feat: add version-aware helm chart upgrade callbacks

Some helm chart upgrades require side-effects that a plain `helm upgrade` cannot perform, such as deleting deployments whose immutable selectors changed. Charts may now register pre and post upgrade hooks against a target version; applicable hooks fire in ascending semver order, each bracketed around an upgrade to its version, with a final upgrade to the chart's configured version when needed. The new `keda-add-ons-http` 0.12.2 hook deletes the chart-managed deployments before the upgrade so the new selectors take effect cleanly.

plugins/scheduler-k3s/chart_hooks.go

@@ -0,0 +1,104 @@
+package scheduler_k3s
+
+import (
+	"context"
+	"fmt"
+	"sort"
+
+	"github.com/Masterminds/semver/v3"
+)
+
+// ChartHookFunc is the signature for a function that runs around a helm chart
+// upgrade. It receives the active Kubernetes client, the chart definition, and
+// the helm release that was installed before the upgrade started.
+type ChartHookFunc func(ctx context.Context, clientset KubernetesClient, chart HelmChart, installedRevision Release) error
+
+// ChartHook attaches version-specific behaviour to a helm chart upgrade. A
+// hook fires when the currently installed release version is below
+// TargetVersion and the chart's configured target version is at or above
+// TargetVersion. PreUpgrade runs before the chart is upgraded to
+// TargetVersion; PostUpgrade runs after that intermediate upgrade succeeds.
+type ChartHook struct {
+	TargetVersion string
+	PreUpgrade    ChartHookFunc
+	PostUpgrade   ChartHookFunc
+}
+
+// ChartHooks is keyed by HelmChart.ReleaseName. selectChartHooks resorts
+// entries by semver, so authoring order is informative rather than load-bearing.
+var ChartHooks = map[string][]ChartHook{
+	"keda-add-ons-http": {
+		{
+			TargetVersion: "0.12.2",
+			PreUpgrade:    deleteKedaAddOnsHttpDeployments,
+		},
+	},
+}
+
+// selectChartHooks returns the hooks for releaseName whose TargetVersion is
+// strictly greater than installedVersion and less than or equal to
+// targetVersion, sorted ascending by TargetVersion. An empty installedVersion
+// signals a fresh install and yields no hooks.
+func selectChartHooks(releaseName, installedVersion, targetVersion string) ([]ChartHook, error) {
+	if installedVersion == "" {
+		return nil, nil
+	}
+
+	hooks, ok := ChartHooks[releaseName]
+	if !ok || len(hooks) == 0 {
+		return nil, nil
+	}
+
+	installed, err := semver.NewVersion(installedVersion)
+	if err != nil {
+		return nil, fmt.Errorf("Invalid installed version %q for chart %s: %w", installedVersion, releaseName, err)
+	}
+
+	target, err := semver.NewVersion(targetVersion)
+	if err != nil {
+		return nil, fmt.Errorf("Invalid target version %q for chart %s: %w", targetVersion, releaseName, err)
+	}
+
+	type indexedHook struct {
+		version *semver.Version
+		hook    ChartHook
+	}
+
+	selected := []indexedHook{}
+	for _, hook := range hooks {
+		hookVersion, err := semver.NewVersion(hook.TargetVersion)
+		if err != nil {
+			return nil, fmt.Errorf("Invalid hook TargetVersion %q for chart %s: %w", hook.TargetVersion, releaseName, err)
+		}
+
+		if hookVersion.Compare(installed) <= 0 {
+			continue
+		}
+		if hookVersion.Compare(target) > 0 {
+			continue
+		}
+
+		selected = append(selected, indexedHook{version: hookVersion, hook: hook})
+	}
+
+	sort.Slice(selected, func(i, j int) bool {
+		return selected[i].version.LessThan(selected[j].version)
+	})
+
+	out := make([]ChartHook, 0, len(selected))
+	for _, entry := range selected {
+		out = append(out, entry.hook)
+	}
+	return out, nil
+}
+
+// deleteKedaAddOnsHttpDeployments removes the deployments managed by the
+// keda-add-ons-http helm release so the chart can recreate them with the
+// updated selectors introduced in 0.12.x. Selectors on Deployments are
+// immutable, so a straight helm upgrade fails without this step.
+func deleteKedaAddOnsHttpDeployments(ctx context.Context, clientset KubernetesClient, chart HelmChart, installedRevision Release) error {
+	return clientset.DeleteDeployment(ctx, DeleteDeploymentInput{
+		Namespace:     chart.Namespace,
+		LabelSelector: "app.kubernetes.io/instance=keda-add-ons-http",
+	})
+}