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Prepare for CSI snapshots with the snapshot validation webhook

Before we deploy snapshot-controller to actually manage the snapshots we take, we need the validation webhook to make sure it's done "right".

Snapshot Validation Webhook requirements

Ingredients

Already deployed:

Preparation

Snapshot Validation Webhook Namespace

We need a namespace to deploy our HelmRelease and associated YAMLs into. Per the flux design, I create this example yaml in my flux repo at /bootstrap/namespaces/namespace-snapshot-validation-webhook.yaml:

/bootstrap/namespaces/namespace-snapshot-validation-webhook.yaml
apiVersion: v1
kind: Namespace
metadata:
  name: snapshot-validation-webhook

Snapshot Validation Webhook HelmRepository

We're going to install the Snapshot Validation Webhook helm chart from the piraeus-charts repository, so I create the following in my flux repo (assuming it doesn't already exist):

/bootstrap/helmrepositories/helmrepository-piraeus-charts.yaml
apiVersion: source.toolkit.fluxcd.io/v1beta1
kind: HelmRepository
metadata:
  name: piraeus-charts
  namespace: flux-system
spec:
  interval: 15m
  url: https://piraeus.io/helm-charts/

Snapshot Validation Webhook Kustomization

Now that the "global" elements of this deployment (just the HelmRepository in this case) have been defined, we do some "flux-ception", and go one layer deeper, adding another Kustomization, telling flux to deploy any YAMLs found in the repo at /snapshot-validation-webhook/. I create this example Kustomization in my flux repo:

/bootstrap/kustomizations/kustomization-snapshot-validation-webhook.yaml
apiVersion: kustomize.toolkit.fluxcd.io/v1beta2
kind: Kustomization
metadata:
  name: snapshot-validation-webhook
  namespace: flux-system
spec:
  interval: 30m
  path: ./snapshot-validation-webhook
  prune: true # remove any elements later removed from the above path
  timeout: 10m # if not set, this defaults to interval duration, which is 1h
  sourceRef:
    kind: GitRepository
    name: flux-system
  healthChecks:
    - apiVersion: helm.toolkit.fluxcd.io/v2beta1
      kind: HelmRelease
      name: snapshot-validation-webhook
      namespace: snapshot-validation-webhook

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Snapshot Validation Webhook HelmRelease

Lastly, having set the scene above, we define the HelmRelease which will actually deploy snapshot-validation-webhook into the cluster. We start with a basic HelmRelease YAML, like this example:

/snapshot-validation-webhook/helmrelease-snapshot-validation-webhook.yaml
apiVersion: helm.toolkit.fluxcd.io/v2beta1
kind: HelmRelease
metadata:
  name: snapshot-validation-webhook
  namespace: snapshot-validation-webhook
spec:
  chart:
    spec:
      chart: snapshot-validation-webhook
      version: 1.8.x # auto-update to semver bugfixes only (1)
      sourceRef:
        kind: HelmRepository
        name: piraeus-charts
        namespace: flux-system
  interval: 15m
  timeout: 5m
  releaseName: snapshot-validation-webhook
  values: # paste contents of upstream values.yaml below, indented 4 spaces (2)
  1. I like to set this to the semver minor version of the Snapshot Validation Webhook current helm chart, so that I'll inherit bug fixes but not any new features (since I'll need to manually update my values to accommodate new releases anyway)
  2. Paste the full contents of the upstream values.yaml here, indented 4 spaces under the values: key

If we deploy this helmrelease as-is, we'll inherit every default from the upstream Snapshot Validation Webhook helm chart. That's probably hardly ever what we want to do, so my preference is to take the entire contents of the Snapshot Validation Webhook helm chart's values.yaml, and to paste these (indented), under the values key. This means that I can then make my own changes in the context of the entire values.yaml, rather than cherry-picking just the items I want to change, to make future chart upgrades simpler.

Why not put values in a separate ConfigMap?

Didn't you previously advise to put helm chart values into a separate ConfigMap?

Yes, I did. And in practice, I've changed my mind.

Why? Because having the helm values directly in the HelmRelease offers the following advantages:

  1. If you use the YAML extension in VSCode, you'll see a full path to the YAML elements, which can make grokking complex charts easier.
  2. When flux detects a change to a value in a HelmRelease, this forces an immediate reconciliation of the HelmRelease, as opposed to the ConfigMap solution, which requires waiting on the next scheduled reconciliation.
  3. Renovate can parse HelmRelease YAMLs and create PRs when they contain docker image references which can be updated.
  4. In practice, adapting a HelmRelease to match upstream chart changes is no different to adapting a ConfigMap, and so there's no real benefit to splitting the chart values into a separate ConfigMap, IMO.

Then work your way through the values you pasted, and change any which are specific to your configuration.

Install Snapshot Validation Webhook!

Commit the changes to your flux repository, and either wait for the reconciliation interval, or force a reconcilliation using flux reconcile source git flux-system. You should see the kustomization appear...

~ ❯ flux get kustomizations snapshot-validation-webhook
NAME        READY   MESSAGE                         REVISION        SUSPENDED
snapshot-validation-webhook True    Applied revision: main/70da637  main/70da637    False
~ ❯

The helmrelease should be reconciled...

~ ❯ flux get helmreleases -n snapshot-validation-webhook snapshot-validation-webhook
NAME        READY   MESSAGE                             REVISION    SUSPENDED
snapshot-validation-webhook True    Release reconciliation succeeded    v1.8.x      False
~ ❯

And you should have happy pods in the snapshot-validation-webhook namespace:

~ ❯ k get pods -n snapshot-validation-webhook -l app.kubernetes.io/name=snapshot-validation-webhook
NAME                                  READY   STATUS    RESTARTS   AGE
snapshot-validation-webhook-7c94b7446d-nwsss   1/1     Running   0          5m14s
~ ❯

Summary

What have we achieved? We now have the snapshot validation admission webhook running in the cluster, ready to support snapshot-controller!

Summary

Created:

  • snapshot-validation-webhook running and ready to validate!

Next:

Chef's notes 📓

///Footnotes Go Here///

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