container.training/slides/k8s/helm-create-basic-chart.md

Creating a basic chart

• We are going to show a way to create a very simplified chart

• In a real chart, lots of things would be templatized

  (Resource names, service types, number of replicas...)

.lab[

• Create a sample chart:

  helm create dockercoins
  

• Move away the sample templates and create an empty template directory:

  mv dockercoins/templates dockercoins/default-templates
  mkdir dockercoins/templates
  

]

---

Adding the manifests of our app

• There is a convenient dockercoins.yml in the repo

.lab[

• Copy the YAML file to the templates subdirectory in the chart:

  cp ~/container.training/k8s/dockercoins.yaml dockercoins/templates
  

]

• Note: it is probably easier to have multiple YAML files

  (rather than a single, big file with all the manifests)

• But that works too!

---

Testing our Helm chart

• Our Helm chart is now ready

  (as surprising as it might seem!)

.lab[

• Let's try to install the chart:

  helm install helmcoins dockercoins
  

  (helmcoins is the name of the release; dockercoins is the local path of the chart)

]

--

• If the application is already deployed, this will fail:

Error: rendered manifests contain a resource that already exists.
Unable to continue with install: existing resource conflict:
kind: Service, namespace: default, name: hasher

---

Switching to another namespace

• If there is already a copy of dockercoins in the current namespace:

  • we can switch with kubens or kubectl config set-context

  • we can also tell Helm to use a different namespace

.lab[

• Create a new namespace:

  kubectl create namespace helmcoins
  

• Deploy our chart in that namespace:

  helm install helmcoins dockercoins --namespace=helmcoins
  

]

---

Helm releases are namespaced

• Let's try to see the release that we just deployed

.lab[

• List Helm releases:

  helm list
  

]

Our release doesn't show up!

We have to specify its namespace (or switch to that namespace).

---

Specifying the namespace

• Try again, with the correct namespace

.lab[

• List Helm releases in helmcoins:

  helm list --namespace=helmcoins
  

]

---

Checking our new copy of DockerCoins

• We can check the worker logs, or the web UI

.lab[

• Retrieve the NodePort number of the web UI:

  kubectl get service webui --namespace=helmcoins
  

• Open it in a web browser

• Look at the worker logs:

  kubectl logs deploy/worker --tail=10 --follow --namespace=helmcoins
  

]

Note: it might take a minute or two for the worker to start.

---

Discussion, shortcomings

• Helm (and Kubernetes) best practices recommend to add a number of annotations

  (e.g. app.kubernetes.io/name, helm.sh/chart, app.kubernetes.io/instance ...)

• Our basic chart doesn't have any of these

• Our basic chart doesn't use any template tag

• Does it make sense to use Helm in that case?

• Yes, because Helm will:

  • track the resources created by the chart

  • save successive revisions, allowing us to rollback

Helm docs and Kubernetes docs have details about recommended annotations and labels.

---

Cleaning up

• Let's remove that chart before moving on

.lab[

• Delete the release (don't forget to specify the namespace):

  helm delete helmcoins --namespace=helmcoins
  

]

---

Tips when writing charts

• It is not necessary to helm install/upgrade to test a chart

• If we just want to look at the generated YAML, use helm template:

  helm template ./my-chart
  helm template release-name ./my-chart
  

• Of course, we can use --set and --values too

• Note that this won't fully validate the YAML!

  (e.g. if there is apiVersion: klingon it won't complain)

• This can be used when trying things out

---

Exploring the templating system

Try to put something like this in a file in the templates directory:

hello: {{ .Values.service.port }}
comment: {{/* something completely.invalid !!!  */}}
type: {{ .Values.service | typeOf | printf }}
### print complex value
{{ .Values.service | toYaml }}
### indent it
indented:
{{ .Values.service | toYaml | indent 2 }}

Then run helm template.

The result is not a valid YAML manifest, but this is a great debugging tool!

???

:EN:- Writing a basic Helm chart for the whole app :FR:- Écriture d'un chart Helm simplifié