Azure Kubernetes Service (AKS) simplifies deploying a managed Kubernetes cluster in Azure by offloading the operational overhead to Azure. As a hosted Kubernetes service, Azure handles critical tasks, like health monitoring and maintenance.
Since Kubernetes masters are managed by Azure, you only manage and maintain the agent nodes. Therefore, Azure Kubernetes Service is free. You only pay for the agent nodes within your clusters, not for the masters.
Here is a simplified diagram providing an overview of what Azure Manage and what the customer manages.