Is the course enough for the CKA

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Having taken the exam I would say the course is a very good start toward certification. The course is not dedicated to the exam. If you are knowledgeable and experienced as a Kubernetes admin you will have a good chance of passing. It is 100% practical, so you will need to know and be quick to preform administrative tasks.

I would encourage you to write out and practice each of the steps listed in the CNCF guide, as the allotted exam time goes by very fast. I would say if you can complete each bullet point without having to look up the steps, and can check your own work you are in a good place.  

https://github.com/cncf/curriculum/blob/master/certified_kubernetes_administrator_exam_v1.9.0.pdf