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Can someone elaborate/clarify this:

> Users connect to a web tier which talks to an application tier.

So, I'm assuming the web tier is nginx/haproxy and the application tier is Pylons.

Are the 240 servers mentioned all running both the web tier and the app tier?

Presumably the web tier does slightly more than just reverse proxying. For example, it could build (render) pages based on an internal RedditAPI it queries. This RedditAPI (application layer) would then basically be a distributed database front-end with some state, like user sessions.

Seperating it at that point allows the web tier to offload much of the work (mostly rendering), while keeping it stateless, thus allowing effortless scaling of that tier.

No. Some are postgres, some are cassandra, some are web servers (haproxy), some are app servers (the reddit app running inside of pylons), etc

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