If you’re reading this, you likely own a Canary and you’re likely one of the many people on twitter requesting an API from Canary. For at least a year Canary has acknowledged those requests and redirected them to product. As consumers, we have yet to see an API or any concrete movements towards one.

The only interface Canary has that is close to an API are the calls their angular-based webapp makes when you login to the dashboard. The dashboard displays your devices, who is home, and a snapshot of the current sensor readings for each device.

That interface or “private API”, let’s say, has undergone a variety of changes over time, which I’ve written about here and here.

Between the writing of those two posts Canary made a change that seems to have disallowed querying past sensor data. The current “private API” only seems interested in pulling current sensor readings for your devices.

So what if you want this data for yourself? The most reasonable thing I’ve come up with is a private, secure polling and storage mechanism for your Canary device’s sensors (temp, humidity, air quality).

A few days ago I wrote about my first drop of the aws_canary_sensor_capture project which aims to achieve just that. This post is a more comprehensive walkthrough of what is all provided and what you need to set something similar up for yourself.

What does this thing do?

Generally speaking, the project leverages the serverless capabilities provided by Amazon Web Services (AWS) to securely poll, store, and govern access to your Canary device sensor data. The project uses Terraform to declare the AWS resources that compose the solution – with the addition of a bit of python code in the form of an AWS Lambda.

AWS Usage spans the following key areas:

  • KMS for encryption of your Canary account password and encrypted storage of the bearer token received from the Canary “private API”
  • API Gateway which provides the endpoint to access your sensor data, by device ID
  • Lambda for execution of the aforementioned python script
  • 2x DynamoDB tables; one for metadata and one for sensor data storage
  • Cloudwatch event rules for scheduled execution of the Lambda

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So what’s all happening under the hood and when?

  • The Cloudwatch event rules kick off the lambda. The lambda decrypts what it needs and checks to see if a metadata record exists in DynamoDB. If one does, it uses this data to poll each of the devices listed in the metadata record and stores those records in the another, sensor data DynamoDB table. If one does not, it will obtain a bearer token and the device IDs referenced in the account then proceed with fetching sensor data.
  • The API Gateway exists to allow a user (you) access to your data. The API Gateway supports read-only operations against your DynamoDB-hosted sensor data. There are no lambdas involved for these requests as request/response data flows through mapping templates only as it flows to and from the backend DynamoDB REST APIs.
  • KMS is used at the appropriate times to decrypt/encrypt your Canary account password and stored bearer token.

Obtaining and Usage

The project source code is hosted here and is easily leveraged in your own terraform project by declaring a module, specifying the source, and required input variables. For example:

module "canary" {
  source = "github.com/joshdurbin/aws_canary_sensor_capture"
  kms_arn = "arn:aws:kms:us-west-2:abc123abc123:key/aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee"
  canary_username = "bobsdinner@gmail.com"
  canary_encrytped_password = "..."
}

output "my_canary_sensor_capture_api_keys" {
  value = "${module.canary.api_keys}"
}

output "my_canary_sensor_capture_api_gateway_endpoint" {
  value = "${module.canary.api_gateway_endpoint}"
}

Note: There are additional, optional inputs to the aws_canary_sensor_capture module, which you can read about on the project readme.

The single, required resource dependency not provisioned for you within the aws_canary_sensor_capture module is the KMS key. You must create this key prior to usage of the module and leverage it to encrypt your Canary account password. The KMS ARN and encrypted account password are required variable definitions for the module. If you’re unsure how to do this, check the instructions listed in the module readme.

Accessing your sensor data

Terraform will create an API Gateway instance and API keys. The usage example above declares outputs that print the generated API keys and endpoint. These are optional! If you do not declare these outputs you will need to obtain them via the AWS API, Terraform state inspection, etc…

When you Terraform apply with the aws_canary_sensor_capture module in use you’ll get an output block declaring your endpoint and keys…

Outputs:

my_canary_api_gateway_endpoint = https://abc123defg.execute-api.us-west-2.amazonaws.com/production
my_canary_api_keys = [
    ABC123ABC123ABC123ABC123ABC123ABC123ABC1
]

There are two types of data to access:

  1. Canary device IDs
  2. Canary device sensor reading data

To access your device IDs, issue an HTTP GET request to the endpoint returned as an output from the aws_canary_sensor_capture module with the additional trailing /devices resource. Ex:

curl -H "x-api-key: ABC123ABC123ABC123ABC123ABC123ABC123ABC1" https://abc123defg.execute-api.us-west-2.amazonaws.com/production/devices

… which will return:

{
    "deviceIds": ["12345"]
}    

Finally, to access a devices data, issue an HTTP GET request to the same endpoint with the additional device ID resource. Ex:

curl -H "x-api-key: ABC123ABC123ABC123ABC123ABC123ABC123ABC1" https://abc123defg.execute-api.us-west-2.amazonaws.com/production/devices/12345

… which will return:

{
  "readings": [
    {
      "time": "2017-03-22T08:17:54.088573",
      "air_quality": "0.7394286281135604",
      "humidity": "73.37273965536741",
      "temperature": "18.44126831862636"
    },
    {
      "time": "2017-03-22T09:15:51.981384",
      "air_quality": "0.7774637438918911",
      "humidity": "73.23038767477068",
      "temperature": "18.25387227927232"
    }
  ]
}

Security

The AWS KMS key you define is central to the encryption/decryption and storage of your credentials to Canary. As the instructions state, you define this key and use it to encrypt your password, which you pass to the Terraform module. Terraform passes it, encrypted, as a parameter to the Python Lambda function.

The Lambda function uses the provided KMS key to decrypt your password and uses it with your username to fetch a bearer token whenever one isn’t already stored in the DynamoDB metadata table. The bearer token stored in DynamoDB is encrypted by the Lambda function when it’s stored for later use. This is done because the tokens Canary currently issues are relatively long-lived (at least a week).

The DynamoDB metadata table additionally stores your account’s device IDs, which are not encrypted. The sensor DynamoDB data storage table contains the deviceID and timestamp as a composite key with the sensor data for that device at that time. None of the sensor data is stored encrypted.

The API Gateway endpoints require auth tokens and are only accessible securely over the web.

Terraform Security Note

Terraform stores a wealth of data behind each resource that may or may not be visible to you (you can inspect by describing state resources). If you’re using remote storage with Terraform, you must enable server-side encryption.