Good Lambda Have Function

Code Lambda for fun and profit.

Description

This library trivializes creating powerful AWS Lambda handler functions with minimal boilerplate.

This creates a handler that invokes another AWS Lambda function:

import { asClass } from 'awilix'
import { LambdaClient } from '@pureskillgg/awsjs'
import { ssmString } from '@pureskillgg/ace'
import { invokeHandler } from '@pureskillgg/glhf'

const parameters = {
  blueLambdaFunction: ssmString('BLUE_LAMBDA_FUNCTION_SSM_PATH')
}

const createProcessor = ({ blueLambdaClient, log }) => async (
  event,
  container
) => {
  return blueLambdaClient.invokeJson(event)
}

const registerDependencies = (container, config) => {
  container.register(
    'blueLambdaClient',
    asClass(LambdaClient).inject(() => ({
      name: 'blue',
      functionName: config.blueLambdaFunction,
      AwsLambdaClient: undefined,
      params: undefined
    }))
  )
}

export const createHandler = invokeHandler({
  parameters,
  createProcessor,
  registerDependencies
})

export const handler = createHandler(parameters)

Installation

Add this as a dependency to your project using npm with

$ npm install @pureskillgg/glhf

or using Yarn with

$ yarn add @pureskillgg/glhf

Usage

A trivial handler that does nothing may be created like this

import { invokeHandler } from '@pureskillgg/glhf'

const createHandler = invokeHandler()
export const handler = createHandler()

To create a more useful handler, leverage parameters, createProcessor, and registerDependencies,

import { invokeHandler } from '@pureskillgg/glhf'

const createHandler = invokeHandler({ createProcessor, registerDependencies })
export const handler = createHandler(parameters)

• Use parameters to load configuration with AWS Config Executor.
• Use registerDependencies to register things with side-effects that should be mocked out in tests. This function has access to the configuration loaded via parameters.
• Use createProcessor to define the business logic for handling each event. This function is registered with the Awilix container as a factory function, thus it can access all dependencies registered using registerDependencies.

Handler Factories

All exported handler functions return a new handler factory with identical signature:

1. parameters: The AWS Config Executor parameters to load.
2. t: The AVA t object (if running inside AVA).
3. overrideDependencies: A function with signature (container, config) => void which will be called immediately after registerDependencies.

These arguments are all designed to facilitate testing. See handlers and test/handlers.

The async function returned by the factory has a signature (event, context) => any matching the signature expected by AWS Lambda.

All handlers execute these steps in order:

1. Load the config defined by the parameters.
2. Create a new Awilix container and register the default dependencies: log, reqId, and processor.
3. Parse the event with the parser.
4. Execute the processor on the event using the configured strategy and wrapper.
5. Serialize and return the result.

Invoke Handler

The invokeHandler handles AWS Lambda invocation events.

An invocation event is a plain JSON serializable JavaScript object. This handler may thus be used to handle any invocation event if a more specific handler is not provided.

Example

import { invokeHandler } from '@pureskillgg/glhf'

const createProcessor = () => async (event, ctx) => {
  return { hello: 'world' }
}

const createHandler = invokeHandler({ createProcessor })

export const handler = createHandler()

EventBridge Handler

The eventbridgeHandler handles EventBridge events.

Dead-letter queue redrive

Additionally, this handler supports redriving events from dead-letter queues connected to both onFailure and event rules.

The full lifecycle of an event is explained below:

• EventBridge invokes the function as an Asynchronous invocation.
• If EventBridge cannot invoke the target function, it will put the event in the DLQ after exhausting the allotted retry attempts.
• If EventBridge can invoke the function it will consider the event delivered, even if the function invocation throws an error.
• If the asynchronous function invocation throws an error, it will put the invocation record in the DLQ after exhausting the allotted retry attempts.
• If the DLQ message is from EventBridge, the message body is the event record.
• If the DLQ message is from Lambda, the message body contains the event record inside the requestPayload attribute.

The example below shows how to configure a Serverless function that will deliver failed messages to a DLQ and allow redriving failed messages with the same function.

Example

import { eventbridgeHandler } from '@pureskillgg/glhf'

const createProcessor = () => async (event, ctx) => {
  return { type: event['detail-type'] }
}

const createHandler = invokeHandler({ createProcessor })

export const handler = createHandler()

event:
  handler: handlers/event.handler
  destinations:
    onFailure: ${ssm:${self:custom.ssmPrefix}/event_deadletter_queue_arn}
  events:
    - eventBridge:
        eventBus: ${ssm:${self:custom.ssmPrefix}/eventbus_arn}
        deadLetterQueueArn: {ssm:${self:custom.ssmPrefix}/event_deadletter_queue_arn}
    - sqs:
        enabled: false
        arn: ${ssm:${self:custom.ssmPrefix}/event_deadletter_queue_arn}
        batchSize: 1

SQS Handler

The sqsHandler handler handles SQS events.

Since SQS events contain multiple messages, the default strategy for this handler will execute the processor on each message in parallel. Each message will be processed in a child Awilix scope.

The sqsJsonHandler behaves like the sqsHandler except it will parse the SQS message body as JSON.

HTTP Handler

The httpHandler handler handles API Gateway Proxy events.

The handler will catch all processor errors, wrap them with Boom, and return a basic status code response. If the processor throws a Boom error, its status code will be respected.

The httpJsonHandler behaves like the httpHandler except it will parse the request body as JSON, and if the processor returns an object with a body property, it will serialize that to JSON and add any missing response properties.

Example

import { sqsJsonHandler } from '@pureskillgg/glhf'

const createProcessor = () => async (event, ctx) => {
  return event.body
}

const createHandler = sqsJsonHandler({ createProcessor })

export const handler = createHandler()

Advanced usage

The handler functions take additional options: logOptions, parser, serializer, createWrapper, and createStrategy. These are advanced features which are stable, but not yet fully documented. They are used internally to create the included handler factories. Please refer to the code for how they may be used.

Parsers and serializers

A parser is a synchronous function which transforms the raw AWS Lambda event before it is passed to the processor.

A serializer is a synchronous function which transforms the output of the processor into the final return value of the AWS Lambda function.

Parsers and serializers should be agnostic to details of user input and response content. They are not expected to throw runtime errors. If a parser or serializer throws, it indicates a bug in its implementation, or a bad configuration (e.g., trying to parse payloads for the wrong event type).

Wrappers

A wrapper function must call a strategy with the event and context. It may optionally call the logger, parser, and serializer.

Strategy

A strategy has access to the Awilix container scoped to the event. It should resolve and call the processor and optionally handle errors.

Development and Testing

Quickstart

$ git clone https://github.com/pureskillgg/glhf.git
$ cd glhf
$ nvm install
$ yarn install

Run the command below in a separate terminal window:

$ yarn run test:watch

Primary development tasks are defined under scripts in package.json and available via yarn run. View them with

$ yarn run

Source code

The source code is hosted on GitHub. Clone the project with

$ git clone [email protected]:pureskillgg/glhf.git

Requirements

You will need Node.js with npm, Yarn, and a Node.js debugging client.

Be sure that all commands run under the correct Node version, e.g., if using nvm, install the correct version with

$ nvm install

Set the active version for each shell session with

$ nvm use

Install the development dependencies with

$ yarn install

Publishing

Use the npm version command to release a new version. This will push a new git tag which will trigger a GitHub action.

Publishing may be triggered using on the web using a version workflow_dispatch on GitHub Actions.

Deployment

Serverless deployment is triggered by a release repository_dispatch on GitHub Actions.

Deployment may be triggered using on the web using a release workflow_dispatch on GitHub Actions.

GitHub Actions

GitHub Actions should already be configured: this section is for reference only.

The following repository secrets must be set on GitHub Actions:

• NPM_TOKEN: npm token for publishing packages.
• AWS_DEFAULT_REGION: The AWS region Serverless will deploy to.
• AWS_ACCESS_KEY_ID: AWS access key ID.
• AWS_SECRET_ACCESS_KEY: AWS secret access key.
• GH_TOKEN: A personal access token that can trigger workflows.
• GRAFANA_API_ORIGIN: The Grafana origin to push annotations.
• GRAFANA_API_KEY: The Grafana key key for pushing annotations.
• DISCORD_WEBHOOK: The Discord webhook to notify on deploy.
• SENTRY_AUTH_TOKEN: The Sentry auth token.

These must be set manually.

Secrets for Optional GitHub Actions

The version and format GitHub actions require a user with write access to the repository. including access to trigger workflows and read and write packages.

Set these additional secrets to enable the action:

• GH_USER: The GitHub user's username.
• GH_TOKEN: A personal access token for the user.
• GIT_USER_NAME: The GitHub user's real name.
• GIT_USER_EMAIL: The GitHub user's email.
• GPG_PRIVATE_KEY: The GitHub user's GPG private key.
• GPG_PASSPHRASE: The GitHub user's GPG passphrase.

Contributing

Please submit and comment on bug reports and feature requests.

To submit a patch:

1. Fork it (https://github.com/pureskillgg/glhf/fork).
2. Create your feature branch (git checkout -b my-new-feature).
3. Make changes.
4. Commit your changes (git commit -am 'Add some feature').
5. Push to the branch (git push origin my-new-feature).
6. Create a new Pull Request.

License

This npm package is licensed under the MIT license.

Portions of code in this project were taken and adapted from @meltwater/jackalambda which is licensed under the MIT license.

Warranty

This software is provided by the copyright holders and contributors "as is" and any express or implied warranties, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose are disclaimed. In no event shall the copyright holder or contributors be liable for any direct, indirect, incidental, special, exemplary, or consequential damages (including, but not limited to, procurement of substitute goods or services; loss of use, data, or profits; or business interruption) however caused and on any theory of liability, whether in contract, strict liability, or tort (including negligence or otherwise) arising in any way out of the use of this software, even if advised of the possibility of such damage.