Cheatography
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BasicsDefine :it is a container management technology developed by GOOGLE (later made open source in 2015) to manage containerized application(orchestration). |
Why1.Service discovery and load balancing 1.Service discovery and load balancing | 2.Automated rollbacks | 3.Self-healing | 4.Auto Scaling | 5.Canary updates and Rolling updates | 6.Open source & Community driven | 7.High Availability |
Kubernetes ConceptsNode | machine in the cluster | Docker | helps in creation of containers that includes apps and its binaries. | Pods | A Pod is the basic building block of Kubernetes–the smallest and simplest unit in the Kubernetes object model that you create or deploy,is also a group of containers (1 or more).Only containers of same pod can share shared storage. | Service | is an abstraction which defines a logical set of Pods and a policy by which to access them. | Jobs | Creates pod(s) and ensures that a specified number successfully completed.When a specified number of successful run of pods is completed, then the job is considered complete. | Cronjob | job scheduler in K8s | Replicasets | ensures how many replica of pod should be running. | Namespaces | Logical seperation between teams and thier environments.It allows various teams(Dev,Prod) to share k8s cluster by providing isolated workspace. | Deployment | Desired state of pods for declarative updates | daemonset | ensures a particular pod to be run on some or all nodes | persistentvolume | Persistent storage in the cluster with an independent lifecycle. | persistentvolumeclaim | Request for storage (for a PersistentVolume) by a user | ingress | An Ingress is a collection of rules that allow inbound connections to reach the cluster services. |
Namespaceskubectl get all --all-namespaces | shows all objects of all namespaces | kubectl get pods --all-namespaces | shows pods of all namespaces | kubectl get pods -n <name space> | shows pods of a namespace eg.kubectl get all -n kube-system :shows objects of system name space |
kubectl get namespaces (show all namspaces)
default:default name spaces of user
kube-public:Namespace for resources that are publicly available/readable by all
kube-system:Namespace for objects/resources created by Kubernetes systems | | Components Architecture Diagram
Components BasicComponents in Manager Nodes:
Controller manager: Runs various controllers to help move running state to desired state.
Node Controller: Responsible for noticing and responding when nodes go down.
Replication Controller: Responsible for maintaining the correct number of pods for every replication controller object in the system.
Endpoints Controller: Populates the Endpoints object (i.e, joins Services & Pods).
Service Account & Token Controllers: Create default accounts and API access tokens for new namespaces.
Scheduler: Watches newly created pods that have no node assigned, and selects a node for them to run on.
Api Server:The front-end for the Kubernetes control plane. It is designed to scale horizontally.Every other component contact with this to communicate.
Etcd Cluster: key/value backing store for cluster data,it stores state of the cluster (what nodes exist in the cluster, what pods should be running, which nodes they are running on, and a whole lot more) at any given point of time.
Components in Worker Nodes:
Kubelet:Agent that continuously watches API server. It makes sure that containers are running in a pod.
Kube-proxy: a proxy service that runs on each worker node to deal with individual host subnetting and expose services to the external world. It performs request forwarding to the correct pods/containers across the various isolated networks in a cluster. |
Various Ways of installing K8sminikube | single node cluster | kubeadm | multinode cluster(doesn't support kubenet, hence require CNI[container network interface] plugin eg. flannel. | GKE | multi node |
Important: The network must be deployed before any applications. Also, CoreDNS will not start up before a network is installed. kubeadm only supports Container Network Interface (CNI) based networks (and does not support kubenet). Output format in get-o wide | width wise details output | -o yaml | details output in yaml format | -o json | details output in json format |
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