I have set up Apache 2.2 as a reverse proxy with the following configuration: # jBoss proxying ProxyRequests Off <Proxy *> Order deny,allow Allow from all </Proxy> ProxyPass /foo http://localhost:9080/foo ProxyPassReverse /foo http://localhost:9080/foo ProxyPassReverseCookiePath /foo /foo # Reverse proxy caching CacheEnable disk /foo # Compression SetOutputFilter DEFLATE BrowserMatch ^Mozilla/4 gzip-only-text/html BrowserMatch ^Mozilla/4\.0[678] no-gzip BrowserMatch \bMSIE\s(7|8) !no-gzip !gzip-only-text/html DeflateCompressionLevel 9 Header append Vary User-Agent env=!dont-vary However, in a number of cases where I expect a cached response to be returned the request is sent through to the origin server at localhost:9080. Responses have a HTTP Vary header of 'Accept-Encoding,User-Agent' which is to be expected given the mod_deflate configuration. How can I determine why Apache is unable to serve a response from the cache?