Can someone recommend a simple (possibly automated) hardness scan/check of a Debian 7 image on a Linode? Just something to check for basics, possibly with options for increased hardness checks for a higher cost.

A nice basic hardness check that I really like is Lynis (can do "apt-get install lynis" although repo might be a few minor versions out of date).

The next step after that is running an IDS. A really good choice here is OSSEC. This isn't overly complex and has a lot of benefit. Many of the other open source choices in this area, such as Tripwire, are a waste of time because they aren't maintained anymore (usually the developers are now focused on commercial enterprise versions).

If you want to check your SSL "hardness" a great free service is SSL Server Test by Qualys SSL Labs.

Beyond the open source stuff you can run free-trials, or community editions, of some of the better commercial tools. For example:

Qualys ExpressGuard Lite, Trial version will do external scan, internal system scan, and a web app scan (same guys who run the free SSL Server Test mentioned above).

Rapid7 Nexpose Community edition.

beyondtrust Retina CS Community Edition (I've never been able to test this tool because it requires a Windows server as the scan launcher).

Thanks. I take this to mean that it must be installed first.

Would there be any other option that does not need to be installed? IOW it would just make a "scan" from the outside?