Comprehensive and Detailed Explanation From General Kubernetes Knowledge:

Since this question involves AWS EKS and Azure AKS specifics outside the NKP context, and web search is unavailable, I will rely on general Kubernetes knowledge as of my last update. Using a custom image for EKS and AKS worker nodes means replacing the default, optimized images provided by AWS and Azure, which are pre-configured with components tailored for their managed Kubernetes services.

The primary functionality lost by using a custom image in both EKS and AKS is built-in autoscaling and security capabilities (Option C):

Autoscaling: Both EKS and AKS rely on their default node images to integrate with their native autoscaling mechanisms, such as the EKS Cluster Autoscaler (which uses AWS Auto Scaling Groups) and AKS Cluster Autoscaler (which integrates with Azure Virtual Machine Scale Sets). Custom images may lack the necessary agents or configurations (e.g., AWS SSM Agent, Azure VM extensions) to communicate with these autoscaling services, requiring manual configuration.

Security Capabilities: Default images include pre-configured security features, such as AWS’s integration with IAM roles for service accounts (IRSA) and Azure’s integration with Azure Active Directory (AAD) for RBAC. Custom images may not include these integrations, potentially breaking security features like automatic credential rotation or managed identity support unless manually configured.

Incorrect Options:

A. Native monitoring tools, logging, and alerting: Monitoring and logging (e.g., AWS CloudWatch, Azure Monitor) are managed at the control plane level, not the node image level, so these features are generally unaffected by custom images.

B. Cluster networking and load balancing: Networking (e.g., AWS VPC CNI, Azure CNI) and load balancing (e.g., AWS ALB, Azure Load Balancer) are configured by the control plane and CNI plugins, not the node image.

D. Ability to use GPUs and persistent storage: GPU support and persistent storage (e.g., EBS, Azure Disk) depend on drivers and CSI plugins, which can be installed on custom images without losing functionality.