In this systems design mock interview, a Meta engineer asks the interviewee to design a live comments feature that displays new comments as they're posted without the need for refreshing or reloading the media content. This question is roughly on par with an M1 position however it should be noted that the degree of complexity for this question can range from L5 to L8 depending on the candidate and interviewer.

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🎨 High-level Design: https://strapi-iio.s3.us-west-2.amazo...

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TIMESTAMPS
00:00 - Introductions
02:45 - Question Starts
04:25 - Functional Requirements / Features
10:05 - Non-Functional Requirements
16:50 - API Design
17:32 - Latency Requirement and comment persistence
21:00 - Data Model and Capacity Estimates
24:07 - Interviewer Questions the API Design
27:28 - Interviewer believes this is the wrong way
29:00 - High-level Design
37:10 - Interviewer calls out single point of failure (message queue)
40:05 - Interviewer questions read API connection with subscription service
41:29 - Maintaining Manually vs Relying on HTTP protocol
43:07 - Long polling vs web socket and the difference between the first and second read
44:00 - What is the responsibility of the push service
45:54 - Feedback and results (hire/no hire)
47:55 - Level implications and trade-offs
51:35 - What went well and how to improve in interviews
54:05 - Example of non-functional requirements from the interviewer
1:00:04 - What is the core puzzle? (And extra tips)