The first thing that’s done in either case is to query a lookup table that has (at least) two columns: website id, and server id. This is the table that keeps track of what websites are on what database servers. The server id’s correspond to connection names in the databases.yml file, so the script can connect to the correct database to record a visit or generate a report.

It’s basic horizontal partitioning of the database. The table structures on each DB server are identical, so it’s just a matter of knowing which server has the rows you’re looking for. A few functions have to connect to every database to generate their report, like the summary screen shown after login that lists all websites in an account and some basic stats for each, as a user’s websites may be spread across multiple servers. In that case it’s just a loop over all the databases in the config file.