This is an ultra-slim, minimalistic custom runtime for AWS Lambda, with API bindings for C and Rust.

Features

• No abstraction bloat: HTTP Headers and JSON payload delivered in a raw char* buffer
• No dependencies outside of standard C library. Opt-in to whatever you actually need.
• Dynamically linked to glibc on target al2023 image, to minimize binary size
• No allocator dependency: Bring your own arena or gc allocator, or use malloc if you want
• (Optional) Rust language binding with no_std, no_main and no#tokio
• Rust binary is the same size as C binary (probably because of ELF page-boundary padding).

Benefits

• Extremely small deployment package size (~5kb zipped)!
• Extremely fast cold starts (4 to 5 milliseconds)
• Minimizes waste of compute resources, slowing down Global Warming!

Alternatives

Below is a comparison of AWS Lambda custom runtimes, focusing on cold start latency:

AWS Lambda Runtime	Cold Start	Link
This Project	under 5ms	https://github.com/refacktor-aws/aws-lambda-libc
Paul Almeida's C	n/a	https://github.com/PauloMigAlmeida/aws-lambda-c-runtime
Official Rust	40-80ms	https://github.com/awslabs/aws-lambda-rust-runtime
LLRT (JavaScript)	48-85ms	https://github.com/awslabs/llrt
Nim	10-40ms	https://github.com/refacktor-aws/nim-aws-sam
Zig	11ms	https://github.com/by-nir/aws-lambda-zig
Java/Graal AOTC	110ms	https://github.com/refacktor-aws/java-native-aws-lambda-without-frameworks
Plain JIT Java	400ms	n/a
All the rest	~200ms+	The python and nodejs runtimes are slower than they should be. Go is a little faster, C# is a little slower.

Project Structure

• src/: The C source code for the AWS Custom Runtime Interface implementation
• tests/: Unit-integration test using a mock server in Python to emulate the AWS Lambda Environment locally. Includes function.c, an example lambda function in C.
• sam-deploy/: Scripts for building & deploying using AWS SAM CLI in Docker. This is optional, you could alternatively use CDK, Terraform, the plain AWS CLI, etc.
• rust-binding/ & rust-example/: experimental Rust integration

Getting Started

Pre-requisites

• git clone (this project)
• docker container cli (e.g. Rancher Desktop, for building & local testing)
• aws configure (for deployment)
• python to run the build scripts

C

• python sam-deploy/deploy.py

Rust

• python rust-example/build-test-deploy.py