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actor-ts

prom-client adapter

If your app already uses prom-client (the de-facto Node / Prometheus library) for its non-actor metrics, the PromClientAdapter lets the framework’s metrics live in the same prom-client registry — one /metrics endpoint, all metrics together.

import { Registry } from 'prom-client';
import { ActorSystem, MetricsExtensionId, PromClientAdapter } from 'actor-ts';


const promRegistry = new Registry();
// ... register your existing prom-client metrics ...


const system = ActorSystem.create('my-app');
const metrics = system.extension(MetricsExtensionId);


// Mirror framework metrics into the prom-client registry:
const adapter = new PromClientAdapter({
  source: metrics.registry,
  target: promRegistry,
});


adapter.start();


// Now exposing prom-client's combined export includes framework metrics:
get(async () => ({
  status: 200,
  body: await promRegistry.metrics(),
  contentType: promRegistry.contentType,
}));

The adapter mirrors framework metrics into the prom-client registry on a periodic interval (configurable). Both registries work normally; the adapter syncs values between them.

When to use it

Section titled “When to use it”

Two main reasons:

  1. Existing prom-client usage — your code has been emitting metrics via prom-client; you don’t want to maintain two registries.
  2. One scrape endpoint — your operators expect a single /metrics URL combining all your metrics.

If you don’t already use prom-client, prefer the framework’s native Prometheus exporter — no extra dependency.

Configuration

Section titled “Configuration”
interface PromClientAdapterSettings {
  source:        MetricsRegistry;     // the framework's registry
  target:        Registry;             // prom-client's
  syncIntervalMs?: number;             // default 5000
  prefix?:        string;              // optional name prefix
}

syncIntervalMs is the cadence at which framework values get copied into the prom-client registry. For most scrape setups (every 15-30 s), a 5-second sync is plenty.

prefix lets you namespace framework metrics:

new PromClientAdapter({
  source: metrics.registry,
  target: promRegistry,
  prefix: 'actorts_',
});


// → actorts_http_requests_total, actorts_sessions_active, ...

Peer dependency

Section titled “Peer dependency”
Terminal window
npm install prom-client
# or: bun add prom-client

prom-client is a peer — only required if you use this adapter.

Where to next

Section titled “Where to next”