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Kubernetes.md

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##Kubernetes Introduction

Kubernetes is an open-source container orchestration platform that automates the deployment, management, scaling, and networking of containers.

It was developed by Google using the Go Programming Language, and this amazing technology has been open-source since 2014.

minikube commands

minikube start
minikube dashboard
minikube stop

Accessing minikube

kubectl config view
kubectl cluster-info
kubectl proxy
# This opens a proxy to kubernetes REST API
curl http://localhost:8081/
# Get the token
TOKEN=$(kubectl describe secret $(kubectl get secrets | grep default | cut -f1 -d ' ') | grep -E '^token' | cut -f2 -d':' | tr -d '\t')
# Get the API server endpoint
APISERVER=$(kubectl config view | grep https | cut -f 2- -d ":" | tr -d " ")
# Access the API Server using the endpoint and credentials
curl $APISERVER --header "Authorization: Bearer $TOKEN" --insecure

Pods

A Pod is the smallest and simplest Kubernetes object. It is the unit of deployment in Kubernetes, which represents a single instance of the application. A Pod is a logical collection of one or more containers, which:

  • Are scheduled together on the same host
  • Share the same network namespace
  • Mount the same external storage (Volumes).

pod

Pods are ephemeral in nature, and they do not have the capability to self-heal by themselves. That is why we use them with controllers, which can handle a Pod's replication, fault tolerance, self-heal, etc. Examples of controllers are Deployments, ReplicaSets, ReplicationControllers, etc. We attach the Pod's specification to other objects using Pod Templates, as we have seen in the previous section.

Using staged repositories from Kubernetes code

Kubernetes code uses the repositories in this directory via symlinks in the vendor/k8s.io directory into this staging area. For example, when Kubernetes code imports a package from the k8s.io/client-go repository, that import is resolved to staging/src/k8s.io/client-go relative to the project root:

// pkg/example/some_code.go
package example

import (
  "k8s.io/client-go/dynamic" // resolves to staging/src/k8s.io/client-go/dynamic
)

Once the change-over to external repositories is complete, these repositories will actually be vendored from k8s.io/<package-name>.

Creating a new repository in staging

Adding the staging repository in kubernetes/kubernetes:

  1. Send an email to the SIG Architecture mailing list and the mailing list of the SIG which would own the repo requesting approval for creating the staging repository.

  2. Once approval has been granted, create the new staging repository.

  3. Add a symlink to the staging repo in vendor/k8s.io.

  4. Update import-restrictions.yaml to add the list of other staging repos that this new repo can import.

  5. Add all mandatory template files to the staging repo as mentioned in https:/kubernetes/kubernetes-template-project.

  6. Make sure that the .github/PULL_REQUEST_TEMPLATE.md and CONTRIBUTING.md files mention that PRs are not directly accepted to the repo.

  7. Ensure that docs.go file is added. Refer to #kubernetes/kubernetes#91354 for reference.

If using ManagedAuth, replace the template variables in tasks/add-auth-client-bare-pod.yaml. Apply this file, check it for completion, and delete it. Repeat for each client ID.

  1. Expose your application to the world by replacing the template variables in ingress/nginx-https.yaml and applying it.

Files to check in to version control

Obfuscate any secret values - those in config/secrets.yaml and tasks/add-auth-client-bare-pod.yaml and check in all files in k8s.

Updating the Application

For application updates that do not require database schema changes, build the Docker image and push it to the registry with gcloud. If you are tagging images correctly, just set the image of your deployment:

kubectl set image deployment/api-deployment <app-name>=gcr.io/<project-id>/<app-name>:<tag> -n <app-name>

If you are reusing the latest tag, delete all pods in the api-deployment.

kubectl delete pod api-deployment-xxxxxxx-xxxxx -n <app-name>

The pods will automatically be recreated and will pull the most recent image.

If a database update is required, make sure to run aqueduct db generate before building and pushing the Docker image. Then follow the instructions in step 5 before deleting pods.

*Note: This scheme is useful for development. When deploying to production, a unique tag should be used for each image and that image name should be added to the api-deployment-and-service.yaml. Instead of deleting pods, re-apply this configuration file:

kubectl apply -f k8s/api-deployment-and-service.yaml