Custom runtimes are a powerful feature provided by AWS Lambda and other serverless platforms, enabling developers to run languages that aren't officially supported out of the box. This flexibility allows you to use your language of choice— even Elixir— in Lambda environments.
A custom runtime lets you package your language runtime, dependencies, and logic into a deployable layer. When Lambda is triggered, it starts with your provided runtime, passing events and returning results through standard input and output, following a prescribed interface. This lets you fully control your environment and use any programming language.
How Custom Runtimes Work
- Runtime Layer: You bundle the language runtime (such as Elixir and Erlang's BEAM VM) with any supporting libraries into a layer that's loaded by Lambda at invocation.
- Handler Function: The entry point for your code is the handler, which processes incoming Lambda events.
- Invocation and Bootstrapping: On each event, Lambda starts your environment, invokes your handler, and expects your runtime to handle communication using streams.
- Cold Starts: Custom runtimes may face higher cold start times since both your code and runtime must be initialized, possibly increasing overhead.
- Interface Contract: Your runtime must strictly adhere to AWS Lambda’s interface for proper initialization, processing, and cleanup of events.
Why Use an Elixir-Specific Runtime?
Rather than building a generic runtime, purpose-built projects like Mayfly - Elixir AWS Lambda Runtime streamline Lambda adoption for Elixir developers:
- Pure Elixir Functions: Write regular Elixir modules and functions; no wrappers or awkward conventions are required.
- Familiar Patterns: Use the same libraries, tooling, and stack traces as in any Elixir project, improving maintainability and developer productivity.
- Minimal Setup: Get started by simply adding Mayfly as a dependency:
elixirdef deps do {:mayfly, github: "bmalum/mayfly"}end
- Easy Build and Deploy: Build a Lambda-compatible ZIP with
mix lambda.build --zip --docker, upload, and set your handler toElixir.MyFunction.handle. Mayfly supports ARM64—for best results, choose "arm64" in the AWS Console if building on Apple silicon or ARM processors.
Practical Example
Here’s what a minimal Elixir Lambda handler looks like:
elixirdefmodule MyFunction do def handle(event) do {:ok, %{message: "Hello from Elixir!", event: event}} endend
Deploying your code is straightforward, allowing you to focus on business logic rather than Lambda integration details.
Trade-Offs and Considerations
- Complexity: You need to maintain the runtime environment, ensure dependencies are up to date, and test for compatibility.
- Performance: Cold starts may be longer than with official runtimes, and VM-centric languages like Elixir can have additional overhead.
- Support: Official runtimes benefit from deeper AWS support and a wider community, but community-driven runtimes like Mayfly are gaining traction and offer clear benefits for Elixir-specific workflows.
Learn More and Try It
If you want to run Elixir on AWS Lambda with minimal fuss, full power, and the expressiveness the language offers, check out elixir-aws-lambda.dev for guides, examples, and details on the Mayfly runtime. This project directly addresses the needs of Elixir developers targeting serverless deployments and is optimized for both reliability and the language’s unique strengths.