When I had an IaaS modeled hosting environment I wanted to utilize a CDN (CloudFlare) and I was required by the hosting company staff to point the name servers in my domain registrar to those of CloudFlare (instead to those of the hosting provider).
When I had a PaaS modeled hosting environment I wanted to utilize a CDN (CloudFlare) and I was not required by the hosting company staff to point the name servers in my domain registrar to those of CloudFlare.
Rather I was told that just enabling the CloudFlare option and configuring it correctly would be enough. I did so and went to the CloudFlare diagnostic center and there I found an error about nameservers.
I have inquired the PaaS modeled hosting provider's staff why the aforementioned error isn't a problem and a staff member replied something like:
We are direct partners with Cloudflare and we have made it possible to use Cloudflare with only two records that are updated on our end which are Cname and WWW.
I believe the staff member was wrong in thinking the WWW redirects are by themselves a Cname DNS record but here I just seek to learn why in the IaaS scenario I had to change nameservers and in the PaaS scenario I didn't have to and the staff member's reply didn't really explained that at all.