Log into EC2 instance on Amazon AWS.

Edit the /etc/nginx/nginx.conf file to add the following within the sever {} object:

gzip            on;
gzip_comp_level  4; # or whatever you want
gzip_types    text/plain application/javascript application/x-javascript text/javascript text/xml text/css;

Then restart nginx: service nginx restart

Thanks to: https://stackoverflow.com/questions/23939722/nginx-gzip-not-compressing-javascript-files