fastify-metrics
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Prometheus metrics exporter for Fastify.
This plugin uses prom-client under the hood with optional support for @platformatic/prom-client as a high-performance drop-in replacement.
This plugin also adds two http metrics for your routes:
fastify-1.xfastify-2.x prom-client-11.xfastify-2.x prom-client-12.xfastify-3.xfastify-4.x prom-client-14.xfastify-4.x prom-client-15.xfastify-5.x prom-client-15.xcontext.config with routeConfig due to deprecation in fastify v4 and removal in fastify v5. If you had disableMetrics option in you route config, update fastify to latest version.request.routeOptions.method over deprecated request.routerMethod.metrics from request. Now it uses WeakMap and not exposed.enableDefaultMetrics - now enables only default prom-client metrics. Set to true by default.enableRouteMetrics - additional flag that enables route metrics. Set to true by default.npm i fastify-metrics --save
pnpm i fastify-metrics --save
This plugin supports @platformatic/prom-client as an optional drop-in replacement for prom-client. It is a performance-focused fork by Platformatic that provides the same API with lower overhead ā optimized internal data structures, reduced memory allocations, and faster metric serialization.
If @platformatic/prom-client is installed, the plugin will use it automatically. No configuration changes needed. If it's not installed, the plugin falls back to standard prom-client.
prom-client | @platformatic/prom-client | |
|---|---|---|
| API | Standard | Same (drop-in compatible) |
| Internal storage | hashMap | Optimized LabelMap |
| Memory allocations | Standard | Reduced |
| Metric serialization | Standard | Faster |
| Node.js support | >=16 | ^20 || ^22 || >=24 |
Just install it alongside fastify-metrics:
npm i @platformatic/prom-client
pnpm i @platformatic/prom-client
The plugin auto-detects it on startup. No code changes required.
You can also pass the client explicitly via the promClient option. This takes precedence over auto-detection:
import fastify from 'fastify';
import metricsPlugin from 'fastify-metrics';
import client from '@platformatic/prom-client';
const app = fastify();
await app.register(metricsPlugin, {
endpoint: '/metrics',
promClient: client,
});
After registration, fastify.metrics.client holds the resolved prom-client instance. You can check which one is being used:
await app.ready();
console.log(app.metrics.client); // the active prom-client module
metrics to fastify instance for your custom metrics.>=4.0.0.>=20.0.0.Add it to your project like regular fastify plugin. Use register method and pass options to it.
const fastify = require('fastify');
const app = fastify();
const metricsPlugin = require('fastify-metrics');
await app.register(metricsPlugin, { endpoint: '/metrics' });
It also exports client to fastify instance fastify.metrics.client which you may use it in your routes.
You may create your metrics when app starts and store it in fastify.metrics object and reuse them in multiple routes.
After calling registry.clear() all metrics are removed from registry. In order to add them again to the registry, call fastify.metrics.initMetricsInRegistry.
See for details docs
| Property | Type | Default Value |
|---|---|---|
| clearRegisterOnInit? | boolean | false |
| defaultMetrics? | IDefaultMetricsConfig | { enabled: true } |
| endpoint? | string | null | Fastify.RouteOptions | '/metrics' |
| name? | string | 'metrics' |
| promClient? | prom-client instance | null | null |
| routeMetrics? | IRouteMetricsConfig | { enabled: true } |
| Property | Type | Default Value |
|---|---|---|
| enabled? | boolean | { histogram: boolean, summary: boolean } | true |
| groupStatusCodes? | boolean | false |
| invalidRouteGroup? | string | '__unknown__' |
| methodBlacklist? | readonly string[] | ['HEAD','OPTIONS','TRACE','CONNECT'] |
| customLabels? | Record<string, string | ((request: FastifyRequest, reply: FastifyReply) => string)> | undefined |
| overrides? | IRouteMetricsOverrides | |
| registeredRoutesOnly? | boolean | true |
| routeBlacklist? | readonly (string | RegExp)[] | undefined |
The enabled configuration option can be either a boolean which enables/disables generation of both histograms and summaries, or it can be set to an object that allows you to pick individually whether you want histograms or summaries to be generated, for example:
{
...
routeMetrics: {
enabled: {
histogram: true,
summary: false
}
}
}
would result in the library only generating histograms.
You may override default metrics settings. You may provide overrides for two metrics tracking http request durations: histogram and summary.
const fastify = require('fastify');
const app = fastify();
const metricsPlugin = require('fastify-metrics');
await app.register(metricsPlugin, {
endpoint: '/metrics',
routeMetrics: {
overrides: {
histogram: {
name: 'my_custom_http_request_duration_seconds',
buckets: [0.1, 0.5, 1, 3, 5],
},
summary: {
help: 'custom request duration in seconds summary help',
labelNames: ['status_code', 'method', 'route'],
percentiles: [0.5, 0.75, 0.9, 0.95, 0.99],
},
},
},
});
| Property | Type | Default value |
|---|---|---|
| getRouteLabel? | (request: FastifyRequest) => string | undefined |
| method? | string | 'method' |
| route? | string | 'route' |
| status? | string | 'status_code' |
| Property | Type | Default value |
|---|---|---|
| name? | string | 'http_request_summary_seconds' |
| help? | string | 'request duration in seconds summary' |
| percentiles? | number[] | [0.5, 0.9, 0.95, 0.99] |
| Property | Type | Default value |
|---|---|---|
| name? | string | 'http_request_duration_seconds' |
| help? | string | 'request duration in seconds' |
| buckets? | number[] | [0.05, 0.1, 0.5, 1, 3, 5, 10] |
The following table shows what metrics will be available in Prometheus (subject to the enabled configuration option). Note suffixes like _bucket, _sum, _count are added automatically.
| metric | labels | description |
|---|---|---|
http_request_duration_seconds_count | method, route, status_code | Requests total count |
http_request_duration_seconds_bucket | method, route, status_code | Requests durations by bucket |
http_request_summary_seconds | method, route, status_code | Requests duration percentiles |
http_request_summary_seconds_count | method, route, status_code | Requests total count |
See docs.
See changelog.
If you find this project useful, please consider supporting Ukraine's defense.
Licensed under MIT.
FAQs
Prometheus metrics exporter for Fastify
The npm package fastify-metrics receives a total of 134,390 weekly downloads. As such, fastify-metrics popularity was classified as popular.
We found that fastify-metrics demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago.Ā It has 1 open source maintainer collaborating on the project.
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