Hi Undertow Team,
I just took a quick glimpse into Undertow, to be honest, as I was just evaluating it for a project. I planed to use it as a standalone reverse proxy including caching and SSI as an alternative to apache.
However, as far as I saw this is not yet a feature set available in Undertow. Anyway, I am not worried to get my hands dirty and add a bit of code myself, so I looked a bit closer onto the proxy example and the underlying classes.
As far as I saw it should be possible to add a CacheHandler in front of the ProxyHandler that just uses the proxy handler in case of a miss. However, I did not find a good way to hook into the Proxy Handler (it's also final :( ) to extend its functionality to store the response in the cache.