Cloudformation Template - Amazon Lex Voice Setting Engine

Hi, Know you asked this 3mo ago and likely moved on, but answering in case others have the same question.

You're correct that the CFT support for Lex does not currently do anything with the 'Engine' property passed as part of the 'VoiceSettings'' property in a AWS::Lex::Bot resource. Behind the scenes, the AWS::Lex::Bot resource will result in an API call to create_bot_locale:

response = client.create_bot_locale(
    botId='string',
    botVersion='string',
    localeId='string',
    description='string',
    nluIntentConfidenceThreshold=123.0,
    voiceSettings={
        'voiceId': 'string',
        'engine': 'standard'|'neural'
    }
)

Because the 'engine' property is not honored, the value defaults to 'standard' in the API call.

I submitted a feature request but in the meantime, you can create a lambda custom resource or a CloudFormation resource type to overcome this. Your custom resource type would take in the same parameters currently passed in AWS::Lex::Bot and make a call to create_bot_locale API including the voiceSettings.engine property value which you would set to 'neural' in your template. Creating the Lambda custom resource is pretty trivial but you would need to support the update and delete cases as well. See docs for Lambda-backed Custom Resources, or the newer preferred mechanism, CloudFormation Registry Resource Types.