NGINX: upstream timed out (110: Connection timed out) while reading response header from upstream

For my case, I got around this issue by clearing the connection keep-alive flag and specifying http version as per the answer here: 

https://stackoverflow.com/a/36589120/479632

server {
    location / {
        proxy_set_header   X-Real-IP $remote_addr;
        proxy_set_header   Host      $http_host;

        # these two lines here
        proxy_http_version 1.1;
        proxy_set_header Connection "";

        proxy_pass http://localhost:5000;
    }
}