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218 lines
4.3 KiB
Markdown
218 lines
4.3 KiB
Markdown
# Managing stacks with Helm
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- We created our first resources with `kubectl run`, `kubectl expose` ...
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- We have also created resources by loading YAML files with `kubectl apply -f`
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- For larger stacks, managing thousands of lines of YAML is unreasonable
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- These YAML bundles need to be customized with variable parameters
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(E.g.: number of replicas, image version to use ...)
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- It would be nice to have an organized, versioned collection of bundles
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- It would be nice to be able to upgrade/rollback these bundles carefully
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- [Helm](https://helm.sh/) is an open source project offering all these things!
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---
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## Helm concepts
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- `helm` is a CLI tool
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- `tiller` is its companion server-side component
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- A "chart" is an archive containing templatized YAML bundles
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- Charts are versioned
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- Charts can be stored on private or public repositories
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---
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## Installing Helm
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- We need to install the `helm` CLI; then use it to deploy `tiller`
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.exercise[
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- Install the `helm` CLI:
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```bash
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curl https://raw.githubusercontent.com/kubernetes/helm/master/scripts/get | bash
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```
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- Deploy `tiller`:
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```bash
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helm init
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```
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- Add the `helm` completion:
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```bash
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. <(helm completion $(basename $SHELL))
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```
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]
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---
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## Fix account permissions
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- Helm permission model requires us to tweak permissions
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- In a more realistic deployment, you might create per-user or per-team
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service accounts, roles, and role bindings
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.exercise[
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- Grant `cluster-admin` role to `kube-system:default` service account:
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```bash
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kubectl create clusterrolebinding add-on-cluster-admin \
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--clusterrole=cluster-admin --serviceaccount=kube-system:default
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```
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]
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(Defining the exact roles and permissions on your cluster requires
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a deeper knowledge of Kubernetes' RBAC model. The command above is
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fine for personal and development clusters.)
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---
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## View available charts
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- A public repo is pre-configured when installing Helm
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- We can view available charts with `helm search` (and an optional keyword)
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.exercise[
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- View all available charts:
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```bash
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helm search
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```
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- View charts related to `prometheus`:
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```bash
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helm search prometheus
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```
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]
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---
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## Install a chart
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- Most charts use `LoadBalancer` service types by default
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- Most charts require persistent volumes to store data
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- We need to relax these requirements a bit
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.exercise[
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- Install the Prometheus metrics collector on our cluster:
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```bash
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helm install stable/prometheus \
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--set server.service.type=NodePort \
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--set server.persistentVolume.enabled=false
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```
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]
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Where do these `--set` options come from?
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---
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## Inspecting a chart
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- `helm inspect` shows details about a chart (including available options)
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.exercise[
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- See the metadata and all available options for `stable/prometheus`:
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```bash
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helm inspect stable/prometheus
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```
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]
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The chart's metadata includes an URL to the project's home page.
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(Sometimes it conveniently points to the documentation for the chart.)
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---
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## Creating a chart
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- We are going to show a way to create a *very simplified* chart
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- In a real chart, *lots of things* would be templatized
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(Resource names, service types, number of replicas...)
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.exercise[
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- Create a sample chart:
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```bash
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helm create dockercoins
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```
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- Move away the sample templates and create an empty template directory:
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```bash
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mv dockercoins/templates dockercoins/default-templates
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mkdir dockercoins/templates
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```
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]
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---
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## Exporting the YAML for our application
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- The following section assumes that DockerCoins is currently running
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.exercise[
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- Create one YAML file for each resource that we need:
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.small[
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```bash
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while read kind name; do
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kubectl get -o yaml --export $kind $name > dockercoins/templates/$name-$kind.yaml
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done <<EOF
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deployment worker
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deployment hasher
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daemonset rng
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deployment webui
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deployment redis
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service hasher
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service rng
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service webui
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service redis
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EOF
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```
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]
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]
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---
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## Testing our helm chart
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.exercise[
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- Let's install our helm chart! (`dockercoins` is the path to the chart)
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```bash
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helm install dockercoins
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```
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]
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--
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- Since the application is already deployed, this will fail:<br>
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`Error: release loitering-otter failed: services "hasher" already exists`
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- To avoid naming conflicts, we will deploy the application in another *namespace*
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