Requirements of YouTube's Design

Scope the video service before estimating capacity. Distinguish source uploads, encoded renditions, playback transfers, and lightweight application requests; they have different resource costs.

Requirements

Designing a system like YouTube requires handling massive scale and reliability.

Functional requirements

We require that our system be able to perform the following functions:

1. Stream videos

2. Upload videos

3. Search videos by title

4. Like and dislike videos

5. Add comments

6. View thumbnails

Non-functional requirements

• High availability: Set separate targets for upload acceptance and playback. For perspective, 99% time-based availability permits 7.2 hours of downtime in a 30-day month; whether that is acceptable depends on the product.

• Scalability: Expand storage, processing, and delivery capacity as their measured workloads grow, while staying within agreed performance targets.

• Performance: Measure startup delay, rebuffering, and delivered quality. Low API latency alone does not imply smooth playback.

• Reliability: Uploaded content must not be lost or damaged.