Instrumenting FeathersJS with Prometheus

src-app.hooks.js

const prometheus = require('./hooks/prometheus')

module.exports = {
  before: {
    all: [prometheus()],
    find: [],
    get: [],
    create: [],
    update: [],
    patch: [],
    remove: []
  },

  after: {
    all: [prometheus()],
    find: [],
    get: [],
    create: [],
    update: [],
    patch: [],
    remove: []
  },

  error: {
    all: [],
    find: [],
    get: [],
    create: [],
    update: [],
    patch: [],
    remove: []
  }
}

src-app.js

...
const prometheus = require('./prometheus')
...
app.configure(prometheus)
...

src-hooks-prometheus.js

module.exports = (options = {}) => {
  return async context => {
    if (context.type === 'before') {
      const labels = {
        path: context.path,
        method: context.method
      }

      context.endTimer = context.app.get('prometheusFeathersRequestsDurationSeconds').startTimer(labels)
    }

    if (context.type === 'after') {
      context.endTimer()
    }

    return context
  }
}

src-prometheus.js

const prometheusClient = require('prom-client')

module.exports = function (app) {
  prometheusClient.collectDefaultMetrics()

  const prometheusFeathersRequestsDurationSeconds = new prometheusClient.Histogram({
    name: 'feathers_requests_duration_seconds',
    help: 'Duration in seconds of Feathers requests',
    labelNames: ['path', 'method'],
    buckets: [0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5, 10]
  })

  app.use('/metrics', (req, res) => {
    res.set('content-type', prometheusClient.register.contentType)
    res.end(prometheusClient.register.metrics())
  })

  app.set('prometheusFeathersRequestsDurationSeconds', prometheusFeathersRequestsDurationSeconds)
}