container.training/slides/kube/helm.md

Managing stacks with Helm

• We created our first resources with kubectl run, kubectl expose ...

• We have also created resources by loading YAML files with kubectl apply -f

• For larger stacks, managing thousands of lines of YAML is unreasonable

• These YAML bundles need to be customized with variable parameters

  (E.g.: number of replicas, image version to use ...)

• It would be nice to have an organized, versioned collection of bundles

• It would be nice to be able to upgrade/rollback these bundles carefully

• Helm is an open source project offering all these things!

---

Helm concepts

• helm is a CLI tool

• tiller is its companion server-side component

• A "chart" is an archive containing templatized YAML bundles

• Charts are versioned

• Charts can be stored on private or public repositories

---

Installing Helm

• We need to install the helm CLI; then use it to deploy tiller

.exercise[

• Install the helm CLI:

  curl https://raw.githubusercontent.com/kubernetes/helm/master/scripts/get | bash
  

• Deploy tiller:

  helm init
  

]

---

Fix account permissions

• Helm permission model requires us to tweak permissions

• In a more realistic deployment, you might create per-user or per-team service accounts, roles, and role bindings

.exercise[

• Grant cluster-admin role to kube-system:default service account:

  kubectl create clusterrolebinding add-on-cluster-admin \
      --clusterrole=cluster-admin --serviceaccount=kube-system:default
  

]

(Defining the exact roles and permissions on your cluster requires a deeper knowledge of Kubernetes' RBAC model. The command above is fine for personal and development clusters.)

---

View available charts

• A public repo is pre-configured when installing Helm

• We can view available charts with helm search (and an optional keyword)

.exercise[

• View all available charts:

  helm search
  

• View charts related to gitlab:

  helm search gitlab
  

]

---

Install a chart

• Most charts use LoadBalancer service types by default

• Most charts require persistent volumes to store data

• We need to relax these requirements a bit

.exercise[

• Install the Prometheus metrics collector on our cluster:

  helm install stable/prometheus \
         --set server.service.type=NodePort \
         --set server.persistentVolume.enabled=false
  

]

Where do these --set options come from?

---

Inspecting a chart

• helm inspect shows details about a chart (including available options)

.exercise[

• See the metadata and all available options for stable/prometheus:

  helm inspect stable/prometheus
  

]

The chart's metadata includes an URL to the project's home page.

(Sometimes it conveniently points to the documentation for the chart.)

---

Creating a 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:

  mv dockercoins/templates dockercoins/default-templates
  

]

---

Exporting the YAML for our application

• The following section assumes that DockerCoins is currently running

.exercise[

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

  
    while read kind name; do
      kubectl get -o yaml --export $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
  

  ]

]

---

Testing our chart

• We can now install our chart with helm install dockercoins

  (In that case, dockercoins is the path to the chart)

• However, since the application is already deployed, this will fail

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