Hi Francois
I'm a CloudAfrica customer and very happy with their service. Hosting a couple of my clients there. Network performance can be a little lacklustre on the smallest instances but not restrictively so. Of course, Digital Ocean and Linode also offer great service (I use them both) although not local companies and their closest footprints are in Europe.
Hetzner (
hetzner.co.za) are unquestionably the best in South Africa for physical server hosting; facilities, infrastructure, service, pricing all excellent. You will need to get a self-managed dedicated server though for hosting RoR, perhaps too costly for a single client.
I would caution against some of the larger ISPs such as AfriHost (they use VMware and have a history of terrible outages) and MWEB (known for bad customer service).
Disclaimer: I used to work for Hetzner.