Caching Infrastructure: You are retrofitting a web app without an existing caching tier. Suppose you want to add a server-side cache to improve performance. What are your options, and what are key considerations for each option? For example, when would you use Memcached vs. Redis vs. other solutions, and what factors would affect where in the stack you would implement caching?

Capacity Scenario: You run a web site that receives 1 million page views per day at its peak. The web site receives a sudden spike of traffic to triple its usual number of requests per minute. How would you handle this situation? Include steps you would take to analyze the influx of traffic and whether and how you would scale the web site to handle the traffic (e.g. add web servers). If you determine that the traffic increase is not legitimate (a DDOS attack, a runaway script hitting your site, etc.), how would you mitigate the traffic? Specify any assumptions you make about your stack and architecture.