sigma-coding-challenge

A service in Node.js that exposes an API which can be consumed from any client. This service checks how many video streams a given user is watching and prevent a user from watching more than 3 video streams concurrently.

My Solution

I took a straightforward approach to this issue while keeping scalability in mind. I have decided to use AWS's serverless services (Lambda, API Gateway, and DynamoDB) to take adavantage of the automated scalability based on demand.

Installation and deployment instructions

Setting up the DB locally

To setup DynamoDD locally access the following link: Deploying DynamoDb Locally

Once the DynamoDB is setup locally, run the db on your computer (The command for this is different based on how you setup the local DB).

Create a new table by running the following script: aws dynamodb create-table --attribute-definitions AttributeName=userId,AttributeType=S --table-name user-streams-management-dev --key-schema AttributeName=userId,KeyType=HASH --billing-mode PAY_PER_REQUEST --output json --endpoint-url http://localhost:8000

Run the following command to verify that the table has been created: aws dynamodb list-tables --endpoint-url http://localhost:8000

Building the project locally

• Clone the project to your local machine
• Run npm install to install dependencies
• Run serverless offline to run the server locally
• Use an http client to test enpoints
  • I've provided a postman collection with all the endpoints in the collections directory of this repo

Endpoints

The solution has two http endpoints:

• Create user stream. This is used to create a new stream for the user based on the userId
  • Enpoint: http://localhost:3000/dev/streams/add
  • Method: POST
  • Sample Request body :

    {
        "userId": "ab-12345"
    }

• Remove user stream. This is used to remove a stream for the user based on the userId
  • Enpoint: http://localhost:3000/dev/streams/remove
  • Method: POST
  • Sample Request body :

    {
        "userId": "ab-12345"
    }

Deploying the project to AWS

In case the service needs to be deployed to AWS run the following command: serverless deploy --stage dev

To remove the project run the following command: serverless remove --stage dev

Scalability

Lambda

AWS Lambda provides a serverless compute service that can scale from a single request to hundreds of thousands per second. Lambda has two scaling quotas. Account consurrency quota and burst concurrency quota.

Account concurrency is the maximum concurrency in a particular Region. This is shared across all functions in an account. The default Regional concurrency quota starts at 1,000, which you can increase with a service ticket.

The burst concurrency quota provides an initial burst of traffic, between 500 and 3000 per minute, depending on the Region. This is also shared across all function in an account.

DynamoDB

For DynamoDB I've set the billing mode to pay_per_request. This allows us to use the database on-demand and only pay for the read and write requests that we use. This allows us to automatically scale with high traffic and scale down when traffic dies down.

API Gateway

API Gateway allows us to build services with no fixed costs and a pay-as-you-go pricing model. The service can handle any number of requests per second while making good use of system resources.