feat(supervisor): workload create duration histogram with backend and outcome labels (#3928)

Adds a `workload_create_duration_seconds` Prometheus histogram to the
supervisor, observed around the workload manager `create()` call:

- `backend` label: `kubernetes` | `compute` | `docker` — set once from
the configured workload manager
- `outcome` label: `success` | `error` — the per-outcome counts double
as a create error rate

Registered on the supervisor's existing metrics registry, so it's
exposed on the existing `/metrics` endpoint with no config changes.

Notes:
- Covers cold creates only; warm starts and restores return before
reaching `create()`.
- A create may include backend-internal retries, so one observation can
span multiple attempts.
- Fixed low cardinality: 2 active label sets per deployment × 10
buckets.

.server-changes/workload-create-duration-metric.md

@@ -0,0 +1,6 @@
+---
+area: supervisor
+type: improvement
+---
+
+Add a `workload_create_duration_seconds` Prometheus histogram recording the duration and outcome (success/error) of workload manager create calls, labeled by backend (kubernetes/compute/docker). Previously failed creates were only visible as error logs.

apps/supervisor/src/index.ts

@@ -21,7 +21,7 @@ import {
   isKubernetesEnvironment,
 } from "@trigger.dev/core/v3/serverOnly";
 import { createK8sApi } from "./clients/kubernetes.js";
-import { collectDefaultMetrics } from "prom-client";
+import { collectDefaultMetrics, Histogram } from "prom-client";
 import { register } from "./metrics.js";
 import { PodCleaner } from "./services/podCleaner.js";
 import { FailedPodHandler } from "./services/failedPodHandler.js";
@@ -45,11 +45,20 @@ if (env.METRICS_COLLECT_DEFAULTS) {
   collectDefaultMetrics({ register });
 }
 
+const workloadCreateDuration = new Histogram({
+  name: "workload_create_duration_seconds",
+  help: "Duration of workload manager create calls. A create may include backend-internal retries, so one observation can span multiple attempts.",
+  labelNames: ["backend", "outcome"],
+  buckets: [0.05, 0.1, 0.25, 0.5, 1, 2.5, 5, 10, 30, 60],
+  registers: [register],
+});
+
 class ManagedSupervisor {
   private readonly workerSession: SupervisorSession;
   private readonly metricsServer?: HttpServer;
   private readonly workloadServer: WorkloadServer;
   private readonly workloadManager: WorkloadManager;
+  private readonly workloadManagerBackend: "compute" | "kubernetes" | "docker";
   private readonly computeManager?: ComputeWorkloadManager;
   private readonly logger = new SimpleStructuredLogger("managed-supervisor");
   private readonly resourceMonitor: ResourceMonitor;
@@ -151,10 +160,13 @@ class ManagedSupervisor {
       });
       this.computeManager = computeManager;
       this.workloadManager = computeManager;
+      this.workloadManagerBackend = "compute";
+    } else if (this.isKubernetes) {
+      this.workloadManager = new KubernetesWorkloadManager(workloadManagerOptions);
+      this.workloadManagerBackend = "kubernetes";
     } else {
-      this.workloadManager = this.isKubernetes
-        ? new KubernetesWorkloadManager(workloadManagerOptions)
-        : new DockerWorkloadManager(workloadManagerOptions);
+      this.workloadManager = new DockerWorkloadManager(workloadManagerOptions);
+      this.workloadManagerBackend = "docker";
     }
 
     if (this.isKubernetes) {
@@ -493,6 +505,10 @@ class ManagedSupervisor {
                 hasPrivateLink: message.organization.hasPrivateLink,
               });
               recordPhaseSince("workload_create", createStart, undefined);
+              workloadCreateDuration.observe(
+                { backend: this.workloadManagerBackend, outcome: "success" },
+                (performance.now() - createStart) / 1000
+              );
 
               // Disabled for now
               // this.resourceMonitor.blockResources({
@@ -505,6 +521,10 @@ class ManagedSupervisor {
                 createStart,
                 error instanceof Error ? error : new Error(String(error))
               );
+              workloadCreateDuration.observe(
+                { backend: this.workloadManagerBackend, outcome: "error" },
+                (performance.now() - createStart) / 1000
+              );
               this.logger.error("Failed to create workload", { error });
             }
           }