This document contains a few essential instructions for developing new features and bug fixes for LocalStack.

t.b.a.

For the basic "CRUD" functionality of most services we're using a mock implementation (e.g., based on moto) in the background, and LocalStack adds a bunch of integrations on top of these services. We start up an HTTP proxy which intercepts all invocations and forwards requests to the backend. This allows us to add extended functionality without having to change the backend service.

The figure below illustrates the proxy mechanism and ports for the API Gateway service. (The default ports can be found in https://github.com/localstack/localstack/blob/master/localstack/constants.py )

 --------      -------------      -------------
| Client | -> |    Proxy    | -> |   Backend   |
|        |    | (port 4567) |    | (port 4566) |
 --------      -------------      -------------

The proxy follows a simple protocol by implementing 2 methods: forward_request which is called before a request is forwarded to the backend, and return_response which is called after a response has been received from the backend: https://github.com/localstack/localstack/blob/master/localstack/services/generic_proxy.py

The proxy implementation for API Gateway can be found here: https://github.com/localstack/localstack/blob/master/localstack/services/apigateway/apigateway_listener.py#L81

To enable a fast release cycle of LocalStack, we're using forked versions of various third-party libraries. For example, we have a forked version of moto which is published as a separate moto-ext pip package: https://github.com/whummer/moto/tree/localstack-fixes . If you decide to extend moto, you can either raise a PR against that repo, or against the main repo spulec/moto (then we need to take care of cross-merging and releasing new versions).