Is CaaS a specific type of PaaS?
PaaS and CaaS are two different things.
On PaaS, you only run your code in a cartridge (which could be a virtual machine or even a container), but you will be able to run code supported by your PaaS provider. You cannot change the OS your code is running on. Example: Heroku
On CaaS, you will be able to run a container and you will not be limited to the languages supported by your PaaS provider. You can run whatever you want in your container as long as the container engine is supported by your CaaS provider. Example: Amazon Container Services (ECS)
CaaS sits somewhere between infrastructure as a service (IaaS) and platform as a service (PaaS).
Check it out for more information: http://searchitoperations.techtarget.com/definition/Containers-as-a-Service-CaaS
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