Explain the difference between `fs.readFile()` and `fs.createReadStream()` for reading files in Node.js.

0-2 years experience

1. 1We need to load a 5 KB JSON config file and send its contents in an HTTP response. Which fs API would you pick and why?
2. 2If you used fs.createReadStream to read a tiny text file, what would happen compared to using fs.readFile?

2-5 years experience

1. 1A new feature processes user‑uploaded CSV files. It works for files under 1 MB but crashes on larger ones. How would you debug the problem and decide between readFile and createReadStream?
2. 2During a code review you see a teammate using fs.readFile to pipe data into a network socket. What concerns would you raise and what alternative would you suggest?

5-8 years experience

1. 1Our video‑streaming service serves large files to many clients simultaneously. Explain how using fs.createReadStream versus fs.readFile impacts back‑pressure handling and memory usage under high concurrency.
2. 2Design the I/O layer for a log‑aggregation pipeline that reads huge log files, transforms each line, and writes to a remote store. How would you use streams to ensure scalability and fault tolerance?

8+ years experience

1. 1We are migrating a legacy batch job that reads multi‑gigabyte data dumps to a microservice architecture. Discuss the trade‑offs of keeping fs.readFile in some components versus moving everything to streaming, considering deployment, observability, and team ownership.
2. 2Multiple services in our organization have mixed usage of readFile and createReadStream for similar tasks, causing inconsistent performance. How would you create a company‑wide guideline and migration plan while balancing risk, testing, and backward compatibility?