MongoDB mongodump

Introduction

Database backups are a critical part of any application's operational strategy. MongoDB provides a powerful utility called mongodump that allows you to create binary exports (backups) of your MongoDB databases, which can later be restored using the mongorestore tool.

In this guide, we'll explore how to use mongodump effectively for various backup scenarios, understand its options, and learn best practices for implementing a solid backup strategy for your MongoDB deployments.

What is mongodump?

mongodump is a command-line utility that creates a binary export of the contents of a MongoDB database. It's part of the MongoDB Database Tools and provides a way to create backups of your collections, which can be used for:

• Creating full or partial database backups
• Migrating data between MongoDB instances
• Setting up development/test environments with production-like data
• Creating archive points for disaster recovery

Basic Usage

The simplest way to use mongodump is to run it without any parameters, which will connect to the local MongoDB instance and back up all databases:

bash

mongodump

By default, this command:

1. Connects to localhost on port 27017
2. Dumps all databases (except local)
3. Outputs the data to the ./dump directory

The output will look similar to:

2023-10-15T12:34:56.789+0000    writing admin.system.version to dump/admin/system.version.bson
2023-10-15T12:34:56.791+0000    done dumping admin.system.version (1 document)
2023-10-15T12:34:56.791+0000    writing myDatabase.users to dump/myDatabase/users.bson
2023-10-15T12:34:56.834+0000    done dumping myDatabase.users (242 documents)
...

Common Options

Let's explore some of the most commonly used options with mongodump:

Specifying a Database and Collection

To back up a specific database:

bash

mongodump --db myDatabase

To back up a specific collection within a database:

bash

mongodump --db myDatabase --collection users

Setting Output Directory

Change the default output directory:

bash

mongodump --out /path/to/backup/directory

Connection Options

When connecting to a remote MongoDB server or one with authentication:

bash

mongodump --host mongodb.example.com --port 27017 --username myUser --password myPassword --authenticationDatabase admin

For MongoDB Atlas or other services using connection strings:

bash

mongodump --uri "mongodb+srv://username:[email protected]/myDatabase"

Creating Compressed Backups

To save disk space, you can create gzipped output files:

bash

mongodump --archive=backup.gz --gzip

Advanced Usage Scenarios

Partial Backups with Queries

You can use queries to back up only specific documents:

bash

mongodump --db myDatabase --collection users --query '{"active": true}'

This backs up only users where the active field equals true.

Point-in-Time Backups

For consistent backups of replica sets, you can use the --oplog option:

bash

mongodump --oplog

This captures all operations during the dump, allowing for point-in-time recovery.

Excluding Collections

Exclude specific collections from the backup:

bash

mongodump --db myDatabase --excludeCollection=logs --excludeCollection=temp

Real-World Examples

Example 1: Daily Backup Script

Here's a simple bash script you might use for daily backups:

bash

#!/bin/bash
# daily-backup.sh

# Variables
BACKUP_DIR="/var/backups/mongodb/$(date +%Y%m%d)"
LOG_FILE="/var/log/mongodb/backup-$(date +%Y%m%d).log"

# Create backup directory
mkdir -p $BACKUP_DIR

# Run mongodump
mongodump --out $BACKUP_DIR --gzip > $LOG_FILE 2>&1

# Delete backups older than 14 days
find /var/backups/mongodb -type d -mtime +14 -exec rm -rf {} \; 2>/dev/null

Example 2: Migrating a Production Database to Development

Sanitizing sensitive data while migrating to a dev environment:

bash

# Step 1: Dump only the essential collections
mongodump --uri "mongodb://prod-server:27017/myApp" \
  --collection users --collection products --collection orders

# Step 2: Restore to development with the mongorestore tool (not covered in this guide)

# Step 3: Sanitize sensitive data directly in development (example MongoDB command)
# db.users.updateMany({}, {$set: {email: "[email protected]", phone: "555-0000"}})

Example 3: Selective Backup Based on Date Range

Backing up transactions from the last month:

bash

mongodump --db finance --collection transactions \
  --query '{"date": {"$gte": {"$date": "2023-09-01T00:00:00Z"}, "$lt": {"$date": "2023-10-01T00:00:00Z"}}}' \
  --out monthly-backup

Common Issues and Solutions

Error: "Failed to connect to..."

If you encounter connection issues:

• Check that MongoDB is running
• Verify network connectivity
• Ensure authentication credentials are correct
• Check firewall settings

Error: "not authorized on admin to execute command..."

This indicates a permissions issue:

• Ensure your user has the correct roles (at least backup role)
• Specify the correct --authenticationDatabase

Large Databases

For very large databases:

• Consider using --collection to break down backups
• Schedule backups during low-traffic periods
• Use compression with --gzip
• Consider using mongodump with shards individually if applicable

mongodump vs. Other Backup Methods

Let's compare different MongoDB backup approaches:

Best Practices

1. Schedule Regular Backups: Automate your backup process using cron jobs or task schedulers.

2. Test Your Backups: Regularly verify that your backups can be restored properly.

3. Use Compression: Especially for large databases, use the --gzip option to save space.

4. Set Retention Policies: Automatically remove older backups to manage storage.

5. Secure Your Backups: Store backups in secure locations and consider encryption.

6. Document Your Backup Strategy: Keep clear documentation on how to restore in case of emergency.

7. Monitor Backup Jobs: Set up alerts for failed backup jobs.

Summary

mongodump is a powerful and flexible utility for backing up MongoDB databases. It allows you to create full or partial backups, with options for compression, filtering, and point-in-time recovery. When combined with proper scheduling and retention policies, it forms the foundation of a robust MongoDB backup strategy.

By understanding how to use mongodump effectively, you can protect your data against loss and facilitate data migration tasks with confidence.

Additional Resources

• MongoDB Database Tools Documentation: MongoDB Documentation
• Learn more about mongorestore for restoring your backups
• For automated backups of MongoDB Atlas clusters, explore Atlas Backup solutions

Exercises

1. Create a backup of a single collection and restore it with a different name.

2. Write a script that does a weekly full backup and daily incremental backups using --oplog.

3. Set up a backup strategy for a database with one large collection (>10GB) and several small ones.

4. Create a backup of documents that match a specific query, then restore only those documents to a test database.

5. Practice creating compressed archives of your backups and extracting specific collections from them.