Weather Forecast Service

Overview

This service provides real-time weather information by integrating with the OpenWeatherMap API. It is designed for efficiency and scalability, utilizing a caching strategy to enhance response times and minimize external API requests.

Code Walkthrough

Service Architecture

Key components of the architecture include:

• Swappable API Sources: The architecture is designed for flexibility, allowing for the integration of additional weather data sources via the IWeatherService interface.
• Swappable Caching Mechanisms: Features an in-memory cache for development (InMemoryCache) and a Redis cache for production (RedisCache), through the ICache interface.
• WeatherService: Orchestrates the retrieval of weather data, preferring cached data when available. It implements composition by combining caching (ICache) and weather data fetching (OpenWeatherMapService) for effective data management.
• The application uses Controllers and Routes within Express to manage HTTP requests.

Docker-Based Setup

This setup uses Docker to containerize the application and its dependencies, including Redis for caching.

Local Setup Using Docker

Prerequisites

• Docker and Docker Compose installed on your machine.
• An API key from OpenWeatherMap.

Configuration

1. Clone the repository and navigate to the project directory.
2. Create a .env file in the root directory based on the provided .env.example. Fill in the necessary environment variables, including your OpenWeatherMap API key and preferred port for the application. The Redis configuration will be handled by Docker Compose. Note that setting an ENV=PROD will use Redis as a caching mechanism, whereas all other value for this setting will use an in-memory caching mechanism.

Running with Docker Compose

To run the application, execute the following command in the terminal at the root of the project directory:

docker-compose up --build

This command builds the Docker image for the application and starts the containers defined in docker-compose.yml, including the Redis service. The application will be accessible on the port specified in your .env file at http://localhost:<port>/weather/<city>.

Getting Weather Data

To retrieve weather data for a specific city, use the following curl command. Replace YourCityName with the name of the city you're interested in:

curl -X GET "http://localhost:3000/weather/YourCityName"

This command sends a GET request to the server, which responds with the weather data for the specified city. If the city's weather data is cached and not yet expired, the server will return the cached data. Otherwise, it will fetch new data from the OpenWeatherMap API, cache it, and then return it.

Forcing a Recache of Weather Data

If you want to force the server to fetch fresh weather data from the OpenWeatherMap API regardless of whether it's already cached, add a forceUpdate query parameter set to true:

curl -X GET "http://localhost:3000/weather/YourCityName?forceUpdate=true"

By including ?forceUpdate=true in the request URL, you instruct the server to bypass any existing cache for the specified city and retrieve new data from the OpenWeatherMap API, which in turn gets cached.

Verifying Data Source

For the sake of this assignment, the source of the data (whether fetched from API or from cache) is logged to the console.

Testing

The project includes a suite of automated tests using Jest. To run these tests, you do not need to have the application running via Docker. Instead, follow these steps:

Ensure all dependencies are installed by running npm install if you haven't already. Execute the test suite with:

npm run test

Assumptions and Technical Choices

• Redis: Selected for production-level caching for its speed and reliability.
• Singleton Patterns: Used for caching instances to optimize resource use.
• Composition: Facilitates flexibility in managing weather data retrieval and caching.

Future Optimizations and Scale

Scalability

• The use of composition in the service architecture inherently supports scalability. By structuring the WeatherService to interact with implementations of ICache, more sophisticated caching strategies can be implemented without major overhauls to our service's core logic. Likewise, new weather APIs can be swapped out with implementations of IWeatherService.

Optimizations

A few thoughts on optimizations:

• Integrate a circuit breaker for the OpenWeatherMap API calls to prevent failures in case of API downtime or rate limiting.
• Better error handling, custom error classes

Features

• Extend the service to support additional endpoints from OpenWeatherMap, such as forecast data.
• Add user authentication to enable personalized weather dashboards.