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20.0.0 • Public • Published

fastify-extras 🧩

Reusable plugins for Fastify.

Dependency Management

The following needs to be taken into consideration when adding new runtime dependency for the fastify-extras package:

  • If dependency is an implementation detail, and end consumer is not expected to import and use the dependency directly, it should be a dependency;
  • If dependency needs to be imported and used by consumer directly for it to function properly, it should be a peerDependency.


  • @bugsnag/js;
  • @opentelemetry/api;
  • @opentelemetry/exporter-trace-otlp-grpc;
  • @opentelemetry/instrumentation;
  • @opentelemetry/resources;
  • @opentelemetry/sdk-trace-base;
  • @opentelemetry/sdk-trace-node;
  • @opentelemetry/semantic-conventions;
  • @prisma/instrumentation;
  • @splitsoftware/splitio;
  • fastify-metrics;
  • fastify-plugin;
  • tslib.

Peer Dependencies

  • @fastify/request-context;
  • @fastify/jwt;
  • fastify;
  • newrelic;
  • pino.


RequestContext Provider Plugin

Plugin to:

  • extend existing FastifyRequest with request context by setting the following:
    • logger, an instance of FastifyBaseLogger;
    • reqId, the request-id;
  • store the request-id in Asynchronous Local Storage to be picked up by instrumentation tooling (e. g. OpenTelemetry).

No options are required to register the plugin.

The getRequestIdFastifyAppConfig() method is exported and returns:

  • genReqId, a function for generating the request-id;
  • requestIdHeader, the header name used to set the request-id.

Which can be passed to Fastify during instantiation.

Public Healthcheck Plugin

Plugin to monitor app status through public healthcheck.

Add the plugin to your Fastify instance by registering it with the following options:

  • healthChecks, a list of promises with healthcheck in the callback;
  • responsePayload (optional), the response payload that the public healthcheck should return. If no response payload is provided, the default response is:
    { "heartbeat": "HEALTHY" }

Your Fastify app will reply with the status of the app when hitting the GET / route.

Split IO Plugin

Plugin to handle feature flags in Split IO.

Add the plugin to your Fastify instance by registering it with the following options:

  • isEnabled, if true the plugin will connect to Split IO using the provided apiKey and store data in memory with background syncing;
  • apiKey, your SDK key;
  • debugMode;
  • localhostFilePath (optional), used to utilize the SDK in localhost mode. It corresponds to the full path to a file with the mapping of feature flag name to treatment. apiKey will be automatically replaced with localhost if localhostFilePath is provided.

The plugin decorates your Fastify instance with a SplitIOFeatureManager, which you can inject and use to leverage the following methods:

  • init(), returns a promise that resolves once the SDK has finished loading. It's called automatically when registering the plugin;

  • getTreatment(), returns the proper treatment based on the feature flag name and the key in input. Expected parameters are:

    • key, the ID of the user/account/etc. you're trying to evaluate a treatment for;
    • splitName, the Split IO feature flag name;
    • attributes (optional), a set of Attributes used in evaluation to further decide whether to show the on or off treatment;

    NOTE: If isEnabled is false, getTreatement() will return control to signal disabled treatment.

  • getTreatmentWithConfig(), used to leverage dynamic configurations with your treatment. It accepts the same parameters as getTreatment(), but the response structure is as follows:

    type TreatmentResult = {
      treatment: string
      config: string | null

    NOTE: If isEnabled is false, getTreatementWithConfig() will return control as treatment and null as config to signal disabled treatment.

  • track(), used to record any actions your customers perform. Returns a boolean to indicate whether or not the SDK was able to successfully queue the event. Expected parameters are:

    • key, the ID of the user/account/etc. you're trying to evaluate a treatment for;
    • trafficType, the traffic type of the key;
    • eventType, the event type that this event should correspond to;
    • value (optional), the value to be used in creating the metric;
    • properties(optional), an object of key value pairs that represent the properties to be used to filter your metrics;
  • shutdown(), gracefully shuts down the client.

More info about Split IO can be checked here.

BugSnag Plugin

Plugin to report errors to BugSnag.

Add the plugin to your Fastify instance by registering it with the following options:

Once the plugin has been added to your Fastify instance and loaded, errors will be reported to BugSnag.

Metrics Plugin

Plugin to expose Prometheus metrics.

Add the plugin to your Fastify instance by registering it with the following options:

  • loggerOptions, used to configure the internal logger instance. It can be a boolean or a set of Pino options. By default it is set to false and the logger is disabled;
  • disablePrometheusRequestLogging (optional). By default Fastify will issue an info level log message when a request is received and when the response for that request has been sent. By setting this option to true, these log messages will be disabled. Defaults to true;
  • bindAddress (optional). By default, the server will listen on the address(es) resolved by localhost when no specific host is provided. See the possible values for host when targeting localhost here;
  • errorObjectResolver, a resolver method that, given an err and optionally a correlationID, it will log the error if something goes wrong.

The plugin exposes a GET /metrics route in your Fastify app to retrieve Prometheus metrics. If something goes wrong while starting the Prometheus metrics server, an Error is thrown. Otherwise, a success message is displayed when the plugin has been loaded.

NewRelic Transaction Manager Plugin

Plugin to create custom NewRelic spans for background jobs.

Add the plugin to your Fastify instance by registering it with the following options:

  • isEnabled.

The plugin decorates your Fastify instance with a NewRelicTransactionManager, which you can inject and use to leverage the following methods:

  • start(), which takes a jobName, and starts a background transaction with the provided name;
  • stop(), which takes a jobId, and ends the background transaction referenced by the ID;
  • addCustomAttribute(), which takes attrName and attrValue and records the custom attribute as such defined. attrValue can be a string, a number, or a boolean.

Amplitude Plugin

This plugin facilitates the transmission of events to Amplitude.

To add this plugin to your Fastify instance, register it with the following configurations:

  • isEnabled: A flag utilized to activate or de-activate the plugin.
  • apiKey (optional): This refers to the Amplitude API key which can be procured from your respective Amplitude project.
  • options (optional): To configure Amplitude, please refer to this documentation.
  • apiUsageTracking (optional): You can use this callback to generate an event that will automatically be sent for tracking API usage. Non-specification of this feature will lead to disabling of API tracking.
  • plugins (optional): This feature allows you to expand the plugin's functionality, from altering event properties to relaying to third-party APIs. To learn more, visit this link.

The plugin decorates your Fastify instance with a Amplitude, which you can inject and use the track method on it to send events whenever you need

📘 To ensure optimal functionality with this plugin, you may need to incorporate Amplitude types into your development dependencies.

"@amplitude/analytics-types": "*"

Additionally, you have the option to enhance the safety and accuracy of your events and properties by wrapping your Amplitude instance with AmplitudeAdapter.

📘Check `AmplitudeAdapter.spec.ts for a practical example

UnhandledException Plugin

This plugin provides a mechanism for handling uncaught exceptions within your Fastify application, ensuring that such exceptions are logged and reported. It's especially useful for capturing unforeseen exceptions and provides a controlled shutdown of the Fastify server, thereby ensuring no potential data corruption.

Setup & Configuration

To integrate this plugin into your Fastify instance, follow these steps:

  1. First, import the necessary types and the plugin:
import { FastifyInstance } from 'fastify'
import { unhandledExceptionPlugin, ErrorObjectResolver } from '@lokalise/fastify-extras'
  1. Configure the plugin:

Define your own ErrorObjectResolver to dictate how the uncaught exceptions will be structured for logging. Here's an example:

const myErrorResolver: ErrorObjectResolver = (err, correlationID) => {
  return {
    error: err,
    id: correlationID,

You'll also need to provide an ErrorReporter instance. This instance should have a report method to handle the error reporting logic. For example:

import { ErrorReporter } from '@lokalise/node-core'

const myErrorReporter = new ErrorReporter(/* initialization params */)
  1. Register the plugin with your Fastify instance:
const fastify = Fastify()

fastify.register(unhandledExceptionPlugin, {
  errorObjectResolver: myErrorResolver,
  errorReporter: myErrorReporter,


The plugin accepts the following options:

  • errorObjectResolver (required): This function determines the structure of the error object which will be logged in case of an uncaught exception.

  • errorReporter (required): An instance of the ErrorReporter which will handle reporting of the uncaught exceptions.

Working Principle

When an uncaught exception occurs, the plugin:

  • Logs the exception using the provided errorObjectResolver.

  • Reports the exception using the ErrorReporter.

  • Shuts down the Fastify server gracefully.

  • Exits the process with exit code 1.


  • @lokalise/node-core: For error reporting.

  • fastify: The framework this plugin is designed for.

🚨 It's critical to note that this plugin listens to the process's 'uncaughtException' event. Multiple listeners on this event can introduce unpredictable behavior in your application. Ensure that this is the sole listener for this event or handle interactions between multiple listeners carefully.

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