AWS Lambda Runtime Interface Client for Python

Warnings

• breaking Version 3.0.0 of `awslambdaric` dropped support for Python runtimes older than 3.9. Functions using Python versions 3.8 or earlier will no longer work with `awslambdaric` v3.0.0 and newer.
  Fix: Upgrade your Python runtime to 3.9 or newer (e.g., Python 3.13 support was added in v3.0.0) and ensure your `awslambdaric` dependency is compatible.
• deprecated AWS Lambda will deprecate Python 3.9 runtime. New functions using Python 3.9 will be blocked from creation after January 15, 2026, and existing functions cannot be updated with Python 3.9 after February 15, 2026.
  Fix: Plan to upgrade your Lambda functions to Python 3.10 or later versions. While `awslambdaric` itself supports Python 3.9+, the underlying Lambda service is deprecating the 3.9 runtime.
• gotcha When upgrading Python runtime versions for Lambda functions (e.g., from 3.7 to 3.9), ensure that external dependencies are correctly packaged at the root level of your deployment, not within a 'packages' folder, as the underlying Python runtime search path changed.
  Fix: Adjust your packaging script or `Dockerfile` to install dependencies directly into the root of your function's deployment directory (e.g., `/var/task`) or ensure they are properly accessible on the `PYTHONPATH`.
• gotcha Incorrect configuration of `ENTRYPOINT` and `CMD` in Dockerfiles for custom runtimes is a common error. The `awslambdaric` module must be the `ENTRYPOINT`, and your function's handler path the `CMD`.
  Fix: Ensure your Dockerfile correctly sets `ENTRYPOINT ["/usr/local/bin/python", "-m", "awslambdaric"]` and `CMD ["your_module.your_handler_function"]`.
• gotcha Historical compatibility issues with the `simplejson` dependency (e.g., lack of Python 3.9 wheels for older `simplejson` versions) could lead to installation failures.
  Fix: `awslambdaric` versions 2.0.11 and newer (including 3.x and 4.x) have updated `simplejson` dependencies to be compatible with newer Python versions. Ensure you are using a recent `awslambdaric` version.
• gotcha Version 3.0.0 introduced support for SnapStart runtime hooks. If you are leveraging AWS Lambda SnapStart, be aware of the new hooks and how they might affect your function's initialization lifecycle.
  Fix: Review the AWS Lambda documentation on SnapStart runtime hooks for Python to understand how to implement `after_restore` and `before_checkpoint` if your function uses SnapStart.

Install

• pip install awslambdaric Install latest version

Imports

• LambdaRuntimeException

  from awslambdaric.lambda_runtime_exception import LambdaRuntimeException

  While awslambdaric itself is typically invoked by the Lambda runtime (e.g., via Dockerfile ENTRYPOINT), specific components like exception classes can be imported for custom runtime implementations or advanced error handling.

Quickstart

This quickstart demonstrates how to create a Python Lambda function using a custom container image with `awslambdaric`. You define your Lambda handler in `app.py` and then create a `Dockerfile` that installs `awslambdaric` and sets it as the container's entrypoint, with your function handler as the command. This allows the Lambda service to properly invoke your Python code within the custom runtime environment.

# app.py
def handler(event, context):
    print(f"Received event: {event}")
    print(f"Context: {context.aws_request_id}")
    return {"statusCode": 200, "body": "Hello from Lambda!"}

# Dockerfile
FROM python:3.9-slim-buster

# Set working directory
WORKDIR /var/task

# Copy function code
COPY app.py .

# Install awslambdaric and any other dependencies
RUN pip install --no-cache-dir awslambdaric

# Set the ENTRYPOINT to the AWS Lambda Runtime Interface Client
ENTRYPOINT ["/usr/local/bin/python", "-m", "awslambdaric"]

# Set the CMD to your Lambda handler
CMD ["app.handler"]