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Leptos Starter Template for AWS Lambda

This is a template for the Leptos web framework managed with cargo-leptos and integrated with Axum for deployment on AWS Lambda.

Creating your template repo

If you don't have cargo-leptos installed you can install it with

cargo install cargo-leptos

Then either click the "Use this template" button in the Github UI or run

cargo generate --git https://github.com/leptos-rs/start-aws.git

to generate a new project template.

cd {{project-name}}

to go to your newly created project. Feel free to explore the project structure, but the best place to start with your application code is in src/app.rs. Additionally, Cargo.toml may need updating as new versions of the dependencies are released, especially if things are not working after a cargo update.

Running your project

cargo leptos watch

The --release flag enables the axum-aws-lambda layer, which only works within the AWS Lambda environment, so it should be avoided locally.

Installing Additional Tools

By default, cargo-leptos uses nightly Rust, cargo-generate, and sass. If you run into any trouble, you may need to install one or more of these tools.

  1. rustup toolchain install nightly --allow-downgrade - make sure you have Rust nightly
  2. rustup target add wasm32-unknown-unknown - add the ability to compile Rust to WebAssembly
  3. cargo install cargo-generate - install cargo-generate binary (should be installed automatically in future)
  4. npm install -g sass - install dart-sass (should be optional in future

Compiling for Release

cargo leptos build --release

Will generate your server binary in target/server/release and your site package in target/site

Testing Your Project

cargo leptos end-to-end
cargo leptos end-to-end --release

Cargo-leptos uses Playwright as the end-to-end test tool. Tests are located in end2end/tests directory.

Deploying Your Project

To build and deploy your project to AWS, you'll need cargo-lambda. They provide installation instructions on their site.

Let's start by building the project with cargo-leptos:

cargo leptos build --release

We won't use the server binary that it builds, since the Lambda function requires a particular architecture that cargo-lambda will handle for us. If you'd rather not build the server twice, you'll have to manage the WASM build and optimization yourself.

Next, let's build the production server binary:

LEPTOS_OUTPUT_NAME={{project-name}} cargo lambda build --no-default-features --features=ssr --release

This should produce a binary at target/lambda/{{project-name}}/bootstrap. Cargo.toml exposes all the required environment variables to cargo-lambda so that the server can run in production.

Finally, we can deploy the project to AWS:

cargo lambda deploy --include target/site --enable-function-url

After a few seconds, cargo-lambda should print out the URL of your deployed function!

This template provides a GitHub action that handles all these steps automatically. To use it, you'll need to provide your AWS credentials as repository secrets. You'll also need to provide the project name as a variable.

Notes

Credentials

You'll need AWS credentials with some permissions for IAM and Lambda operations. cargo-lambda provides the minimum requirements here.

Setting up permissions can be a bit onerous if this is your first time working with AWS. For a quick and dirty setup, you can:

  1. Create a new user in the IAM service (Access Management > Users)
  2. Click "Attach policies directly" on the "Set permissions" page
  3. Add the "AWSLambda_FullAccess" and "IAMFullAccess" policies, and complete the user creation
  4. Create an access key for the user, with "Use case" "Application running on an AWS compute service" (don't worry about the warning - just confirm)
  5. Save your credentials in an ~/.aws/credentials file (or the appropriate location for your system, for cargo-lambda deployments), or store the credentials in a password manager for later setting up CI/CD deploys; your AWS access key and secret key will look similar to the (randomly generated) example, below.
[default]
aws_access_key_id = AKIAQYLPMN5HCTNK35FD
aws_secret_access_key = rbWHpaI/lJnXdLteWHNnTVZpQztMB2+pdbb+KVgr

To use Github Actions to deploy to AWS Lambda, add the following variables and secrets to Github by going to your repo's "Settings" > "Secrets and Variables" > "Actions" and enter in the following:

Variables:

  • LEPTOS_OUTPUT_NAME - the name of your project, as in the Cargo.toml file
  • AWS_DEFAULT_REGION - the AWS region you want your Lambda deployed to, eg. us-west-2

Secrets:

  • AWS_ACCESS_KEY_ID - from AWS IAM credentials
  • AWS_SECRET_ACCESS_KEY - the secret key associated with the Access Key, from the AWS IAM step (above)

State

Since AWS Lambda is a serverless platform, you'll need to be more careful about how you manage long-lived state. Writing to disk or using an axum state extractor will not work reliably across requests. Instead, you'll need a database or other microservices that you can query from the Lambda function.

Optimizations

Serving static files from a lambda function is not the best approach. Ideally, you should upload your files to a CDN and configure your project to serve them from that location. AWS has an article on deploying React with SSR.

It's also pretty easy to set up edge compute with Lambda@Edge, which should improve latency for users around the world.