It’s been mentioned before - I think Oracle is being naughty, giving you much less than 1G which they round up when describing it:
Edit: see the linked blog:
Perhaps most important missing instruction is don’t use the default server image . Discourse requires 1GB of RAM (or there abouts) and the Oracle Linux image doesn’t leave enough memory for some reason. I don’t know whether CentOS will work, but the Ubuntu image is fine. Just be sure to pick the full install2 rather than the “Minimal” install