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A Node JS Local AWS S3 Static Web and API Gateway Server

This repo was developed so I could locally test an app that consists of:

  • A static web site served from S3
  • An associated REST API served by the API Gateway
  • A Node JS client that uses a websocket served by API Gateway V2

Notable Features

  • localAwsApiGw is an integrated Node JS server that runs locally and emulates the AWS interface for S3 static web and REST and WebSocket API Gateways.
  • Static web and lambda integration files are loaded from their local development location so are the same as what eventually gets deployed in the AWS cloud.
  • SAM/Cloudformation REST and WebSocket templates are read and parsed to create the routing information and environment variables used by the lambda integrations and are therefore also the same as what eventually gets deployed in the AWS cloud.
  • The developer can specify default AWS environment variables.
  • localAwsApiGw generates the appropriate lambda integration event and context arugments.
  • The environment variable LOCAL_AWS_GW is set to true so that lambda integrations can detect when running locally, if required (see example below).

Installation

git clone [email protected]:boblund/localAwsApiGw.git
cd localAwsApiGw
npm install

Use of HTTPS requires configuring the appropriate key and self-signed certificate in the directory where localAwsGw is running. The following openssl command can be used:

openssl req -x509 -newkey rsa:4096 -keyout <hostname>.key -out <hostname>.cert -sha256 -days <cert expirary> -nodes

Where is hostname where localAwsGw is running. For example

openssl req -x509 -newkey rsa:4096 -keyout pi.local.key -out pi.local.cert -sha256 -days 3650 -nodes

Creates pi.local.key and pi.local.cert files containing the key and certificate for pi.local that expire in 3650 days.

Use

Set up default lambda environment

A lambda's execution environment consists of: process.env and the event and context parameters. These are defined, in part, by the SAM/Cloudformation template. Other values may be required and can be added:

  • process.env: The lambda's process.env is set in the following order:
    • The lambda's template environment variables.
    • The contents of localGwEnv.js.
    • Local process environment variables that are present in either of the two above.
  • event and context: Modify event and context apiGw.invoke arguments in restApiGw.js or wsApiGw.js as required.

The files aws-rest-event-env.json and aws-ws-event-context.json show the AWS default values for process.env, event and context.

Modify Websocket lambda functions if necessary

Websocket lambda integrations need to be modified to detect when running locally to use local versions of AWS.ApiGatewayManagementApi.postToConnection().promise() and AWS.ApiGatewayManagementApi.getConnection().promise().

For example:

const postToConnection = context.clientContext
  ? (o) => { return context.clientContext.postToConnection(o)} //localApiGw
  : (o) => { return apigwApi.postToConnection(o).promise() } //AWS

then

// send message on a websocket
await postToConnection({
  ConnectionId: your.connectionId,
  Data: yourStringData
})

Running the server

SOME_VAR=xxx PORT=yyy node localAwsGw.js --web=dir | --rest=dir [restT=template.yaml] | --ws=dir [wsT=template.yaml]

SOME_VAR is a lambda environment variable to override

PORT is where the server will listen.

dir is the absolute or relative path to the server files:

  • --web static web pages
  • --api REST api files
  • --ws websocket api files

restT and wsT default to template.yaml but can be anything.[yaml|json|yml].

Example:

PORT=3000 node localAwsGw.js --web=webPageFiles --rest=restApiFiles --ws=wsApiFiles --wsT=myTemplate.json

Disclaimer

I use this for testing my project with two SAM templates for the REST API and Websocket API. I have no experience with how well apiGwLambdas.js will parse other templates to create the routes and environment so check the returned objects if things don't work.

Acknowledgements

Parts of the implementation are based on others' work with approriate links in the code.

License

Creative Commons Attribution-NonCommercial 4.0 International