DevOps Classroom Series – 18/Jul/2020 (Evening)

Challenges involved in K8s

• Resource Configuration Challenge:
  • Many typed of k8s resources:
    • Deployment
    • Pods
    • ReplicaSets
    • Service
    • Ingress
    • StorageClass
    • PersistentVolumeClaims
    • Secret
    • ConfigMap
    • And many more
  • Deploying an application on k8s is not simple, you need have understanding of all resource types
• Keeping the live and local states in sync:
  • K8s specifications will be created as yaml files stored in vcs like git
  • Whenever there are new changes we need to update git and pull those changes on server (local) and apply using kubectl (live).
  • But do you think this happens all the time?
  • In most of cases, we make local changes in the git apply it k8s (apply live state) and then commit changes to git (applying local states)
• Application life cycles are hard to manage
• Resource files are static
  • Even if the specifications are almost the same, since there is no parametrization, we need have multiple specs without reusability

Helm Comes to the rescue.

• To overcome challanges prompted a creation of simple but powerfull tool to deploy applications on k8s & that tool is helm
• Helm is often referred to as the Kubernetes Package Manager

Understanding package managers

• Package managers simplify process of installing, upgrading, reverting and removing system applications
• Applications are defined in units, these units are called as packages. Packages contain metadata around target software & its dependencies
• Lets take an example of you trying to install a software called as git
  • You will find the package name for git
  • Then you execute the command to install the package

  choco install git -y
  apt install git -y
  dnf install git --assumeyes # Fedora
  yum install git -y
  

  • Lets assume a new version of git is release

  choco upgrade git -y
  dnf upgrade git --assumeyes
  

  • if the new version is faulty, we can revert back to old version

  dnf downgrade git --assumeyes
  

  • If we want to remove software, we can execute

  dnf remove git --assumeyes
  

• Who ever is creating package will have specific implementation details
  • dnf operates on RPM package
  • apt operates on deb packages
  • choco operates on nuget package
• Once they create packages, they add metadata like version number etc and then they push the packages to some repository.
• User will fetch these packages from repository and install application software.

K8s package manager

• Helm works with charts. Charts are similar to packages.

• Helm chart can be thought as K8s package.

• Helm chart consists of

  • K8s resource files to deploy
  • some metadata
  • templates

• To learn helm lets create AKS and EKS cluster

EKS Cluster

• Installation Steps:

  • Creating AWS Ec2 instace,
  • Install AWS CLI
  • Install EKSCTL cli
  • Install kubectl
  • Use EKSCTL command to create cluster

• Follow the instructions to create cluster from here

• Also create AKS cluster if you have azure account credentials

Quick review of Helm

• Refer here for official docs
• Helm will have client component(helm-client) which generally runs along with kubectl and it also has server component (Tiller) which run in K8s cluster.
• Once we install helm, helm use kubectl config file to communicate with k8s cluster.
• Lets understand subcommands of helm
• Installing and configuring helm on the linux instance where kubectl is configured

curl -fsSL -o get_helm.sh https://raw.githubusercontent.com/helm/helm/master/scripts/get-helm-3
chmod 700 get_helm.sh
./get_helm.sh

helm help
helm version

• Lets add a repository to helm

helm repo add stable https://kubernetes-charts.storage.googleapis.com

• Lets install an example chart

helm repo update
helm repo add stable https://kubernetes-charts.storage.googleapis.com
helm search repo stable
helm version
helm repo update
helm search repo stable | grep mysql
helm install stable/mysql --generate-name

• clean up

Lets do one more helm chart installation for redis

• Lets use redis, lets use repositories from bitnami

helm repo add bitnami https://charts.bitnami.com/bitnami
helm install redis bitnami/redis --namespace=redis
kubectl get all -n redis

• If we get a new version of redis

helm upgrade redis bitnami/redis --namespace=redis

• If we want to rollback to previous version

helm rollback redis 1 --namespace=redis

• If we want to uninstall redis

helm uninstall redis --namespace=redis

How about creating charts?

• Lets create a helm chart

helm create learning

• When we create a helm chart a folder is created and in this folder there will subfolders and files

• Lets understand files/directory and their purpose

  • Chart.yaml: A file that consists of metatada about Helm chart. This is required
  • templates/: A directory that consists of k8s resources in YAML format.
  • templates/NOTES.txt: A file that can be generated to provided installation instructions during chart installation.
  • values.yaml: This file consists of charts default vaule.
  • .helmignore: ignore list (files/directoies) in the Helm chart package
  • charts/: A directory that consists of charts that this Helm chart is dependend on
  • Chart.lock: A file used to save previously applied dependecy version
  • README.md: This is documentation
  • LICENSE:
  • values.schema.json: A file contain the chars values schema in json format

• Lets look at the deployment.yaml in the templates folder

• Helm use Go templating Refer Here

• Go template control structures process begins with two opening curly braces and ends with two ending curly braces "{{ }}"

• "{{ }}" will pull the values from Values.yml or _helpers.tpl (*.tpl)

• Lets try to add dependencies to our chart

• Make the necessary changes and execute

• Now execute show values for dependency redis

helm show values chart/redis-10.7.11.tgz

• Lets install our chart

kubectl create namespace lnspace
helm install my-learning learning -n lnspace

• The helm chart created is shared over here