Merge pull request #11680 from overleaf/em-mongo-pool-monitoring

Mongo connection pool monitoring

GitOrigin-RevId: 050e50e7e67061ccbf39a710ca4532eafd423365

libraries/metrics/index.js

@@ -251,4 +251,5 @@ module.exports.http = require('./http')
 module.exports.open_sockets = require('./open_sockets')
 module.exports.event_loop = require('./event_loop')
 module.exports.memory = require('./memory')
+module.exports.mongodb = require('./mongodb')
 module.exports.timeAsyncMethod = require('./timeAsyncMethod')

libraries/metrics/mongodb.js

@@ -0,0 +1,54 @@
+const { Gauge } = require('prom-client')
+
+function monitor(mongoClient) {
+  const labelNames = ['mongo_server']
+  const poolSize = new Gauge({
+    name: 'mongo_connection_pool_size',
+    help: 'number of connections in the connection pool',
+    labelNames,
+    // Use this one metric's collect() to set all metrics' values.
+    collect,
+  })
+  const availableConnections = new Gauge({
+    name: 'mongo_connection_pool_available',
+    help: 'number of connections that are not busy',
+    labelNames,
+  })
+  const waitQueueSize = new Gauge({
+    name: 'mongo_connection_pool_waiting',
+    help: 'number of operations waiting for an available connection',
+    labelNames,
+  })
+  const maxPoolSize = new Gauge({
+    name: 'mongo_connection_pool_max',
+    help: 'max size for the connection pool',
+    labelNames,
+  })
+
+  function collect() {
+    // Reset all gauges in case they contain values for servers that
+    // disappeared
+    poolSize.reset()
+    availableConnections.reset()
+    waitQueueSize.reset()
+    maxPoolSize.reset()
+
+    const servers = mongoClient.topology?.s?.servers
+    if (servers != null) {
+      for (const [address, server] of servers) {
+        const pool = server.s?.pool
+        if (pool == null) {
+          continue
+        }
+
+        const labels = { mongo_server: address }
+        poolSize.set(labels, pool.totalConnectionCount)
+        availableConnections.set(labels, pool.availableConnectionCount)
+        waitQueueSize.set(labels, pool.waitQueueSize)
+        maxPoolSize.set(labels, pool.options.maxPoolSize)
+      }
+    }
+  }
+}
+
+module.exports = { monitor }

libraries/metrics/test/unit/js/mongodb.js

@@ -0,0 +1,89 @@
+const Metrics = require('../../..')
+
+const { expect } = require('chai')
+const prom = require('prom-client')
+
+describe('mongodb', function () {
+  beforeEach(function () {
+    prom.register.clear()
+    this.pool = {
+      totalConnectionCount: 8,
+      availableConnectionCount: 2,
+      waitQueueSize: 4,
+      options: { maxPoolSize: 10 },
+    }
+    this.servers = new Map([['server1', { s: { pool: this.pool } }]])
+
+    this.mongoClient = { topology: { s: { servers: this.servers } } }
+  })
+
+  it('handles an unconnected client', async function () {
+    const mongoClient = {}
+    Metrics.mongodb.monitor(mongoClient)
+    const metrics = await getMetrics()
+    expect(metrics).to.deep.equal({})
+  })
+
+  it('collects Mongo metrics', async function () {
+    Metrics.mongodb.monitor(this.mongoClient)
+    const metrics = await getMetrics()
+    expect(metrics).to.deep.equal({
+      'mongo_connection_pool_max:server1': 10,
+      'mongo_connection_pool_size:server1': 8,
+      'mongo_connection_pool_available:server1': 2,
+      'mongo_connection_pool_waiting:server1': 4,
+    })
+  })
+
+  it('handles topology changes', async function () {
+    Metrics.mongodb.monitor(this.mongoClient)
+    let metrics = await getMetrics()
+    expect(metrics).to.deep.equal({
+      'mongo_connection_pool_max:server1': 10,
+      'mongo_connection_pool_size:server1': 8,
+      'mongo_connection_pool_available:server1': 2,
+      'mongo_connection_pool_waiting:server1': 4,
+    })
+
+    // Add a server
+    this.servers.set('server2', this.servers.get('server1'))
+    metrics = await getMetrics()
+    expect(metrics).to.deep.equal({
+      'mongo_connection_pool_max:server1': 10,
+      'mongo_connection_pool_size:server1': 8,
+      'mongo_connection_pool_available:server1': 2,
+      'mongo_connection_pool_waiting:server1': 4,
+      'mongo_connection_pool_max:server2': 10,
+      'mongo_connection_pool_size:server2': 8,
+      'mongo_connection_pool_available:server2': 2,
+      'mongo_connection_pool_waiting:server2': 4,
+    })
+
+    // Delete a server
+    this.servers.delete('server1')
+    metrics = await getMetrics()
+    expect(metrics).to.deep.equal({
+      'mongo_connection_pool_max:server2': 10,
+      'mongo_connection_pool_size:server2': 8,
+      'mongo_connection_pool_available:server2': 2,
+      'mongo_connection_pool_waiting:server2': 4,
+    })
+
+    // Delete another server
+    this.servers.delete('server2')
+    metrics = await getMetrics()
+    expect(metrics).to.deep.equal({})
+  })
+})
+
+async function getMetrics() {
+  const metrics = await prom.register.getMetricsAsJSON()
+  const result = {}
+  for (const metric of metrics) {
+    for (const value of metric.values) {
+      const key = `${metric.name}:${value.labels.mongo_server}`
+      result[key] = value.value
+    }
+  }
+  return result
+}