DNS Verify

A function to check DNS resolution and verify the correct setup of CNAMEs.

You can provide an FQDN and a list of acceptable CNAMEs, the function will return with a list of CNAMEs which the FQDN resolves to and a boolean if any of those are in the acceptable CNAMEs list.

Installation

Dependancies

Requires serverless framework and the [serverless-python-requirements plugin] (https://www.npmjs.com/package/serverless-python-requirements)

It also uses docker when deploying from a non-linux machine, to install the pip requirements in a linux environment.

Deployment

Then, the function can be deployed using sls deploy --stage production and it will deploy to 'eu-west-1' by default, use the --region REGION_ID flag to deploy elsewhere.

Usage

Once deployed sls will report back with an API KEY and an HTTPS endpoint. We will need to use these to make requests of the new service:

curl -X POST \
  https://$API-ENDPOINT/production/validate-cname \
  -H 'Content-Type: application/json' \
  -H 'x-api-key: $API_KEY' \
  -d '{
    "fqdn": "www.example.com",
    "valid-domains": "[example.com., non-valid.com.]"
}'

Example result

The result will come back as JSON:

{
    "success": {
        "valid": true,
        "cnames": [
            "example.com."
        ]
    }
}