TCP proxy to postgres database as an upstream server in nginx

The issue was the "http://database_server" it is a tcp stream so you need to just proxy_pass database_server

also keep alive is not a directive that goes in a tcp upstream server

Here's an nginx configuration that worked for me (I'm running inside Docker, so some of these options are to help with that):

worker_processes auto;

daemon off;

error_log stderr info;

events {
    worker_connections 1024;
}

stream {
    upstream postgres {
        server my_postgres:5432;
    }

    server {
        listen 5432 so_keepalive=on;
        proxy_pass postgres;
    }
}

The key for me was the line listen 5432 so_keepalive=on;, which turns on TCP keepalive. Without that, I could connect but my connection would get reset after a few seconds.