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...)

.exercise[

• 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
  

]

---

Exporting the YAML for our application

• The following section assumes that DockerCoins is currently running

• If DockerCoins is not running, see next slide

.exercise[

• Create one YAML file for each resource that we need: .small[

  
    while read kind name; do
      kubectl get -o yaml $kind $name > dockercoins/templates/$name-$kind.yaml
    done <<EOF
    deployment worker
    deployment hasher
    daemonset rng
    deployment webui
    deployment redis
    service hasher
    service rng
    service webui
    service redis
    EOF
  

  ]

]

---

Obtaining DockerCoins YAML

• If DockerCoins is not running, we can also obtain the YAML from a public repository

.exercise[

• Clone the kubercoins repository:

  git clone https://github.com/jpetazzo/kubercoins
  

• Copy the YAML files to the templates/ directory:

  cp kubercoins/*.yaml dockercoins/templates/
  

]

---

Testing our helm chart

.exercise[

• Let's install our helm chart!

  helm install helmcoins dockercoins
  

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

]

--

• Since 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

• To avoid naming conflicts, we will deploy the application in another namespace

---

Switching to another namespace

• We need create a new namespace

  (Helm 2 creates namespaces automatically; Helm 3 doesn't anymore)

• We need to tell Helm which namespace to use

.exercise[

• 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

.exercise[

• 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

.exercise[

• 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

.exercise[

• 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

.exercise[

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

  helm delete helmcoins --namespace=helmcoins
  

]

???

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