Table of contents
1.
Introduction
2.
MongoDB Migration Steps 
3.
Backup Creation 
4.
Restoration
5.
Features of MongoDB Migration
6.
Frequently Asked Questions
6.1.
What is data migration?
6.2.
What is the difference between online and offline data migration?
6.3.
Is it possible to roll back data migration if something goes wrong?
7.
Conclusion
Last Updated: Feb 5, 2025
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MongoDB Migration

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Introduction

Migration is the process by which data is transferred and migrated or moved from one database to another Mongodb database. During migration, it is important to consider whether the source database is online, which means updating deleting, or offline. In terms of online databases, the process like updating, renaming, and making changes in the database.

The migration process depends on various factors online/offline. In this blog, we will learn how to migrate databases by MongoDB migration.

mongodb migration

MongoDB Migration Steps 

Step 1: Install MongoDB

Download and install MongoDB from the official website. Follow the installation instructions for your operating system.


Step 2: Prepare the Data Assuming you have a JSON file named `data.json` with your data:

[
  { "name": "John", "age": 25, "email": "john@example.com" },
  { "name": "Jane", "age": 30, "email": "jane@example.com" }
]


Step 3: Create a New MongoDB Database

import pymongo
client = pymongo.MongoClient("mongodb://localhost:27017/")
# Create a new database
db = client["my_database"]


Step 4: Design the Collection Schema

MongoDB is schemaless, so you don't need to define a strict schema. However, for clarity, we can specify the expected fields.

collection = db["users"]

schema = {
"name": str,
"age": int,
"email": str
}
collection.create_index("name")


Step 5: Import Data into MongoDB

with open("data.json") as f:
data = json.load(f)

collection.insert_many(data)


Step 6: Verify Data Migration

result = collection.find()

for user in result:
print(user)


Step 7: Update Your Application

Assuming you have a Python application that previously used a different database, update it to use MongoDB.

import pymongo

# Connect to the MongoDB server
client = pymongo.MongoClient("mongodb://localhost:27017/")

# Access your database and collection
db = client["my_database"]
collection = db["users"]

user = collection.find_one({"name": "John"})


Step 8: Test the Application

Run thorough tests to ensure that your application works correctly with MongoDB.


Step 9: Optimize Performance

You can analyze query performance and create additional indexes for better performance. For example:

collection.create_index("age")


Step 10: Monitor and Maintain

Implement monitoring tools to keep track of your MongoDB deployment's performance. Regularly backup your data to prevent data loss.

Backup Creation 

MongoDB provides an inbuilt program/functionality called Mongodump to create a backup zip file. The command syntax for creating the backup is as given below:

mongodump --host=" name of host: port number" --username=" name of the user" --password=" associated password for the user" --authenticationDatabase="admin" --db=" name of source database" --collection="Name of the collection" --query="json" --forceTableScan -v --gzip --out ./dump

Sr No. 

Keywords 

Description 

1.

host  This points to the host's address, where the connection will be established. The default is localhost:27017.

2.

username The name of the user with is used to specify the user, which is verified by the MongoDB database.

3.

password The password is associated with a username for authentication to verify whether or not the person is valid.

4.

authenticationDatabase The database where the user is created and authenticated. If not defined, admin database credentials will be assumed.

5.

db The source database to export or create a dump file. If not defined, all databases in the instance are considered.

6.

collection The collection to be backed up. If not defined, all collections in the database are dumped.

7.

query Optional JSON document to restrict and limit the documents to be dumped.

8.

forceTableScan Scans all the data directly to the data store, bypassing the index of the field.

9.

gzip Compresses the output of the command, resulting in compressed .gz files.

10.

out Specifies the directory or folder where the BSON dump files will be written. The default is a new directory named "dump" within the current directory.

Restoration

The restoration process can be done using the following command:

mongorestore --uri="mongodb://name of user:associated password@name of host:port address?authSource=admin" --drop --noIndexRestore


The terminologies used here have the same descriptions as mentioned for backup creation.

Example: Suppose we have a database named "CN" with a collection. To create a backup zip file (dump file), we can use the following command:

sudo mongodump --db CN --out /var/backups/CNbackup/`date +"%m-%d-%y"`


This will create a zip file that can be used as a dump file for restoring the data in other target databases. The restoration command would look like this:

sudo mongorestore --db CN--drop /var/backups/CNbackup/12-09-03/Files

Keywords 

Description 

sudo This command runs Mongorestore with administrative privileges, ensuring it has the necessary permissions to perform the restoration.
mongorestore This is the name of the program used for restoring MongoDB backups. It handles the process of putting the backed-up data into the target database.
–db CN This part defined the name of the target database where the data will be restored; in this case, it is "CN." The restoration will replace the existing data in the "CN" database.
–out/var/backups/CNbackup/ This is the destination where the backup files will be stored. The backup files will be saved in the "CNbackup" folder located in the "/var/backups/" directory.
date +"%m-%d-%y" This command generates the current date in the format "MM-DD-YY" (Month-Day-Year). The resulting date creates a subfolder inside the "CNbackup" folder, with the current date as the folder name.
--drop This option tells the restoration process to drop (delete) the target database ("CN") before restoring the backup. It means that the existing data in the "CN" database will be removed to make way for the data from the backup.
/var/backups/CNbackup/12-09-09/Files This is the location of the backup files. The restoration process will read the data from the files stored in the "/var/backups/CNbackup/12-09-09/Files" folder and put it into the "CN" database.

Features of MongoDB Migration

Migrate-mongo is a powerful tool designed to automate MongoDB database migrations, making it much easier for developers to manage their database. Features of MongoDB Migration are as follows:- 

  • Simple setup and configuration: Getting started with migrate-mongo, the installation and setup process is very easy and user-friendly.
     
  • Version control: Version control means that every change made by the developer to the database is recorded by version control like git version control, allowing developers to keep a record of changes. If something goes wrong or changes need to be undone, they can easily revert to earlier versions just like Ctrl + Z.
     
  • Automated migration scripts: This automation saves developers from manually handling database changes, reducing the risk of human errors and making the overall process more efficient and effective.
     
  • Flexible migrations: Migrate-mongo supports both forward and backward migrations, meaning developers can apply changes to move the database forward, as well as roll back changes if necessary.
     
  • Easy collaboration: When multiple developers work on the same project, coordinating database changes can become more difficult. All the changes made are version-controlled and recorded using Git. 
     
  • Support for multiple environments: Software development involves various stages, from development to testing to production. This helps ensure that database changes are applied consistently across all environments.
     
  • Detailed logging and error handling: Bugs and errors are an inevitable part of the development process. With migrate-mongo, developers can troubleshoot and debug migration scripts easily.

Frequently Asked Questions

What is data migration?

Moving data from one platform to another is known as data migration. It transfers data from one system to another without affecting running programs, and then rerouting all input and output operations to the new device. 

What is the difference between online and offline data migration?

Online migration occurs when we deploy the snapshot and migrate data from older to newer snapshots. Offline migration is required when there are significant differences between the old and new snapshots and online migration is ineffective. 

Is it possible to roll back data migration if something goes wrong?

Depending on the migration strategy and tools used, it may or may not be possible to roll back completely. Careful planning and backup strategies can help minimize risks during migration.

Conclusion

MongoDB Migration is the activity of moving data between different storage types, environments, formats, or computer applications. It is needed when an organization changes its computer systems or upgrades to a newer version of the systems. This solution is usually performed through programs to attain an automated migration.
 

To better understand the topic, you can refer to Introduction to MongoDBSetting up MongoDB, and MongoDB Tutorial.
 

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