[inoop]

The cost doesn't suddenly drop to zero once development is done. Typically a system of this complexity and scale requires constant maintenance. You'll need someone to be on-call (pager duty) to respond to alarms, you'll need to fix bugs, improve efficiency, apply security patches, tune alarms and metrics, etc.

In my experience you probably need a small team (6-8 people) to maintain something like this. Maybe you can consolidate some things (e.g. if your system has low on-call pressure, you may be able to merge rotations with other teams, etc.) but it doesn't go down to zero.

[shrubble]

If you follow the various links on the Uber site, you see that they have multiple applications sitting on the same database. see https://www.uber.com/blog/schemaless-sql-database/ . It's not just 1 design of a database, with 1 application on top...