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KodeCloud CKAD Helm Charts

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What are Helm Charts

  • Helm is also known as a package manager for k8s.
  • We use a single command to install our application even if it needs hundreds of objects.
  • We can customise the settings we want for our app by specifying desired values at install time (values.yaml).
    • Instead of editing multiple values in multiple yaml files we have a single location where we can declare every custom setting.
Helm lets us treat our app as an app rather than a collection of objects.

This means that we don't have to micro manage the k8s objects.

  • Running helm in verbose mode: helm --debug
  • Helm has a CLI client installed on our local machine that helps us perform helm specific actions against our k8s cluster.

Difference between Helm 2 & Helm 3

  • There were some significant changes between helm 2 and helm 3.
  • Helm 1 (2016) -> Helm 2 (2016) -> Helm 3 (2019)
  • When Helm 2 was around k8s lacked features like RBAC, CRDs

    • To allow helm to do its magic an extra component called Tiller had to be installed in the k8s cluster.
    • Helm CLI communicated with Tiller and Tiller then communicated with the cluster.
    • Tiller also operated in God mode which posed security concerns.
    • attachments/Pasted image 20221003233736.jpg
  • With the addition of RBAC and CRDs Tiller was removed from Helm 3.

  • Helm 3 uses 3 way strategic merge:

    • This means Helm 3 also takes into consideration the live state when performing rollbacks.
      • attachments/Pasted image 20221003234852.jpg
    • Helm 2 only considered the previous chart and the current chart when performing rollbacks.

Helm components

  • Charts are a collection of files.
  • They contain all the instructions helm needs to know to be able to create the collection of objects.

  • When a chart is applied to our cluster a release is created.

    • A release is a single installation of an application using a helm chart.
    • Within each release we can have multiple revisions.
  • Each revision is like a snapshot of the application.

    • Every time a change to the application is made like upgrade of an image or change of replicas a new revision is created.
  • We can find the helm charts in a public repository. We can use them to deploy applications on our cluster.
  • To keep track of what it did on our cluster it saves it as metadata.

    • Helm saves this metadata directly in our k8s cluster as k8s secrets.
  • Templating in charts

    • values.yaml is the file where configurable values are stored and most of the times it is the only file that we will need to modify to customise the deployment of the application.
    • attachments/Pasted image 20221004000946.jpg
  • Charts are more complicated for complex applications like a wordpress application.

  • helm install <release-name> <chart-name>

    • We have release names with charts because we can have multiple releases with the same chart.
    • These 2 separate releases can be tracked separately even though they are from the same chart.
    • attachments/Pasted image 20221004001326.jpg
  • Upgrading the application: helm upgrade <release-name>

  • Roll back to the previous revision using: helm rollback <release-name>
  • Uninstalling the app: helm uninstall <release-name>

    • It keeps track of all the objects used by each app so it knows what to remove.
    • We don't need to remember each object that belongs to our app anymore.
  • Apart from values.yaml file every chart has a chart.yaml file.

    • It contains information about the chart itself.
    • apiVersion for helm 2 is v1 and for helm 3 is v2. If a chart does not have this value set then it means that it was built for helm 2.
    • There are 2 types of chart: application and library.
    • In the dependencies section we can add other charts as dependencies.
    • attachments/Pasted image 20221004101549.jpg
  • Helm chart structure:

    • attachments/Pasted image 20221004101630.jpg
  • We can find help on any command or subcommand of helm using --help

    • helm --help: to get a list of commands that we can use
    • helm <command> --help
    • helm <command> <sub-command> --help
  • We can search for charts in the artifact hub using the helm cli:

    • helm search hub <application-name>
  • If you have added a repo using helm repo <name> <url> then you can search in it using

    • helm search repo <application-name>
  • We can list all existing releases using helm list

  • List all the repositories present: helm repo list
  • Refreshing the repos: helm repo update

    • It is just like sudo apt update
    • This is needed since the information helm has about the repositories is stored locally and it gets updated over time.
  • We can install a specific version of helm chart using:

    • helm install <release-name> <chart-name> --version 3.3
    • This is the chart version and NOT the application version.

Customising chart parameters

  • values.yaml file
    • attachments/Pasted image 20221005225341.jpg
  • Using set option to customise the value
    • helm install --set wordpressBlogName-"Helm Tutorials" my-release bitnami/wordpress
    • This can be used multiple times to pass multiple parameters to the command line.
    • These override the values set in values.yaml file.
    • attachments/Pasted image 20221005225813.jpg
  • If there are too many of these values we can move them to our own custom values yaml file.
    • This will now override the values in the default value.yaml file.
    • helm install --values custom-values.yaml my-release bitnami/wordpress
What if we want to change the values in values.yaml without using a custom values file or --set option

We will break it into 2 commands. - We will first pull the chart using helm pull bitnami/wordpress in an archive or compressed form. - We can uncompress it using helm while pulling using the helm pull --untar bitnami/wordpress - We then run the charts helm install <release-name> <extracted-folder-name> attachments/Pasted image 20221005234808.jpg

Lifecycle management

  • More details about a particular release:
    • helm history <release-name>
  • Going back to a previous release
    • helm rollback <release-name> <revision-number>
    • Here revision number is the number we want to revert back to.
Suppose we do a rollback from v2 to v1, technically helm does not go back to v1, instead it creates a new revision (v3) with a similar configuration to v1.
  • Although rollbacks are very similar to backup restore feature, it does not cover file or directory data that may be created by our application.
    • So for things that use persistent volumes, rollback won't restore the data.
    • This is done using chart hooks

Last updated: 2022-10-06