I've setup a solr server in aws. It's an ubuntu server and jetty is the webserver being used. I'm able to access the solr instance externally but my webserver can't access the solr instance via the internal ip even though they are both part of the same default security group. I had a bit of trouble accessing the instance at all but I was able to finally get access externally by setting JETTY_HOME=0.0.0.0 in /etc/default/jetty (leaving it blank as instructed didn't seem to work). Netstat shows tcp6 0 0 :::8080 :::* LISTEN
Do you have port 8080 open explicitly for the default group? You should have two entries for 8080 - one for 0.0.0.0/0 and one for the security group itself.