Server-side Apply is an important effort to migrate “kubectl apply” to the apiserver with a server-side implementation, permitting use by tools/clients other than kubectl.
Server-side Apply is a new merging algorithm, as well as tracking of field ownership, running on the Kubernetes api-server. Server-side Apply enables new features like conflict detection, so the system knows when two actors are trying to edit the same field.
Server-side Apply helps users and controllers manage their resources through declarative configurations. For more information you should follow this blog post
