set the thread _id as an index on the comment table, remove the array from the Thread model, alter endpoints accordingly

this will fix an issue where very large threads slow down queries that select them

and use the current if not set

applying sorting to getThreads increases query time by 100-200% on large collections (million+ comments). Adding an index helps but we should optimise this for at least the default sorting (last comment time).

use AOP / mongoose middleware to hook it into the post of a save operation

is the main bottleneck on threads calls now, move this to a separate record and manage it with the application?

This is 2013. Use SHA-2, PBKDF2, etc... Use an individual salt for each password!

holding the cache in memory means it needs to be cleaned regularly, may as well store the cache in a mongo collection and never have it expire

Possibly:

/user/:username/profile

don't think we'll need a summary version. Needs to return all the info required for the user profile page, and I guess we should strip out participated, favourites etc from the user document to cut down on the returned JSON size.

in https://github.com/cham/TeslaAPI/blob/master/src/db/db.js
instead of localhost, use process.env.mongoHost
and so on for username/pw/port

The API server should have these env variables configured during provisioning
MongoDB should eventually be hosted on its own server/vm/container
This way you can scale to multiple API servers since the db server is not hosted locally