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Command Monitoring

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  • Overview
  • Event Subscription Example
  • Event Descriptions
  • Example Event Documents

Overview

This guide shows you how to monitor the success or failure of commands sent by the driver to your MongoDB deployment.

Read this guide if you need to record command status in your application or want to explore the information provided in these events.

Event Subscription Example

You can access one or more command monitoring events using the driver by subscribing to them in your application. The following example demonstrates connecting to a replica set and subscribing to one of the command monitoring events created by the MongoDB deployment:

const { MongoClient } = require("mongodb");
// Replace the following with your MongoDB deployment's connection
// string.
const uri =
  "mongodb+srv://<clusterUrl>/?replicaSet=rs&writeConcern=majority";
const client = new MongoClient(uri, { monitorCommands:true });
// Replace <event name> with the name of the event you are subscribing to.
const eventName = "<event name>";
client.on(eventName, event => {
  console.log(`received ${eventName}: ${JSON.stringify(event, null, 2)}`);
});
async function run() {
  try {
    await client.connect();
    // Establish and verify connection
    await client.db("admin").command({ ping: 1 });
    console.log("Connected successfully");
  } finally {
    // Ensures that the client will close when you finish/error
    await client.close();
  }
}
run().catch(console.dir);

Note

Command monitoring is disabled by default. To enable command monitoring, pass the monitorCommands option as true to your MongoClient constructor.

Event Descriptions

You can subscribe to any of the following command monitoring events:

Event Name
Description
commandStarted
Created when a command is started.
commandSucceeded
Created when a command succeeded.
commandFailed
Created when a command failed.

Example Event Documents

The following sections show sample output for each type of command monitoring event.

commandStarted

CommandStartedEvent {
  requestId: 1534,
  databaseName: "app",
  commandName: "find",
  address: 'localhost:27017',
  connectionId: 812613,
  command: {
    find: { firstName: "Jane", lastName: "Doe" }
  }
}

commandSucceeded

CommandSucceededEvent {
  requestId: 1534,
  commandName: "find",
  address: 'localhost:27017',
  connectionId: 812613,
  duration: 1586380205,
  reply: {
    cursor: {
      firstBatch: [
        {
          _id: ObjectId("5e8e2ca217b5324fa9847435"),
          firstName: "Jane",
          lastName: "Doe"
        }
      ],
      _id: 0,
      ns: "app.users"
    },
    ok: 1,
    operationTime: 1586380205
  }
}

commandFailed

CommandFailedEvent {
  requestId: 1534,
  commandName: "find",
  address: 'localhost:27017',
  connectionId: 812613,
  failure: Error("something failed"),
  duration: 1586380205
}
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