This is the kind of question where you can talk for five minutes and still feel like you only scratched it.
Start by clarifying the core difference: WebSockets provide full-duplex communication, while SSE is unidirectional (server-to-client). Then, walk through the trade-offs in directionality, reconnect behavior, and back-pressure, and conclude with scenarios where each is preferable, tying back to Snapchat's real-time needs.
Pro tip: Mention that SSE is often underrated for server-to-client streaming because it works over HTTP/2, has built-in reconnection, and is simpler to scale—showing you consider operational simplicity, not just technical capability.
Determine if the application requires bidirectional communication (e.g., chat, gaming) or only server-to-client updates (e.g., live feeds, notifications).
Explain that SSE has automatic reconnection with Last-Event-ID, while WebSockets require manual reconnection logic and state recovery.
Discuss how WebSockets allow application-level flow control (e.g., pausing reads), whereas SSE relies on TCP flow control and may buffer unboundedly on the client.
Summarize when to choose each: WebSockets for low-latency, bidirectional, high-frequency interactions; SSE for simpler, unidirectional, auto-reconnecting streams.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Rote stuff, but I always mix up layer 5 and 6.
Start by defining the OSI model as a conceptual framework for understanding network communication, then walk through each layer from top to bottom (or bottom to top) with a brief explanation of its primary function and a concrete example. Emphasize how this model helps in troubleshooting and system design, especially for a company like Snapchat that deals with real-time multimedia.
Pro tip: Relate each layer to real-world scenarios at Snapchat, such as how Snapchat's ephemeral messaging might leverage the session layer for managing connections or the presentation layer for media encoding. This shows you can apply theoretical knowledge to practical engineering problems.
Briefly explain that the OSI model is a 7-layer conceptual framework that standardizes network functions, aiding in design, troubleshooting, and interoperability.
Describe the top layers: Application (user services like HTTP), Presentation (data translation, encryption, compression), and Session (establishing, managing, and terminating sessions).
Explain the Transport layer's role in end-to-end communication, including segmentation, flow control, error recovery, and protocols like TCP and UDP.
Cover the Network layer (logical addressing, routing via IP), Data Link layer (physical addressing, framing, error detection via MAC), and Physical layer (transmission of raw bits over media).
Conclude by summarizing the model's benefits and discuss how it informs design decisions, such as choosing protocols or debugging network issues in a system like Snapchat.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by briefly explaining what QUIC is and its core design goals, then contrast it with TCP+TLS to highlight the specific problems it solves (e.g., head-of-line blocking, handshake latency). Finally, discuss real-world adoption, especially in large-scale consumer apps like Snapchat, to show practical awareness.
Pro tip: Mention that QUIC's user-space implementation allows faster iteration and deployment than kernel-based TCP, which is crucial for companies like Snapchat that need to rapidly optimize for mobile networks.
Briefly state that QUIC is a UDP-based transport protocol that integrates TLS 1.3 and aims to improve web performance. Mention it was standardized by IETF as RFC 9000.
Discuss issues like head-of-line blocking at the transport layer, multiple round trips for handshake (TCP + TLS), and inflexibility due to kernel implementation.
Cover QUIC's features: stream multiplexing without HOL blocking, 0-RTT/1-RTT handshake, connection migration, and user-space deployment.
Acknowledge that QUIC may have higher CPU usage due to user-space processing and that UDP may be blocked by some networks, requiring fallback.
Mention major adopters: Google (YouTube, Chrome), Facebook, Cloudflare, and Snapchat. Explain how QUIC benefits Snapchat's mobile-first, real-time communication needs.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Choose a project where you made significant technical decisions, and structure your answer using a clear narrative: context, problem, options considered, decision, and outcome. Focus on the 'why' behind each decision, emphasizing trade-offs and how you balanced them to meet requirements.
Pro tip: Quantify the impact of your decisions (e.g., latency reduction, cost savings) and relate them to Snapchat's scale and user experience. Show that you consider not just technical merit but also business and user impact.
Briefly describe the project, your role, and the goals. Keep it concise to leave time for technical depth.
Explain the specific technical challenge or requirement that necessitated making decisions.
Present 2-3 viable technical approaches, comparing their pros and cons (e.g., performance, scalability, complexity).
Describe which option you chose and justify it based on project constraints, data, and long-term implications.
Share the results, including metrics and lessons learned, and how it impacted the product or team.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.