Lessons learned: 1) Keep it very simple 2) Don’t re-invent the wheel 3) Go with proven and solid technologies when you can.

Egads, Instagram only has 3 engineers.

Score another point for the all-Amazon-Web-Services-instead-of-hosting-ourselves team.

Also, this is interesting: Redis powers their main feed, activity feed, sessions system, and other services.

If Redis is good enough for Instagram and porn, it's good enough for anyone with scaling needs.

Well played, sirs.

By comparison, Tumblr uses a lot more bleeding edge technologies.

Co-founder Mike K just gave a 185-slide talk at Airbnb about scaling Instagram: http://techcrunch.com/2012/04/12/how-to-scale-a-1-billion-startup-a-guide-from-instagram-co-founder-mike-krieger/