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kubernetes-setup.md

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Setup Kubernetes

Installing and setting up a Kubernetes on a local machine.

Install kubectl

Install the Kubernetes command-line tool called kubectl to deploy and manage applications on Kubernetes.

For macOS: brew install kubernetes-cli

Configure kubectl

vim ~/.kube/config

apiVersion: v1
clusters:
- cluster:
    certificate-authority: /Users/damber/k8s/prod_ca.pem
    server: https://203.119.108.20:6443
  name: prod

...

  user:
    client-certificate: /Users/damber/k8s/cert.pem
    client-key: /Users/damber/k8s/key.pem

We need to create certificate-authority, client-certificate and client-key keys as mentioned in config file.

  • Create folder k8s in home directory

  • Create certificate authority touch k8s\prod_ca.pem and add digital certificate to certify the ownership of a public key.

  • Create client certificate using your certificate to make authenticated request to a remote server.

    openssl pkcs12 -in <YOUR_CERTIFICATE>.p12 -out cert.pem -nodes -nokeys

  • Create client key

    openssl pkcs12 -in <YOUR_CERTIFICATE>.p12 -out key.pem -nodes -nocerts

Verify kubectl

kubectl version

kubectl cluster-info

Terminology

1. Pods

A Pod is a logical wrapper around running containers which hold an application. For example, a Pod may have mysql database container, microservices container, and wordpress container running together as an application.

Pods

2. Nodes

Node is a worker machine in Kubernetes, managed by the Master.

  • Node can have multiple pods
  • Node can have multiple clusters
  • Each pod is tied to the Node where it is scheduled by the Master and in case of a Node failure, the pods are scheduled on other available Nodes in the cluster.

Node Components:

  • Kubelet Service: It enable communication between Kubernetes master and the node to receive commands and work. It also manages network rules and port etc.
  • Docker: Pull the container image from a registry, unpack them, and run the application.
  • Kube Proxy Service: It runs on each node making services available to the external host. Basically, it manages networking part for nodes.

Node

3. Replication Controllers

Replication controllers ensure that a specific number of pod replicas are running at any one time. It manages cluster (group of pods), scale up cluster (by creating extra pod copies), scale down cluster (by removing a few copies). It can monitor each pod and if one is unresponsive or misbehave, it can kill that one and bring on a suitable replacement.

Replication Controller

4. Services

Services defines a logical set of Pods and a policy by which to access them over the network. For example, a service preserves IP addresses and ports so that DNS names can map to the same thing.

Services

5. Volume

A place to store data that lives longer than a pod for an application.

Volumes

6. Namespaces

A way of encapsulating pods, replication controllers, services and volumes into big group called namespace. It isolate its contents from everybody's stuff.

Namespaces

7. Deployment

To deploy your containerized applications you need to create a Kubernetes Deployment configuration. It instructs Kubernetes how to create/update instances of your application, generate pods and connect to other services. When we create a deployment on kubernetes, it creates pods with containers inside them.

8. Secret

A secret hold sensitive information such as passowords, OAuth token, and ssh keys. It allow for more control, secure and flexible storage of sensitive information.

9. PVC

PersistentVolume (PV) provides an API for users and administrators that abstracts details of how storage is provided from how it is consumed.

PersistantVolumeClaim (PVC) is a request for storage by a user. It is similar to a pod. Pods consume node resources and PVCs consume PV resources.

10. Quota

It's useful to know about the aggregate resource consumption per namespace as you will at times check if the namespace has enough computational resources for your pod.

  • Get quota name kubectl get quota
  • Describe kubectl describe quota <quota-name>
Name:            compute-resources
Namespace:       webops-uat
Resource         Used    Hard
--------         ----    ----
limits.cpu       1850m   4
limits.memory    3584Mi  8Gi
pods             4       8
requests.cpu     1200m   2
requests.memory  2560Mi  4Gi