Mongoldb over http via nginx (stream) reverse proxy - ruby-on-rails

Question

I am wanting to move a hosted mongo database service to a self hosted solution, behind a firewall. The hosted ruby on rails app connects via MongoMapper. I want to port only the database first, and then maybe the ruby on rails app.
I've set up server_name data.example.com port 80 on nginx 1.9.11 to redirected to another upstream port, localhost:8090.
This is done as I also have this nginx serve a website example.com:80 and www.example.com:80, but I only want data.example.com:80 to connect to the upstream tcp port. I do this as server_name is http section only, i.e. understandably not available in the stream server set-up)
so the "data-web-domain":80 to localhost:8090 config:
server {
listen 80;
server_name data.example.com;
location / {
proxy_pass http://localhost:8090;
}
Now I then pass localhost:8090 to mongodb via stream to allow tcp connection.
stream {
server {
listen 8090;
proxy_connect_timeout 1s;
proxy_timeout 3s;
proxy_pass stream_mongo_backend;
}
upstream stream_mongo_backend {
server localhost:27017;
}
}
and can browse to as data.example.com
Blockquote
You are trying to access MongoDB on the native driver port. For http diagnostic access, add 1000 to the port number
Ok so the above config allows a web request at the web domain to return an error message back from the mongodb
When connecting to the server directly, via localhost or the server's unix domain name to the port 8090 the stream redirect to 27017 works, i.e. this mongo command line connects
mongo server-unix-name:8090/dummydb -udummyuser -pdummysecret
But via the web domain doesn't
mongo data.example.com:80/dummydb -udummyuser -pdummysecret
What's broken between the data.example.com:80 to the localhost:8090?