Conquer the CKAD Challenge 2025: Unleash Your Kubernetes Power!

To ensure only one instance of a pod runs in a Kubernetes environment, using a Deployment with a replica count set to one is the most effective method. A Deployment resource in Kubernetes manages a set of identical pods, ensuring that the specified number of pod replicas is running at any given time. By setting the replica count to one, you are explicitly instructing the Kubernetes control plane to maintain exactly one pod instance. If that pod fails or is terminated for any reason, the Deployment controller will automatically create a new instance, thereby ensuring continuity with a single running pod.

The other options do not provide a reliable solution for ensuring that only one instance of a pod is active. A Service does not control the number of pods; it merely provides a stable endpoint for accessing them. Using a ConfigMap does not impact pod creation directly and is mainly used for configuring application settings. Having multiple Deployments with varying replicas would actually result in multiple pod instances running concurrently, which contradicts the goal of limiting to a single pod instance.

This understanding is crucial for managing resources and ensuring proper application behavior in a Kubernetes environment.