Kubectl

Kubernetes - Kubectl

• It is a command-line tool that allows you to run commands against Kubernetes clusters.

Deploying Images

• To deploy an image to a Kubernetes cluster, use kubectl create deployment. (Since v1.18, kubectl run only creates a single bare Pod, not a Deployment, so nothing recreates it if it dies.)

kubectl create deployment <deployment-name> --image=<image-name>
 
# single Pod only (useful for quick tests)
kubectl run <pod-name> --image=<image-name>

• Example:

kubectl create deployment synergychat-web --image=docker.io/bootdotdev/synergychat-web:latest

Get all Deployments

kubectl get deployments

Get all Pods

• Pods are the smallest deployable units 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.
• A pod is an abstraction over a container, and remember, a container is just a running instance of an image. To oversimplify, a pod is a running application.

kubectl get pods

• To get wide output, you can use the -o wide flag.

kubectl get pods -o wide

Edit a Deployment

• To edit a deployment, you can use the kubectl edit command.

kubectl edit deployment <deployment-name>

Delete a Deployment

• To delete a deployment, you can use the kubectl delete command.

kubectl delete deployment <deployment-name>

Delete a Pod

• To delete a pod, you can use the kubectl delete command.

kubectl delete pod <pod-name>

Get all ConfigMaps

• ConfigMaps are a Kubernetes resource that allows you to store configuration data in key-value pairs.
• ConfigMaps allow you to decouple your configurations from your container images.

kubectl get configmaps

Apply a ConfigMap

• To apply a ConfigMap, you can use the kubectl apply command.

kubectl apply -f <configmap-file>

Get all Services

• A Kubernetes Service is an abstraction which defines a logical set of Pods and a policy by which to access them.
• Services enable a loose coupling between dependent Pods.

kubectl get services

Get all Nodes

• A node is a worker machine in Kubernetes.
• A node may be a VM or physical machine, depending on the cluster.
• Each node has the services necessary to run pods and is managed by the control plane.

kubectl get nodes

Get all Namespaces

• A namespace is a way to divide cluster resources between multiple users.
• It is a way to divide cluster resources between multiple users.

kubectl get namespaces

Port Forwarding

• To forward a port from a Kubernetes pod to your local machine, you can use the kubectl port-forward command.

kubectl port-forward <pod-name> <local-port>:<pod-port>

Proxy

• To access the Kubernetes API server, you can use the kubectl proxy command.

kubectl proxy

Replica Sets

• A ReplicaSet ensures that a specified number of pod replicas are running at any given time.
• A ReplicaSet is defined with a spec that specifies how many replicas it should maintain.

kubectl get replicasets

Distributed Systems

Whenever you’re dealing with a system that involves multiple machines talking to each other over a network, you’re dealing with a distributed system. Distributed systems are inherently complex, and Kubernetes is no exception, but that complexity is generally abstracted away from you as a K8s user. That’s what makes Kubernetes so cool! It does a lot of the hard work for you.

• A distributed system is a system whose components are located on different networked computers, which communicate and coordinate their actions by passing messages to one another.
• The components interact with one another in order to achieve a common goal.
• Distributed systems are designed to improve performance and scalability.
• They are also more fault-tolerant than centralized systems.
• Distributed systems are used in many applications, such as cloud computing, big data processing, and social networks.
• Examples of distributed systems include the Internet, Google’s search engine, and Amazon’s e-commerce platform.

Resource and Nodes

• Resource: A resource is an object that Kubernetes manages. For example, a pod is a resource.
• Node: A node is a worker machine in Kubernetes. It may be a VM or physical machine, depending on the cluster. Each node has the services necessary to run pods and is managed by the control plane.

Note: Kubernetes manages the resources that applications require and automatically distributes the load across nodes