Writing an Alexa skill using Ruby and AWS Lambda

2020-12-03

What we’re doing

This post gets us started with AWS SAM and creates a demo hello world lambda function using Ruby.

Prerequisites

Follow the instructions listed in AWS SAM explaining how to

• Create an AWS account:
• Configure IAM permissions.
• Install Docker. Note: Docker is only a prerequisite for testing your application locally.
• Install Homebrew.
• Install the AWS SAM CLI.

At the end of this step, you should be able to successfully run sam --version at the command line and get back something like ‘SAM CLI, version 1.13.2’.

Creating a Hello world app

Follow the instructions in the tutorial to deploy a ‘hello world’ app to AWS (don’t forget to select Ruby), or follow here:

Start by

sam init

Enter the highlighted data as you’re prompted, selecting your own name for the app, of course:

At the end of this process, something like this would have been displayed:

Now run (substituting your app’s name):

cd lambda-alexa-myinfo
bundle

At this stage, the app is ready to be run locally, tested, or to be deployed.

Running locally

sam local start-api will start a local instance at ‘localhost:3000’, and you can reach it by curl localhost:3000/hello-world, you will get a 403 authentication error.

The better way to test this is to issue sam local invoke that will create an image and run its container locally for testing:

Running tests

sam init also created a test in tests/unit. To run them using Rake, create a Rakefile at the root of the project and paste the following into it:

require 'rake/testtask'

task default: "test"
Rake::TestTask.new do |task|
  task.pattern = 'tests/**/test_*.rb'
end

Save the file and issue rake at the command line.

If the test fails, I think it’s because HTTParty is called with a failing expectation. I did not see the value in this and faked out the mock call to HTTParty. Comments welcome!

def test_lambda_handler
  HTTParty.expects(:get).with('http://checkip.amazonaws.com/').returns(mock_response)
  response = HTTParty.get('http://checkip.amazonaws.com/')
  response.body
  response.code
  assert_equal(lambda_handler(event: event, context: ''), expected_result)
end

Deploying the app

Issue sam build, and answer the questions as per your environment. Note that I am skipping the auth question:

Using the URL given to us at the end of the output, we can curl for the response:

curl https://<your path here>.execute-api.us-east-1.amazonaws.com/Prod/hello/

and visit that address using a browser.

What happened with my AWS account?

Once deployed, these will be the visible changes to your account:

• A new S3 bucket was created to hold the source code and template.
• A lambda function was created and registered.
• An API Gateway was created to route requests to the function.
• CloudFormation stacks

What’s next?

Wire up functions to handle Alexa requests