There is no difference between these two Kubernetes certification only difference in the advancement, which is listed here, also you can know more difference with this blog about the advantage and values of this blogs.
The main difference between these two exams is that CKA tests not only require knowledge of Kubernetes API primitives. The CKA exam also has things related to Kubernetes internals such as etcd, tls bootstrap, and kubelet.
The purpose of the Certified Kubernetes Administrator (CKA) program is to provide assurance that CKAs have the skills, knowledge, and competency to perform the responsibilities of Kubernetes administrators.
While CKAD is solely dedicated to concepts such as Deployments, DaemonSets, Pods, and other API primitives, we can consider it as a lightweight version of a CKA exam.
The Certified Kubernetes Application Developer exam certifies that users can design, build, configure, and expose native cloud applications for Kubernetes.
Not having difficult topics related to cluster administration does not make CKAD easier. You only get 2 hours to complete the test, while the CKAD allows 3 hours. During the CKA exam, I had some time to go over the results, while during the CKAD, I didn’t have enough time to complete all the tasks.
For an organization, having three or more CKA’s is a requirement to become a Kubernetes Certified Service Provider. CKAD doesn’t count towards this requirement. So, if your company is willing to become a Kubernetes Certified Service Provider — the CKA exam is your choice.