Connecting to mongodb using mongoose and Fixie (Heroku add-on)
Just got a reply from Fixie's team:
Fixie is an http/https proxy, so it won't work for lower-level TCP connections like you'd need for your mongodb connection
When I asked about the possibility of using SOCKS for this case, they replied:
It looks like mongoose does not natively support socks proxies, and it does not accept a custom socket (which is how Node database drivers for MySQL and Postgres support it).
So apparently, in my case, there is no way to establish a connection to MongoDB Atlas cluster using mongoose through the proxy solution offered by Fixie (Heroku Add-on).