Author here! This post is slightly out of date, as the server now does have a database to handle patron registration, and we've upgraded to 4GB because we needed more RAM to build the extremely long endnotes in Gibbon's Decline and Fall of the Roman Empire. But the server still indexes and serves ebooks in the same way!
Check out zram if you feel like 2GB should still be possible.
How does search work without a database?
I notice the URL has parameters called `query` and `sort`: