Stock Proxy

Overview

To design a system to interface with the third-party API in the given scenario, a stock proxy pattern will be used. This pattern allows to provide a substitute or placeholder for the external API, which can hide its shortcomings.

Functionality high-level overview

To address the limitations of the external API, a caching proxy service was implemented. This proxy service caches stock prices, preventing unnecessary repeated requests to the external API and mitigating the 1-second latency. Here's how the solution works:

• Cache: A cache is maintained to store recently fetched stock prices along with timestamps.

• Debouncing: To prevent concurrent requests from failing, we use a debouncing mechanism. If multiple requests for the same stock ticker come in concurrently, only the first one initiates a request to the external API. Subsequent requests wait for the ongoing request to complete and then receive the same result.

• Caching and Update: When a request is made, the cache is checked first. If the price is in the cache and not expired, it's returned. If it isn't, a request is initiated to the external API, updating the cache with the new price and timestamp, the StockPrice item.

Utilizing the solution

Install

Run yarn in this directory to install all dependencies.

Mock external API

For purposes of this challenge, the exampleServer.js will serve as a mock API. Start it running: yarn start:mock

Proxy server

Start the proxy server: yarn start:proxy

Next steps

To make this solution more robust and production-ready, consider the following next steps:

1. Monitoring and Logging: Implementing logging and monitoring to track the usage of the proxy and identifying any issues or performance bottlenecks.

2. Cache Eviction Strategy: Implementing a cache eviction strategy to ensure that the cache doesn't grow indefinitely, both Least Frequently Used and Least Recently Used would be eviction policies worth evaluating.

3. Error Handling: Enhancing error handling to handle different error scenarios from the external API.

4. Concurrency Control: Implementing concurrency control to manage a limited number of concurrent requests to the external API to prevent overwhelming it would be something else to take into consideration depending on the load and scalability requirements.

5. Security: If this service is exposed to the internet or used in a production environment, implementing security measures like rate limiting and authentication.

6. Testing: Writing unit tests and integration tests to ensure the reliability of the proxy service.