sosw

sosw is a Python framework for bootstrapping AWS Lambda functions.

Built and maintained by SOSW LTD — we design AI-native serverless systems for production. Enterprise support & consulting →

Every Lambda gets the same production-grade skeleton in a dozen lines: the Processor base class with layered configuration (code defaults + DynamoDB/SSM overrides), automatic initialization of AWS clients, statistics counters, and a generated handler that caches the Processor across warm invocations. On top of that: LambdaApi — a declarative router for functions behind API Gateway, optional AWS durable execution support, and a battle-tested library of components and helpers. The only runtime dependency is boto3.

Quick example

from sosw.app import LambdaGlobals, get_lambda_handler, Processor as SoswProcessor


class Processor(SoswProcessor):

    DEFAULT_CONFIG = {
        'init_clients': ['sts'],    # Automatically initialize `self.sts_client`.
    }

    sts_client = None


    def __call__(self, event, **kwargs):
        super().__call__(event)
        return {'account': self.sts_client.get_caller_identity()['Account']}


global_vars = LambdaGlobals()
lambda_handler = get_lambda_handler(Processor, global_vars)

The Processor initializes once per Lambda container; warm invocations reuse it. Configuration can be overridden per function through the DynamoDB config table or SSM — no redeployment needed.

Installation

pip install sosw                # Python 3.12 - 3.14
pip install sosw[durable]       # + AWS durable execution support

Documentation

https://docs.sosw.app

• Quickstart — first Processor Lambda in minutes
• Concepts — Processor, warm start, configuration
• LambdaApi — HTTP APIs from a single Lambda
• Durable functions — long-running checkpointed workflows
• Migration guide — upgrading from the 0.7.x line

Coming from the 0.7.x line?

sosw began as the Serverless Orchestrator of Serverless Workers. The self-hosted orchestration layer (Orchestrator, Scheduler, Scavenger, Worker, and their managers) was removed in the 3.0 major release. Teams that use it should pin pip install 'sosw<3' (the 0.7.x line keeps working, and its docs are preserved at docs.sosw.app/previous/0.7.51) and plan the move to AWS Step Functions, EventBridge Scheduler, or durable functions — guidance in the migration guide.

Commercial support

sosw is open source (MIT) and built by SOSW LTD, the team that runs this pattern in production every day.

If your company is putting serverless Lambda systems into production and wants help — an architecture review, production hardening, a custom Lambda platform, or retained support — hire us.

We don't sell hype. We build systems that work.

Development

Getting started

Either pipenv:

pipenv sync --dev && pipenv shell

or plain pip in any virtual environment:

pip install boto3 pytest pytest-cov -r docs/requirements.txt

All package metadata lives in pyproject.toml (there is no setup.py).

Running tests

The unit suite is explicitly registered in sosw/test/suite_unit.py — new test files must be added there. It runs fully mocked (no AWS access) and is enforced at 100% line coverage in CI:

pytest ./sosw/test/suite_unit.py
pytest ./sosw/test/suite_unit.py --cov=sosw --cov-report=term-missing

Building the docs

pip install -r docs/requirements.txt
python -m sphinx -W -a -b html docs sosw-rtd; (cd sosw-rtd && python -m http.server)

Contribution guidelines

The full Contribution Guidelines with examples are in the documentation.

Release cycle

We follow both the Semantic Versioning pattern and PEP440 recommendations where they comply:

• Branches for planned staging versions follow the pattern X_Y_Z (Major_Minor_Micro), e.g. 3_0_1.
• Make your pull request against the closest staging branch (the smallest version after the latest release, of either the current or the next Minor).
• Pushes to staging branches automatically publish release candidates to TestPyPI.
• master merges are automatically packaged and published to PyPI.
• Keep your branch up to date with the branch you are making a PR to.

Example: if the latest released version on PyPI is 3.4.0, the open staging branches are 3_4_1 and 3_5_0. A bugfix PR targets 3_4_1; a new feature targets 3_5_0.

Code style

Follow PEP8, with the following specifications:

• both classes and functions are padded with 2 empty lines
• dictionaries are value-aligned

Copyright

This document has been placed in the public domain.

sosw - a framework for bootstrapping AWS Lambda functions

The MIT License (MIT)
Copyright (C) 2026  sosw core contributors <info@sosw.app>:
    Nikolay Grishchenko
    Sophie Fogel
    Gil Halperin

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