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Hi, have you configured AWS security groups? Check here if you don't know how to do.

If you have configured it and the panel still not reachable give us some information like:
- Your OS

- Ajenti log ( /var/log/ajenti )

I think it's a good idea but i don't know if a complete change is the correct way to implement it, probably PHP and HHVM can work both on the same server, so i think that the user can select on "Content" tab what script he like to use

Sure!
Here you can find my backup script for file and here for mysql

I use it on crontab