feat: wire render cache into prebuilds reconciler

Callum Styan · claude · Callum Styan · commit 72d711dde237 · 2025-12-09T21:47:55.000Z
This commit integrates the render cache into the prebuilds reconciliation flow, enabling cache sharing across all prebuild operations. Changes: 1. StoreReconciler: - Add renderCache field (*dynamicparameters.RenderCache) - Initialize cache in NewStoreReconciler() - Pass cache to builder in provision() method 2. wsbuilder.Builder: - Add renderCache field - Add RenderCache(cache) builder method - Pass cache to dynamicparameters.Prepare() when available How it works: - Single RenderCache instance shared across all prebuilds - Each workspace build passes the cache through the builder chain - Cache keyed by (templateVersionID, ownerID, parameterHash) - All prebuilds use PrebuildsSystemUserID, maximizing cache hits Expected behavior for a preset with 5 instances: - First instance: cache miss → full render → cache stored - Instances 2-5: cache hit → instant return - Result: ~80% reduction in render operations per cycle This addresses the resource cost identified in profiling where the prebuilds path consumed 25% CPU and 50% memory allocations, primarily from repeated Terraform file parsing. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
diff --git a/coderd/wsbuilder/wsbuilder.go b/coderd/wsbuilder/wsbuilder.go
@@ -88,6 +88,9 @@ type Builder struct {
 	parameterRender                      dynamicparameters.Renderer
 	workspaceTags                        *map[string]string
 
+	// renderCache caches template rendering results
+	renderCache *dynamicparameters.RenderCache
+
 	prebuiltWorkspaceBuildStage  sdkproto.PrebuiltWorkspaceBuildStage
 	verifyNoLegacyParametersOnce bool
 }
@@ -253,6 +256,14 @@ func (b Builder) TemplateVersionPresetID(id uuid.UUID) Builder {
 	return b
 }
 
+// RenderCache sets the render cache to use for template rendering.
+// This allows multiple workspace builds to share cached render results.
+func (b Builder) RenderCache(cache *dynamicparameters.RenderCache) Builder {
+	// nolint: revive
+	b.renderCache = cache
+	return b
+}
+
 type BuildError struct {
 	// Status is a suitable HTTP status code
 	Status  int
@@ -686,6 +697,22 @@ func (b *Builder) getDynamicParameterRenderer() (dynamicparameters.Renderer, err
 		return nil, xerrors.Errorf("get template version variables: %w", err)
 	}
 
+	// Pass render cache if available
+	if b.renderCache != nil {
+		renderer, err := dynamicparameters.Prepare(b.ctx, b.store, b.fileCache, tv.ID,
+			dynamicparameters.WithTemplateVersion(*tv),
+			dynamicparameters.WithProvisionerJob(*job),
+			dynamicparameters.WithTerraformValues(*tfVals),
+			dynamicparameters.WithTemplateVariableValues(variableValues),
+			dynamicparameters.WithRenderCache(b.renderCache),
+		)
+		if err != nil {
+			return nil, xerrors.Errorf("get template version renderer: %w", err)
+		}
+		b.parameterRender = renderer
+		return renderer, nil
+	}
+
 	renderer, err := dynamicparameters.Prepare(b.ctx, b.store, b.fileCache, tv.ID,
 		dynamicparameters.WithTemplateVersion(*tv),
 		dynamicparameters.WithProvisionerJob(*job),
diff --git a/enterprise/coderd/prebuilds/reconcile.go b/enterprise/coderd/prebuilds/reconcile.go
@@ -26,6 +26,7 @@ import (
 	"github.com/coder/coder/v2/coderd/database/dbauthz"
 	"github.com/coder/coder/v2/coderd/database/provisionerjobs"
 	"github.com/coder/coder/v2/coderd/database/pubsub"
+	"github.com/coder/coder/v2/coderd/dynamicparameters"
 	"github.com/coder/coder/v2/coderd/files"
 	"github.com/coder/coder/v2/coderd/notifications"
 	"github.com/coder/coder/v2/coderd/prebuilds"
@@ -58,6 +59,9 @@ type StoreReconciler struct {
 	metrics *MetricsCollector
 	// Operational metrics
 	reconciliationDuration prometheus.Histogram
+
+	// renderCache caches template rendering results to avoid expensive re-parsing
+	renderCache *dynamicparameters.RenderCache
 }
 
 var _ prebuilds.ReconciliationOrchestrator = &StoreReconciler{}
@@ -102,6 +106,7 @@ func NewStoreReconciler(store database.Store,
 		buildUsageChecker: buildUsageChecker,
 		done:              make(chan struct{}, 1),
 		provisionNotifyCh: make(chan database.ProvisionerJob, 10),
+		renderCache:       dynamicparameters.NewRenderCache(),
 	}
 
 	if registerer != nil {
@@ -900,7 +905,8 @@ func (c *StoreReconciler) provision(
 	builder := wsbuilder.New(workspace, transition, *c.buildUsageChecker.Load()).
 		Reason(database.BuildReasonInitiator).
 		Initiator(database.PrebuildsSystemUserID).
-		MarkPrebuild()
+		MarkPrebuild().
+		RenderCache(c.renderCache)
 
 	if transition != database.WorkspaceTransitionDelete {
 		// We don't specify the version for a delete transition,
