timmy-timer

A lightweight app for scheduling timers with a callback

Local installation

• Clone the repository
• Run npm install in the project's root directory.
• You need to install the mysql and redis (on macos, recommended to use brew)
• Run npm run serve to start the server using nodemon.

Deployment with Docker

The full app with dependecies can be deployed using Docker and Docker Compose:

• Download docker (https://www.docker.com/products/docker-desktop)
• Clone the repository.
• Run docker-compose up -d - this will do the following:
  • Build the app and create an image.
  • Spawn three containers - app (nodejs), mysql and redis.
• The app will be available on localhost:3000 (default port; can be changed in the .env file).

APIs

POST /timers

Provide the time (hours, minutes, seconds) for the webhook and url. Request body:

{
  "hours": int,
  "minutes": int,
  "seconds": int, 
  "url": string
}

The response is the id of the created timer:

{ "id": int }

GET /timers/:id

Returns the remaining seconds of the given timer id:

{
  "id": int,
  "time_left": int
}

Stack

• NodeJS - backend runtime env
• ExpressJS - web application framework
• MySQL - persisting timers.
• Redis - queue management

DB Persisting and Queue Management

• The app is using MySQL as the persistence layer. All created timers will be saved to the timmy.timer table.
• Queue management is done using redis:
  • Using a ZSET (sorted set) to add newly created timers, sorted by the future execution time.
  • A worker is querying the queue every x milliseconds (defined by the QUEUE_PROCESS_EVERY_MS env variable).
  • If there are jobs to be executed, they will be removed from the queue and processed.