lambda watch
In another terminal, run:

cargo lambda invoke --data-ascii '{}'

Environment Variables

Key	Description
S3_KEY_ID	Key ID to access S3 bucket
S3_KEY_SECRET	Key secret to access S3 bucket
BUCKET	Bucket name
REGION	Bucket region
FILE_PATH	Full path to file, including filename and extension

Notes

Server runs on 127.0.0.1:9000
Full url for function: http://127.0.0.1:9000/lambda-url/simple-rust-lambda/
Because it is an event function is created so GET HTTP requests straight from the browser will fail - it is meant to be fronted by an API Gateway

Optional

Edit template.yml values as required (names, usage plan config, etc)
I calling from browser, update CORS values
If deploying using GitHub actions, create all keys and values in env files as secrets in the GitHub repo.

Build & Release

This project includes build and release workflows for GitHub Actions. Build and release are split into seperate workflows with build artifacts being cached so the deploy workflow can be re-run without needing to rebuild.

rust-cargo-build

flowchart TD;
    A(Install Homebrew) --> B(Install cargo-lambda);
    B --> C(Setup/Check Cache);
    C --> D{Cached?};
    D-->|No|E(Build)
    E-->F(Run Tests)
    D-->|Yes|F
    F-->Exit

sam-deploy

flowchart TD;
    A(Load Cache) --> B(Install AWS SAM CLI);
    B --> C(Set AWS Credentials);
    C --> D(Deploy);
    D-->Exit

Todo

Tool to generate env.* files based on prompts and automatically add to .gitignore
Enable/disable CORS in Lambda
Configurable log levels
Improve error handling
Add bucket creation to SAM template

Feedback

As I'm learning Rust (and AWS for that matter), I welcome constructive feedback that will help me improve. Please consider reaching out to me on any of the social networks listed on my profile page.

slashrawr/simple-rust-lambda