Backend take-home exercise for Converge

The purpose of this exercise is to test your ability to build a basic data ingestion server in node.js.

The Converge Platform ingests sensor data from our customers' sites (these could be construction sites, factories, oil wells, etc.), does some processing (including alerting users for anomalous values) on them, and stores them, allowing them to be served from an HTTP API. This exercise will see you building a basic version of the infrastructure required to do this.

Part one: Data ingestion

The most basic requirement of the application is that it can ingest the data from sensors, storing them in some form of persistent storage such that these data can later be queried and retrieved. You will be expected to justify your choice of persistent storage.

Sensors will send data over HTTP, by making a request to PUT /data, with the following request body:

{
    sensorId: string,
    time:     int,
    value:    float,
}

This endpoint should exhibit the following behaviour:

Return error 400 if the packet does not contain sensorId;
Return error 400 if the packet does not contain time;
Return error 409 if the packet is a duplicate - (sensorId, time) pairings should be unique;
Return 204 if the packet structure is valid, and the packet was successfully stored in the persistent storage.

Part two: retrieving data

For these data to be useful, a client (e.g. a web app) must be able to query and retrieve them. You should create an endpoint which allows a client to retrieve data from a sensor. The endpoint should return suitable status codes, and the body of the request should be returned as JSON. An example of a suitable endpoint would be:

GET /data

With parameters:

sensorId: the sensor id for which to query data;
since: a lower bound on the time of the data;
until: an upper bound on the time of the data.

Part three: threshold alerts

Often, customers want to know if something is wrong, and therefore your application should have the ability to configure thresholds for individual sensors which can send a message (e.g. via email or SMS) when that threshold is tripped. For example, if the pressure on a fuel tank is too high it could explode, or if a pipe is too cold it could burst.

Requirements

The solution should be made available to us as a git repository (whether hosted or merely in an archive is up to you). It should be installable and runnable using the basic npm commands npm install and npm start.

Included files