Express

Setup

We recommend the Express Middleware exporter. To set up this exporter, just add it s a dependency in your NodeJS package.json

{
  ...
  "dependencies": {
      ...
      "express-prometheus-middleware": "1.2.0"
  }
}

Import the package and add it to the Express app.

...
const promMid = require('express-prometheus-middleware');
...

app.use(promMid({
    metricsPath: '/metrics',
    collectDefaultMetrics: true,
    requestDurationBuckets: [0.1, 0.5, 1, 3, 5, 10],
    /**
     * Uncomenting the `authenticate` callback will make the `metricsPath` route
     * require authentication. This authentication callback can make a simple
     * basic auth test, or even query a remote server to validate access.
     * To access /metrics you could do:
     * curl -X GET user:password@localhost:9091/metrics
     */
    // authenticate: req => req.headers.authorization === 'Basic dXNlcjpwYXNzd29yZA==',
    /**
     * Uncommenting the `extraMasks` config will use the list of regexes to
     * reformat URL path names and replace the values found with a placeholder value
    */
    // extraMasks: [/..:..:..:..:..:../],
    /**
     * The prefix option will cause all metrics to have the given prefix.
     * E.g.: `app_prefix_http_requests_total`
     */
    // prefix: 'app_prefix_',
    /**
     * Can add custom labels with customLabels and transformLabels options
     */
    // customLabels: ['contentType'],
    // transformLabels(labels, req) {
    //   // eslint-disable-next-line no-param-reassign
    //   labels.contentType = req.headers['content-type'];
    // },
  }));

If the request URLs include ids. for e.g. GET /order/1234567, the URLs need to be captured as /order/{id} to avoid metric explosion. In this example, the regexp [0-9]+ which captures all numbers 1234567 can be specified in the extraMasks list of regular expressions.

extraMasks: ['[0-9]+']

You can verify the presence of the following metrics

• http_requests_total

• http_request_duration_seconds_count

• http_request_duration_seconds_sum

• http_request_duration_seconds_bucket

Metrics

Metric	KPI
Requests http_requests_total	Request Rate rate(http_requests_total[5m])
Errors http_requests_total	Error Ratio (server errors) rate(http_requests_total{status=~"5.."}[5m])/ rate(http_requests_total[5m]) Error Ratio (client errors) rate(http_requests_total{statusCode=~"4.."}[5m])/ rate(http_requests_total[5m])
Latency http_request_duration_seconds	Latency Average rate(http_request_duration_seconds_sum[5m])/ rate(http_request_duration_seconds_count[5m]) Latency P99 histogram_quantile ( 0.99, sum(rate(http_request_duration_seconds_bucket[1m]) > 0) by (le) )

Alerts

KPI	Alerts
Request Rate	RequestRateAnomaly
Error Rate	ErrorRatioBreach ErrorBuildup based on a 99.9 SLO
Latency Average Latency P99	LatencyAverageBreach LatencyAverageAnomaly LatencyP99ErrorBuildup

Dashboards

Service KPI Dashboard

This dashboard has the following KPIs from resources and requests:

• Request Rate

• Latency Average

• Latency P99

• Error Rate

• CPU %

• CPU Cores Used

• CPU Throttle

• Memory %

• Memory Bytes

• Disk Usage

• Network Usage