Choosing a Real-Time Transport

You are designing three features and must pick a transport for each:

• A. A stock-ticker web page showing live prices for 20 symbols (updates several times per second, browser only, users never send data).
• B. A customer-support chat widget where the user and agent both type; must work through corporate proxies.
• C. An internal admin dashboard that shows the count of pending jobs; freshness within 30 seconds is fine.

1. Choose between short polling, long polling, SSE and WebSockets for each, and justify.
2. For feature A, estimate the connection state for 500,000 concurrent viewers if each connection costs ~20 KB of memory. How would you distribute the load, and how does new price data reach every connected client?
3. What operational issue does SSE have behind some reverse proxies, and how do you fix it?