Day 99 of 100 Days :Advanced Kubernetes Concepts: Interview Questions and Answers
As you approach the final stretch of your 100 Days DevOps journey, it's time to dive deeper into more advanced Kubernetes topics. This set of interview questions will explore concepts like custom controllers, network policies, persistent storage, and more. These topics are critical for mastering Kubernetes and demonstrate a deeper understanding of managing complex applications at scale.
Here are 15 advanced Kubernetes interview questions and answers to elevate your knowledge:
1. What is a Custom Controller in Kubernetes?
A Custom Controller is a Kubernetes component that watches for changes to specific resources and takes actions to bring them into the desired state. Custom controllers are often built to manage resources that are not natively supported by Kubernetes, providing the ability to implement custom logic for specific workloads or business needs. They are often created with the Kubernetes Operator pattern.
2. What is the difference between a ReplicaSet and a Deployment?
Although both ReplicaSets and Deployments manage the number of pod replicas, the key difference is that a Deployment allows for rolling updates, rollback capabilities, and other advanced deployment strategies. A ReplicaSet on its own doesn't provide such features but simply ensures a specified number of pod replicas are running.
3. Explain the concept of Horizontal Pod Autoscaling (HPA).
Horizontal Pod Autoscaling (HPA) automatically adjusts the number of pods in a deployment or replica set based on observed CPU utilization or other custom metrics. The HPA ensures that the application is scaling based on demand, thereby maintaining performance without over-provisioning resources. It helps optimize resource usage and maintain application availability.
4. What are Network Policies in Kubernetes?
Network Policies are used to control the communication between pods in a Kubernetes cluster. By default, all pods can communicate with each other, but network policies allow you to define rules that restrict or allow traffic based on factors like pod selectors, namespaces, IP blocks, or ports. They provide a way to enhance security within a cluster by defining who can communicate with whom.
5. What is Persistent Volume (PV) and Persistent Volume Claim (PVC) in Kubernetes?
A Persistent Volume (PV) is a piece of storage that has been provisioned by an administrator or dynamically created by Kubernetes. A Persistent Volume Claim (PVC) is a request for storage by a user. The claim is matched to an available PV, and once bound, the PVC can be used by pods for persistent storage. PVs and PVCs enable stateful applications to maintain data across pod restarts or rescheduling.
6. What is a Kubernetes Operator?
A Kubernetes Operator is a method of packaging, deploying, and managing a Kubernetes application. Operators use custom resources and controllers to manage complex, stateful applications. They automate tasks such as backups, upgrades, and scaling, helping to reduce manual intervention in the lifecycle of an application.
7. Explain the concept of Init Containers in Kubernetes.
Init Containers are special containers that run before the main containers in a pod start. They are often used to perform setup tasks, such as initializing configuration, waiting for external services, or preparing shared volumes. Init Containers run sequentially, and only once they complete successfully will the main application containers start running.
8. What is a Kubernetes Ingress Controller?
An Ingress Controller is a component that manages external access to services within a Kubernetes cluster, often via HTTP or HTTPS. It listens for changes to Ingress resources and enforces routing rules. Popular ingress controllers include NGINX, Traefik, and HAProxy. They allow fine-grained control over the routing of external traffic to internal services based on paths or hostnames.
9. What are Taints and Tolerations in Kubernetes?
Taints and Tolerations are used to control pod placement on nodes in a Kubernetes cluster. Taints are applied to nodes to prevent certain pods from being scheduled on them unless the pod has a matching toleration. This is useful for scenarios like isolating certain workloads, ensuring that only specific types of pods run on certain nodes, or preventing specific pods from running on problematic nodes.
10. What is a Kubernetes Job and CronJob?
A Kubernetes Job ensures that a specified number of pods run to completion, and it is typically used for batch processing tasks like backups or one-time jobs. A CronJob is similar to a Job, but it allows you to run jobs on a scheduled basis, much like a cron job in Unix-based systems. CronJobs are useful for regular maintenance tasks like database cleanup or report generation.
11. What is the purpose of Kubernetes RBAC?
Role-Based Access Control (RBAC) in Kubernetes is a method for regulating access to resources based on roles. RBAC allows you to define what actions users or service accounts can perform on Kubernetes resources (e.g., Pods, Services, ConfigMaps). It provides fine-grained control over permissions, improving security and ensuring that only authorized users or services can perform specific actions.
12. What is the concept of Kubernetes Admission Controllers?
Admission Controllers are pieces of code that intercept requests to the Kubernetes API server before they are persisted in etcd. They can be used to enforce policies, validate input, and mutate resources before they are created or modified. Common examples include enforcing resource limits, ensuring proper labels are applied, or automatically injecting sidecars into pods.
13. What is the role of the Kubernetes Scheduler?
The Kubernetes Scheduler is responsible for selecting a node for a pod to run on. It takes into account resource availability, constraints like taints and tolerations, affinity/anti-affinity rules, and other factors such as pod priorities or custom scheduling policies. The Scheduler ensures that pods are placed on the best nodes based on their requirements and cluster resources.
14. What is the concept of Cluster Autoscaler in Kubernetes?
The Cluster Autoscaler automatically adjusts the size of a Kubernetes cluster based on the current resource usage. If the cluster is underutilized, it will scale down by removing nodes, and if the demand for resources increases (e.g., more pods need to be scheduled), it will scale up by adding more nodes. This feature helps manage resources efficiently and keep costs down in cloud environments.
15. What are Kubernetes Custom Resources and Custom Resource Definitions (CRDs)?
Custom Resources (CRs) are extensions of the Kubernetes API that allow you to define your own resource types. Custom Resource Definitions (CRDs) allow you to create these custom resources in your cluster. CRDs enable the use of Kubernetes-native tools (like kubectl) to manage non-standard resources, which is particularly useful when building applications using the Operator pattern.
Conclusion:
As you approach Day 100, these advanced Kubernetes concepts will deepen your understanding of how Kubernetes works at scale and how it can be leveraged to solve complex problems. Mastering these topics will set you apart as a proficient DevOps engineer capable of managing large, distributed systems efficiently. Keep exploring and experimenting with Kubernetes, as it's a tool that offers immense flexibility for cloud-native application management, and it’s essential for modern DevOps practices. You've come a long way—great work!