Top 27 Kubernetes Interview Questions And Answers

Question 1

What is Kubernetes? Why organizations are using it?

Accepted Answer

**Kubernetes** is an open-source system for automating deployment, scaling, and management of containerized applications. To understand what Kubernetes is good for, let's look at some examples: * You would like to run a certain application in a container on multiple different locations. Sure, if it's 2-3 servers/locations, you can do it by yourself but it can be challenging to scale it up to additional multiple location.
* Performing updates and changes across hundreds of containers
* Handle cases where the current load requires to scale up (or down)

Question 2

What does a Pod do?

Accepted Answer

Pods represent the processes running on a cluster. By limiting pods to a single process, Kubernetes can report on the health of each process running in the cluster. Pods have:  
  
- a unique IP address (which allows them to communicate with each other)
- persistent storage volumes (as required)
- configuration information that determine how a container should run.

Although most pods contain a single container, many will have a few containers that work closely together to execute a desired function.

Question 3

What is a Kubernetes Cluster?

Accepted Answer

A **Kubernetes cluster** is a set of node machines for running containerized applications. If you’re running Kubernetes, you’re running a cluster. At a minimum, a cluster contains a **worker node** and a **master node**.

A **worker node** is a virtual machine or a physical server that serves as a worker for running the applications. It contains from:
  * Kubelet - an agent responsible for node communication with the master.
  * Kube-proxy - load balancing traffic between app components
  * Container runtime - the engine runs the containers (Podman, Docker, ...)

It's recommended to have at least 3 nodes in Kubernetes production environment.

The **master node** coordinates all the workflows in the cluster:

* Scheduling applications
* Managing desired state
* Rolling out new updates

Question 4

How can containers within a pod communicate with each other?

Accepted Answer

Containers within a pod share networking space and can reach other on `localhost`. For instance, if you have two containers within a pod, a MySQL container running on port `3306`, and a PHP container running on port `80`, the PHP container could access the MySQL one through `localhost:3306`.

Question 5

What is Kubernetes, exactly?

Accepted Answer

The purpose of **Kubernetes** is to make it easier to organize and schedule your application across a fleet of machines. At a high level it is an operating system for your cluster.

Basically, it allows you to not worry about what specific machine in your datacenter each application runs on. Additionally it provides generic primitives for health checking and replicating your application across these machines, as well as services for wiring your application into micro-services so that each layer in your application is decoupled from other layers so that you can scale/update/maintain them independently.

Question 6

What is a Pod?

Accepted Answer

**Pods** are the smallest, most basic deployable objects in Kubernetes. A Pod represents a single instance of a running process in your cluster.

Pods contain one or more _containers_, such as Docker containers. When a Pod runs multiple containers, the containers are managed as a single entity and share the Pod's resources. Pods also contain shared networking and storage resources for their containers

Question 7

Explain when to use Docker vs Docker Compose vs Docker Swarm vs Kubernetes

Accepted Answer

* **Docker** is a container engine, it makes you build and run usually no more than one container at most, locally on your PC for development purposes.
* **Docker Compose** is a Docker utility to run multiple containers and let them share volumes and networking via the docker engine features, runs locally to emulate service composition and remotely on clusters. Docker Compose is mostly used as a helper when you want to start multiple Docker containers and don't want to start each one separately using `docker run ...`.
* **Docker Swarm** is for running and connecting containers on _multiple_ hosts. It does things like scaling, starting a new container when one crashes, networking containers.
* **Kubernetes** is a container orchestration platform, it takes care of running containers and enhancing the engine features so that containers can be composed and scaled to serve complex applications (sort of PaaS, managed by you or cloud provider). Kubernetes' goal is very similar to that for Docker Swarm but it's developer by Google.

Question 8

Explain what are some Pods usage patterns?

Accepted Answer

Pods can be used in two main ways:

- **Pods that run a single container.** The simplest and most common Pod pattern is a single container per pod, where the single container represents an entire application. In this case, you can think of a Pod as a wrapper.
- **Pods that run multiple containers that need to work together.** Pods with multiple containers are primarily used to support colocated, co-managed programs that need to share resources. These colocated containers might form a single cohesive unit of service—one container serving files from a shared volume while another container refreshes or updates those files. The Pod wraps these containers and storage resources together as a single manageable entity.

Each Pod is meant to run a single instance of a given application. If you want to run multiple instances, you should use one Pod for each instance of the application. This is generally referred to as _replication_. Replicated Pods are created and managed as a group by a controller, such as a Deployment.

Question 9

Which problems does a _Container Orchestration_ solve?

Accepted Answer

Containers run in an isolated process (usually in it's own [namespace](https://www.toptal.com/linux/separation-anxiety-isolating-your-system-with-linux-namespaces)). This means that by default the container will not be aware of other containers. Additionally, it will not be aware of the systems files, network interfaces, and processes. While this can greatly help with portability of the software it does not solve several production issues such as [microservices](https://en.wikipedia.org/wiki/Microservices), container discovery, scalability, disaster recovery, or upgrades.

**Adding a container orchestrator can greatly reduce the complexity** in production as these tools are designed to resolve the issues outlined above. For example, Kubernetes is built to allow containers to be linked together, deploy containers across an entire network, scale and load balance the network based on container resource consumption, and allow upgrades of individual containers with no downtime.

If you are only running a single container or two containers together you are correct in that an orchestrator may be unnecessary and add unneeded complexity.

Question 10

What are the benefits of a Pod?

Accepted Answer

When pods contain multiple containers, _communications_, and _data sharing_ between them is simplified. Since all containers in a pod share the same network namespace, they can locate each other and communicate via localhost. Pods can communicate with each other by using another pods IP address or by referencing a resource that resides in another pod.

Pods can include containers that run when the pod is started, say to perform initiation required before the application containers run. Additionally, pods simplify scalability, enabling _replica_ pods to be created and shut down automatically based on changes in demand.

Top 27 Kubernetes Interview Questions

What is Kubernetes? Why organizations are using it?

What is a Kubernetes Cluster?

What is a Pod?

How can containers within a pod communicate with each other?

What does a Pod do?

What is Kubernetes, exactly?

What happens when a master fails? What happens when a worker fails?

What are namespaces? What is the problem with using one default namespace?

What does it mean that "pods are ephemeral"?

What is a DaemonSet?

Why may you have Pod is in a Pending state?

What is an Ingress Controller?

Explain what is a Master Node and what component does it consist of?

When to use StatefulSet?

What is a StatefulSet in Kubernetes?

What are the benefits of a Pod?

Explain what are some Pods usage patterns?

Which problems does a Container Orchestration solve?

Explain when to use Docker vs Docker Compose vs Docker Swarm vs Kubernetes

What is the difference between Kubernetes and Docker?

How does Kubernetes use etcd?

How to rollback a Deployment?

Why do we need Kubernetes (and other orchestrators) above containers?

How does StatefulSets use differ from the use of "stateless" Pods with Persistent Volumes?

How do I build a High Availability (HA) cluster?

Can you explain a relationship between container runtime and container orchestration?

Explain what are Taints in Kubernetes?