prom-react

Add Prometheus metrics to your React App. Built on top of promjs and react-performance libraries

Scope and purpose

The main objective of this package is to provide production runtime observability to React frontends, allowing to monitor and alert about operational metrics such as, but not limited to, section loading times, load app errors and so.

To do so, this library offers a MetricsProvider that is built on top of promjs and @shopify/react-performance. With a minimal instrumentation of your code, you can create fancy Grafana dashboards or raise prometheus alerts of your frontend app.

To better understand the purpose and architectural decisions behind this library, please take a look into this article / presentation

It is important to notice that, taking into account Prometheus pull model, this library needs to push metrics into some Prometheus aggregation gateway to make them available. It is recommended to use against a prom-aggregation-gateway instance, but other alternatives might work as well.

Installation

$ yarn add @cabify/prom-react

Usage

Basic usage

First, you'll need to add a MetricsProvider into your app. It is desirable to add it to the root of your app, to make it widely available.

// src/index.tsx
import { MetricsProvider } from '@cabify/prom-react';

const normalizePath = (path: string) => {
  const match = path.match(/\/products\/(\d+)/);
  if (match) {
    return `/products/:id`;
  }
  return path;
};

const AppRoot = () => (
  <MetricsProvider
    appName="my-app-name"
    owner="my-team"
    getNormalizedPath={normalizePath}
    metricsAggregatorUrl="https://some-metrics-aggregator.com/push-metrics"
  >
    <OtherProviders>
      <App />
    </OtherProviders>
  </MetricsProvider>
);

render(<AppRoot />, document.getElementById('app'));

After that, in all your app pages or section root components, you need to add a navigation mark. It is important to notice that all your page component should add usePerformanceMark. If there is a single page that doesn't explicitly call usePerformanceMark(Stage.Complete, 'page-id'), your metric values will show incorrect results. You will notice it for unusual high values for prom_react_navigation_seconds (it will affect to your p99 metrics). See @shopify/react-performance for more info.

// src/pages/Products.tsx
import { usePerformanceMark, Stage } from '@cabify/prom-react'; // handy re-export of @shopify/react-performance utils

export const Products = () => {
  // whatever way to load the page data
  const [products, isLoading] = useFetchProducts();

  usePerformanceMark(isLoading ? Stage.Usable : Stage.Complete, 'products');

  return '...';
};

If you want also to monitor your app load failures (missing bundle files, js errors at boot time, etc), you'll need to add the following small snippet to your index.html file (it must be placed there so it will execute even if your bundle is unreachable / not working):

window.__PROM_REACT_LOAD_FAILURE_TIMEOUT__ = setTimeout(function () {
  var xhr = new XMLHttpRequest();
  var str = '# HELP prom_react_app_loaded Application loaded counter\n';
  str += '# TYPE prom_react_app_loaded counter\n';
  str += 'prom_react_app_loaded{app_name="<<APP_NAME>>",status="failure"} 1\n';

  xhr.open('POST', '<<METRICS_AGGREGATOR_URL>>');
  xhr.setRequestHeader('Content-Type', 'text/plain');
  xhr.send(str);
}, 3000);

(Please remember to replace <<METRICS_AGGREGATOR_URL>> and <<APP_NAME>> placeholders to match your configuration)

Adding such instrumentation will provide these golden metrics out of the box:

• prom_react_app_loaded: Application loaded counter. It will observe both succesful / failure loads.
• prom_react_app_unloaded: Application unloaded counter. Uses navigator.sendBeacon API behind the scenes.
• prom_react_performance_seconds: Histogram to store load performance event timings (dcl, ttfb, ttfp, etc.).
• prom_react_navigation_duration_seconds: Histogram to store navigation times between sections. It includes both full page loads (navigation_type="full_page) and in-app navigations via history pushState or react-router (navigation_type="in_app). It also includes a label with the path (you need to take care about cardinality explosion by using getNormalizedPath prop when creating MetricsProvider)
• prom_react_ttc_seconds: Histogram to store page TimeToComplete navigation times. It includes same labels as navigation_duration_seconds metric.
• prom_react_ttu_seconds: Histogram to store page TimeToUsable navigation times. It includes same labels as navigation_duration_seconds metric.

Adding custom metrics

You can add your custom app metrics to use them when needed. To do so, just attach them to MetricsProvider. Later on, you can take advantage of useMetrics hook to add observations on those metrics:

// src/index.tsx

import { MetricsProvider } from '@cabify/prom-react';

// please remember to define them outside the component to avoid unneeded re-renders
const customMetrics: MetricDefinition[] = [
  {
    type: 'counter',
    name: 'my_app_report_download_count',
    description: 'Number of reports downloaded',
  },
];

const MyApp = () => {
  return (
    <MetricsProvider appName="MyApp" customMetrics={customMetrics}>
      ...
    </MetricsProvider>
  );
};

// Any inner component
import { useMetrics } from '@cabify/prom-react';

const ReportsDownloadButton = () => {
  const { observe } = useMetrics();

  const downloadReport = () => {
    observe('my_app_report_download_count', { custom_tag: 'custom value' }, 1);

    // your app code
  };

  return <div onClick={downloadReport}>Download report</div>;
};

API

MetricsProvider

React component that configures all the monitoring infrastructure and add the aforementioned golden metrics. It must be placed in the root of your component tree.

Props:

• appName: string;: Name of the app. All metrics will include a label 'app_name' with this value.
• owner?: string;: Owner of the app. All metrics will include a label 'owner' with this value.
• metricsAggregatorUrl?: string;: Url of the push gateway aggregator. If not set, metrics will be collected but not sent.
• customMetrics?: MetricDefinition[];: Custom application metrics. Please define in a const outside the component to avoid infinite loops trying to create them.
• fetchOptions?: Partial<RequestInit>: Extra fetch options (headers, credentials, etc) to be used when sending metrics to the aggregator.
• getNormalizedPath?: (path: string) => string;: Given that all route change metrics include a 'path' label, you should add this function to avoid cardinality issues if you have parameterized routes (ex: /products/:id). See recipes section for examples.
• histogramBuckets?: number[]: Bucket list for the histogram metrics. Defaulted to [0.01, 0.1, 1, 2, 3, 4, 5, 7, 10, 15].

usePerformanceMark, Stage, etc.

This library re-exports all @shopify/react-performance to avoid explicitly add it to your package dependencies. You can have a look at its API documentation for further details.

MetricsLogger

React component that will log into console all metric observations. It won't render anything in the screen. You should not add this in production.

Props:

• logger?: ObserveCallback: If set, it will replace the original logger. Ensure the reference of this value doesn't change between renders by memoizing the logger function or defining it outside the component to avoid performance issues.

MetricsDebugOverlay

React component to show metrics debug info. Must be placed under MetricsProvider. It shows a not-so-fancy overlay with navigation info. It is useful to check if all your sections are properly instrumented with usePerformanceMark. It can also log all your observations to console (uses MetricsLogger under the hood). You should not show this in production.

Props:

• onClose?: () => void: If set, it will show a close button which will call this callback when pressed
• withLogger?: boolean: If set to true, it will include a MetricsLogger. This way, you can have all debugging facilities at hand by only adding this component.

Note that these debug components are very basic and may not fit your needs. However, as all metric data is available through useMetrics hook, you can build your own logger, debugging panel, etc. within your application or as an external library.

useMetrics()

Hook to access metrics registry and some other ready-to-use helpers. It returns an object with the following properties:

• observe(metricName, tags?, value?, skipSending?): Helper to add an observation to an existing metric. Note that the metric should be created in the provider. It supports both histogram and counter metrics.
  • metricName: string: Name of the metric to add observation to.
  • tags?: Record<string, string>: Optional tags to add to the observation. All observations added with this method will have app_name and owner labels properly set.
  • value?: number: Value to add to the observation. It is mandatory for histogram metrics and optional for counter metrics. If not set, this method will increase the counter by 1.
  • skipSending?: boolean: If set to true, the observation will not be sent to the backend (you can call sendMetrics() manually to send observations).
• isReady: boolean: flag to indicate when metrics are ready to be used. You should only rely on this flag if you are planning to add observations to custom metrics when first rendering the app. The rule of thumb here is: only use it if your metric observation raise a warning of "this metric does not exist".
• sendMetrics: () => void: Send metrics to the server. Note: by default, this method is called automatically by observe, but you can call it manually if you skip automatic metric send.
• histogramBuckets: number[];: Buckets for histograms configured in the provider. Included here only for testing purposes, it won't be usually needed.
• navigationData: NavigationData | null: Last navigation data.
• addObserveListener: (callback: ObserveCallback) => void;: Add a listener called whenever an observation is added to the registry.
• removeObserveListener: (callback: ObserveCallback) => void;: Remove observe listener
• registry: Registry: promjs regisry instance. You should not use this directly, but use observe instead. It is exposed for some extremely rare cases and testing purposes.

Recipes

Debugging

If you want to check if your metrics are being generated properly, you can add the MetricsLogger into your component tree and all metric observations will be shown in the console.

const AppRoot = () => (
  <MetricsProvider
    appName="my-app-name"
    owner="my-team"
    getNormalizedPath={normalizePath}
    metricsAggregatorUrl="https://some-metrics-aggregator.com/push-metrics"
  >
    <MetricsLogger />
    <MyApp />
  </MetricsProvider>
);

This will produce log entries like this:

[prom_react] prom_react_navigation_duration_seconds 1.2456 {app_name: 'my_app', path: '/app', navigation_type: 'full_page' }

You can customize the output for MetricsLogger by replacing the original loader:

const metricsLogger = ({ metricName, value, tags }) => {
  console.debug('Custom log for prom-react!', metricName, value, tags);
};
const AppRoot = () => (
  <MetricsProvider
    appName="my-app-name"
    owner="my-team"
    getNormalizedPath={normalizePath}
    metricsAggregatorUrl="https://some-metrics-aggregator.com/push-metrics"
  >
    <MetricsLogger logger={metricsLogger} />
    <MyApp />
  </MetricsProvider>
);

Moreover, you can also add a widget that will show last navigation event being triggered. This is particularly useful to check if all your pages are properly instrumented (you should navigate across your app and the widget should show the right path after every section change).

const AppRoot = () => (
  <MetricsProvider
    appName="my-app-name"
    owner="my-team"
    getNormalizedPath={normalizePath}
    metricsAggregatorUrl="https://some-metrics-aggregator.com/push-metrics"
  >
    {process.env.NODE_ENV !== 'production' && (
      <MetricsDebugOverlay withLogger onClose={closeOverlay} />
    )}
    <MyApp />
  </MetricsProvider>
);

Configure your grafana dashboards and prometheus alerts

• Average active sessions in a given time range:

increase(prom_react_app_loaded{app_name="$job", status="success"}[$__range]) -
on() increase(prom_react_app_unloaded{app_name="$job"}[$__range])

• Load app error rate:

rate(prom_react_app_loaded{app_name="$job",status="failure"}[$__rate_interval]) /
rate(prom_react_app_loaded{app_name="$job"}[$__rate_interval])

• Nth quantile of full page load duration in seconds:

histogram_quantile($quantile,
sum(sum(rate(prom_react_navigation_duration_seconds_bucket{app_name="$job",navigation_type="full_page"}[$__rate_interval])
)
by (le, path)) without(path))

• Page RPS by path:

sum by (path)(rate(prom_react_navigation_duration_seconds_count{app_name="$job"}[$__rate_interval]) != 0)

• (Prometheus alert). Application load failed:

ALERT AppLoadFailed
  IF     rate(prom_react_app_loaded{app_name="my-app",status="failure"}[5m]) /
         rate(prom_react_app_loaded{app_name="my-app"}[5m]) > 0.1
  FOR    15m
  LABELS {...}
  ANNOTATIONS {...}

getNormalizedPath with routes object

If you have your routes defined in a global object like (that you later use in your react router configuration, for instance):

const Urls = {
  INDEX: '/app',
  PRODUCTS: '/app/products',
  PRODUCT_DETAIL: 'app/product/:id',
  ...
}

You can easily create a getNormalizedPath function by:

import { pathToRegexp } from 'path-to-regexp';

const urlRegExps = Object.values(Urls).map((url) => ({
  regExp: pathToRegexp(url),
  url,
}));

export const getNormalizedPath = (url: string) => {
  return urlRegExps.find(({ regExp }) => regExp.test(url))?.url || url;
};

Add authorization header to gateway requests

// src/index.tsx
import { MetricsProvider } from '@cabify/prom-react';

const gatewayFetchOptions = {
  headers: {
    Authorization: `Basic ${btoa('login:password')}`,
  },
};

const AppRoot = () => (
  <MetricsProvider
    appName="my-app-name"
    owner="my-team"
    fetchOptions={gatewayFetchOptions}
    metricsAggregatorUrl="https://some-metrics-aggregator.com/push-metrics"
  >
    <App />
  </MetricsProvider>
);

Automatically check that all your pages include navigation marks

If you can identify your pages root components easily by their file name (for instance if they are always named <SectionName>Page.tsx), it is easy to add a simple shell script to automatically check that all of them are properly instrumented. This way you can avoid wrong navigation metric values (you can also add such script to your CI pipelines or pre-commit scripts just to make sure an instrumented code doesn't reach production). As an extra tip, if there are files that match your page name structure but are not pages (or the page is instrumented somewhere else), you can add an ignore coment à la eslint (ex. // prom-react-ignore).

echo "Checking if all pages are using 'usePerformanceMark'"

OUTPUT=$(grep --include='*Page.tsx' -Lr 'usePerformanceMark\|prom-react-ignore' .)

if [ -z "$OUTPUT" ]; then
    echo "Everything ok"
else
    echo "There are pages that are not using 'usePerformanceMark'"
    echo "$OUTPUT"
    echo "Please start using 'usePerformanceMark' on them or add // prom-react-ignore to ignore that file"
    exit 1
fi

Contributing

• Running tests and linting: yarn test
• Build project: yarn build

Publish a new version

• Update CHANGELOG with new features, breaking changes, etc
• Check you're in main branch and everything is up-to-date.
• Run yarn publish:<major|minor|patch> or yarn publish:canary for canary versions.
• Run git push && git push --tags
• Check all test actions triggered after previous push are ✔️.
• Go to create a new release, select previously pushed tag and write a Title.
• Check the action for publish the npm has finished with success.
• Check on npm package webpage, the version has been published successfully under latest tag.

Contributors ✨

Thanks goes to these wonderful people (emoji key):

This project follows the all-contributors specification. Contributions of any kind welcome!