Certified Kubernetes Application Developer (CKAD) Practice Test

Why are StatefulSets used in Kubernetes?

1. For load balancing across multiple Pods

2. To manage Pods with stable and unique network identifiers

3. To deploy stateless applications efficiently

4. For rapid scaling of identical Pods

The correct answer is: To manage Pods with stable and unique network identifiers

StatefulSets are a special type of workload controller in Kubernetes designed primarily for managing stateful applications. The correct choice highlights the unique capabilities of StatefulSets, particularly their ability to provide stable and unique network identifiers for Pods and maintain persistent storage. StatefulSets ensure that each replica of an application maintains its identity through a consistent naming convention and stable network address. Each Pod in a StatefulSet is assigned a unique ordinal index and retains the same hostname even if it is restarted or rescheduled. This feature is crucial for applications requiring stable connections, such as databases, where each instance needs to address dependencies and maintain a consistent state over time. In contrast, load balancing across multiple Pods typically relies on Services, which distribute traffic without regard to the unique identities of the Pods. Deploying stateless applications more efficiently is a function more suited to Deployments, which focus on identical replicas that can be created or destroyed without impacting the overall application state. Rapid scaling of identical Pods aligns with the capabilities of Deployments as well, which can quickly adjust the number of Pods based on load. Thus, the primary role of StatefulSets is indeed to manage Pods that require stable and unique network identifiers, fulfilling a critical need in Kubernetes for stateful applications.