Day 37: Kubernetes Important Questions.

Questions:

What is Kubernetes and why it is important?

• Kubernetes is an open-source container orchestration tool developed by Google to manage containerized applications in different types of environments such as physical, virtual, and cloud infrastructure. It is used to automate the deployment, scaling, and management of containerized applications.

• Kubernetes is important because it allows you to deploy containerized applications to a cluster without tying them specifically to individual machines. Kubernetes automates the distribution and scheduling of application containers across a cluster in a more efficient way.

  What is the difference between docker swarm and Kubernetes?

• Docker Swarm is a container orchestration tool, meaning that it allows the user to manage multiple containers deployed across multiple host machines. Kubernetes is also a container orchestration tool. However, it is more extensive than Docker Swarm and is more popular as well.

• Docker Swarm is a native clustering or orchestration tool for Docker. It allows us to create and access a pool of Docker hosts using the full suite of Docker tools. Kubernetes is an open-source container orchestration tool developed by Google.

• Docker Swarm is easy to set up and use. Kubernetes is complex to set up and use.

• Docker Swarm is less secure than Kubernetes. Kubernetes is more secure than Docker Swarm.

• Docker Swarm is less scalable than Kubernetes. Kubernetes is more scalable than Docker Swarm.

• Docker Swarm is less flexible than Kubernetes. Kubernetes is more flexible than Docker Swarm.

• Docker Swarm is less portable than Kubernetes. Kubernetes is more portable than Docker Swarm.

• Docker Swarm is less efficient than Kubernetes. Kubernetes is more efficient than Docker Swarm.

  How does Kubernetes handle network communication between containers?

• Kubernetes uses kube-proxy to handle network communication between containers. Kube-proxy is a network proxy that runs on each node in the cluster. It maintains network rules on nodes. These network rules allow network communication to your Pods from network sessions inside or outside of your cluster.

• Kube-proxy uses the iptables utility to set up rules for handling network operations. Kube-proxy sets up rules to forward all traffic to Services (that have the type=NodePort or type=LoadBalancer).

  How does Kubernetes handle the scaling of applications?

• Kubernetes lets you automate many management tasksinclude provisioning and scaling.

• The Kubernetes autoscaling mechanism uses two layers:

1. Pod-based scaling—supported by the Horizontal Pod Autoscaler (HPA) and the newer Vertical Pod Autoscaler (VPA).

2. Node-based scaling— supported by the Cluster Autoscaler.

• Horizontal Pod Autoscaler (HPA):

1. When the level of application usage changes, you need a way to add or remove pod replicas. Once configured, the Horizontal Pod Autoscaler manages workload scaling automatically.

2. The Horizontal Pod Autoscaler (HPA) automatically scales the number of pods in a replication controller, deployment, replica set or stateful set based on observed CPU utilization (or, with custom metrics support, on some other application-provided metrics).

• Vertical Pod Autoscaler (VPA):

1. The Vertical Pod Autoscaler (VPA) frees you from having to think about the resource requirements your containers. It automatically sets the resource requirements for your containers based on usage patterns.

2. Some workloads can require short periods of high utilization. Increasing request limits by default would entail wasting unused resources, and would limit the nodes that can run those workloads.

• Cluster Autoscaler:

1. The Cluster Autoscaler automatically adjusts the number of nodes in a cluster when pods fail to launch due to lack of resources in the cluster. It can also scale down the number of nodes in the cluster if nodes are underutilized and their pods can be freed up by being moved onto other nodes in the cluster.

   What is a Kubernetes Deployment and how does it differ from a ReplicaSet?

• A ReplicaSet is a Pod controller that ensures a specified number of Pod replicas are running at any given time. However, a ReplicaSet does not guarantee that a Pod is scheduled onto a node. To guarantee that a Pod is scheduled, you can use a Deployment.

• A Deployment is a higher-level concept that manages ReplicaSets and provides declarative updates to Pods along with a lot of other useful features. Therefore, you should use Deployments instead of ReplicaSets.

  Can you explain the concept of rolling updates in Kubernetes?

• Rolling updates allow Deployments update to take place with zero downtime by incrementally updating Pods instances with new ones. The new Pods will be scheduled on Nodes with available resources.

  How does Kubernetes handle network security and access control?

• Networking is a particular complex part of Kubernetes. Networks can be configured in a variety of ways. You might use a service mesh, but you might not. Some resources in your cluster may interface only with internal networks, while others require direct access to the Internet. Ports, IP addresses, and other network attributes are usually configured dynamically, which can make it difficult to keep track of what is happening at the network level.

• Network policies define rules that govern how pods can communicate with each other at the network level.In addition to providing a systematic means of controlling pod communications, network policies offer the important advantage of allowing admins to define resources and associated networking rules based on contexts like pod labels and namespaces. Access COntrol:

• Access control in Kubernetes involves authentication and authorization mechanisms.

• RBAC, roles, and role bindings are used for defining permissions.

• Cluster roles and bindings provide global-level access control.

• Admission controllers validate and enforce access policies.

• Security contexts and auditing enhance security and accountability.

  Can you give an example of how Kubernetes can be used to deploy a highly available application?

• Kubernetes achieves high availability for applications by using features such as replication, scaling, pod anti-affinity, health checks, self-healing, service discovery, load balancing, and persistent storage. These features distribute the workload, monitor application health, ensure uninterrupted service, balance traffic, and maintain data integrity, resulting in a highly available application deployment.

  What is a namespace in Kubernetes? Which namespace any pod takes if we don't specify any namespace?

• In Kubernetes, a namespace is virtual cluster within a physical cluster. It provides a way to divide and segregate resources objects, such as pods, services, and deployments, into distinct groups. Namespaces are primarily used to create logical boundaries and enable multi-tenancy in a Kubernetes cluster.

• If you don't specify a namespace for a pod, it will be created in the default namespace. The default namespace is the initial namespace created by Kubernetes, and if no specific namespace is specified, all objects are assumed to belong to this default namespace.

• **Note:**It's worth noting that you can create and use custom namespaces to organize and manage resources based on your requirements, enabling better isolation and resource allocation within the cluster.

  How Ingress helps in Kubernetes?

• Ingress acts as a traffic controller and load balancer in Kubernetes.

• It provides external access services running within the cluster.

• Ingress enables routing of incoming traffic based on host, path, or other criteria.

• It supports load balancing to distribute traffic across multiple backend services.

• Ingress allows for TLS termination, handling SSL/TLS encryption at the edge.

• It simplifies the management and exposure of multiple services behind a single entry point.

  Explain different types of services in Kubernetes.

• A Kubernetes Service is an abstraction which defines a logical set of Pods running somewhere in your cluster, that all provide the same functionality. When created, each Service is assigned a unique IP address (also called clusterIP).

• This address is tied to the lifespan of the Service, and will not change while the Service is alive. Pods can be configured to talk to the Service and know that communication to the Service will be automatically load-balanced out to some pod that is a member of the Service.

Types of Services in Kubernetes:

• Visual Representation of Services in Kubernetes:

1. Can you explain the concept of self-healing in Kubernetes and give examples of how it works?

• Auto-Healing : Auto-healing is a feature that allows Kubernetes to automatically restart containers that fail for various reasons. It is a very useful feature that helps to keep your applications up and running.

• Auto-Scaling : Auto-scaling is a feature that allows Kubernetes to automatically scale the number of pods a deployment based on the resource usage of the existing pods.

Here on purpose, I have killed the pod to check the auto-healing feature. for Auto scaling we use replica set.

How does Kubernetes handle storage management for containers?

• A PersistentVolume (PV) is a piece of storage in the cluster that has been provisioned by an administrator or dynamically provisioned using Storage Classes.

• It is a resource in the cluster just like a node is a cluster resource. PVs are volume plugins like Volumes, but have a lifecycle independent of any individual Pod that uses the PV.

• This API object captures the details of the storage implementation, be that NFS, iSCSI, or a cloud-provider-specific storage system.

• A PersistentVolumeClaim (PVC) is a request for storage by a user. It is similar to a Pod. Pods consume node resources and PVCs consume PV resources. Pods can request specific levels of resources (CPU and Memory). Claims can request specific sizes and access modes (e.g., they can be mounted ReadWriteOnce, ReadOnlyMany or ReadWriteMany, see AccessModes.)

  How does the NodePort service work?

• A NodePort service in Kubernetes exposes a specific port of service to the outside world.

• Each worker node in the cluster listens on the assigned NodePort and forwards incoming traffic to the service.

• NodePort services are assigned a random port from the range 30000-32767.

• External clients access the NodePort service using the node's IP address or hostname along with the assigned NodePort.

• Load balancing is automatically handled across worker nodes hosting the service.

• Security measures like firewall rules or network policies should be implemented to control access and ensure security.

  What is a multinode cluster and a single-node cluster in Kubernetes?

• Multinode Cluster: A multinode cluster consists of multiple worker nodes a control plane. Each worker node is a separate physical or virtual machine that runs containerized applications. The control plane, typically consisting of multiple master nodes, manages and orchestrates the worker nodes. A multinode cluster offers scalability, high availability, and fault tolerance as the workload is distributed across multiple nodes.

• Single-Node Cluster: A single-node cluster, as the name suggests, comprises only one worker node a control plane. Both the worker node and control plane run on the same physical or virtual machine. In this setup, all Kubernetes components and the workload are running on a single node. A single-node cluster is often used for development, testing, or learning purposes when you don't require the full capabilities of a multinode cluster.

  Difference between "create" and "apply" in Kubernetes?

• kubectl apply is used to create and update a resource in Kubernetes. If the resource does not exist, it will be created. If the resource already exists, it will be updated with the new configuration.

• kubectl create is used to create a resource in Kubernetes. If the resource already exists, it will throw an error.

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Happy Learning :)