Voice-enabling smart-home devices with Amazon Alexa (Part III)

In the previous installment of our Alexa skills development exploration, we got to the point of building smarthome and custom skills for Amazon Echo. We used tools babel and webpack to transpile modern ES6/ES7 JavaScript into an older JavaScript version supported by Amazon Lambda. Now, our project produces a single output with either the smart-home or the custom Alexa skill. We are able to manually compress the transpiled JavaScript and upload it to Amazon Web Services using the Lambda console.
We, however, want the deployment done automatically. We will configure serverless framework files to:
– compress our Lambda code,
– create a new “stack” on the AWS side, if necessary,
– copy the Lambda to Amazon and set its’ invocation trigger.

Our main serverless configuration file is serverless.yml. It has definitions split between function-level configurations and ones relevant to the specific stage and locality. It looks like:

service: ${file(./${env:DEPLOY_FILE_NAME}):service}

provider:
 name: aws
 custom:
   globalSchedule: ${file(./${env:DEPLOY_FILE_NAME_STAGE}):globalSchedule}
   roleName: ${file(./${env:DEPLOY_FILE_NAME_STAGE}):roleName}
   profileName: ${file(./${env:DEPLOY_FILE_NAME_STAGE}):profileName}
 plugins:
   - pluginHandler
   - serverless-alexa-plugin
 runtime: nodejs4.3
 cfLogs: true
 stage: ${file(./${env:DEPLOY_FILE_NAME_STAGE}):stage}
 region: ${file(./${env:DEPLOY_FILE_NAME_STAGE}):region}
 memorySize: ${file(./${env:DEPLOY_FILE_NAME_STAGE}):memorySize}
 timeout: ${file(./${env:DEPLOY_FILE_NAME_STAGE}):timeout}
 keepWarm: false
 useApigateway: false

package:
 exclude:
   ${file(./${env:DEPLOY_FILE_NAME}):exclude}
functions:
 lambdaHandler:
   handler: ${file(./${env:DEPLOY_FILE_NAME_STAGE}):handler}
   events:
     ${file(./${env:DEPLOY_FILE_NAME}):events}

When settings apply to the function regardless of the deployment stage, we keep them in DEPLOY_FILE_NAME.
For example, our custom skill configuration looks like the below:
service: alexa-CustomSkillAdapter
exclude:
 - src/**
 - test/**
 - webpack/**
 - dist/**
 - build/**
 - node_modules/**
 - UiTest/**
 - bower.json
 - CHANGELOG.md
 - deploy.sh
 - jsconfig.json
 - karma.conf.js
 - LICENSE
 - package.json
 - pluginHandler.js
 - README.md
 - serverless_settings/**
 - settings_eu_customskill.yml
 - settings_eu_smarthome.yml
 - settings_us_customskill.yml
 - settings_us_smarthome.yml
 - .idea/**
 - .npmignore/**
 - .jshintrc
 - event.json
 - lambda_function_smart_home.js
 - documentation.docx
events:
 - alexaSkill

The serverless framework documentation covers what parameters are supported. We just want to draw your attention to the events setting. Our lambda functions do not use storage or databases, and only require events that trigger the Alexa intents processing. For custom skill, this event type is alexaSkill. At the time this article is being written, serverless does not support Alexa Smart Home events, so the smarthome skill trigger needs to be set manually. The AWS CloudFormation lack of support for Smart-Home events as AWS Lambda triggers is due to a unimplemented feature, already on AWS roadmap – EventSourceToken property for the AWS::Lambda::Permission. However, if you want to automatically set the trigger now, before the feature is implemented by Amazon Web Services, it is still possible using a simple shell script. Using the aws command line tools, you could set the trigger by executing the below command:

$ aws lambda add-permission --function-name $MY_FUNCTION_NAME --action lambda:InvokeFunction --principal $PRINCIPAL --region $AWS_REGION --event-source-token $ALEXA_SKILL_ID --statement-id 8

We have now covered the design and implementation of an Alexa skills project, for connected devices. Using babel, webpack and serverless, we were able to create a single Node.JS project used to produce and automatically deploy both custom and smart-home Amazon Alexa skills. The builds script allow specifying different configurations depending on stage and locality.
If you have questions or need assistance with your Amazon Alexa projects, please contact us and maybe we could help. If you are interested in controlling smart-home devices with your voice, stay tuned. We are about to publish a post on building Google Assistant Home Control Actions.

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