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Application Modernization Ultimate Guide

Discover what application modernization is, why it's important, how MongoDB can help and how to get started.

Legacy applications can be the backbone of organizations. They provide value to customers and may or may not bring huge amounts of revenue to companies. Unfortunately, legacy applications also bring with them their own web of challenges: complex, rigid systems that are difficult and daunting to update, expensive infrastructure that is costly to maintain, and an unwieldy deployment process that can lead to infrequent releases.

Modernizing these legacy applications can be critical for the long-term success of organizations. But should organizations take on the cost and effort of modernizing these legacy applications? If so, how?

In this article, you'll discover the answers to the following questions:

What is Application Modernization?

Application modernization (also known as legacy modernization and software modernization) is the process of updating legacy applications to use modern technologies such as programming languages, frameworks, infrastructure, services, and automation. The following are examples of modernizing applications:

  • Refactoring a monolithic application into microservices.
  • Migrating an application from on-premises to the cloud.
  • Replacing infrequent, manual deployments with frequent, automated deployments.
  • Replacing a relational database with a modern database like MongoDB.

Why is Application Modernization Important?

Application modernization is vital for companies with legacy applications who want to innovate quickly and rapidly bring new value to their customers. Developers reported that maintaining legacy systems and technical debt are the number one hindrance to developer productivity at their companies, according to a survey from Stripe and Harris Poll.

Developers and operations engineers who work on legacy applications face many challenges:

  • Updating huge, monolithic applications is difficult due to application complexity.
  • Scaling a highly-used piece of a monolithic application (rather than the entire application) can be problematic if not impossible.
  • Managing infrastructure on-premises can be expensive and time-consuming.
  • Infrequent, manual deployments tend to be large and, therefore, risky.
  • Relational databases have rigid, complex schemas that can slow development time and require application downtime in order to be updated.

These challenges can lead to a product being late to market and missed opportunities.

What are Application Modernization Patterns?

Several application modernization patterns exist. Typically, patterns that require more investment reap higher rewards.

  • Rehost or redeploy. When you rehost or redeploy your application, you typically "lift and shift" the application from an on-premises deployment to a public cloud, private cloud, hybrid cloud, or multi-cloud deployment.
  • Replatform. When you replatform the application, you modernize an aspect or aspects of the application's platform, like the underlying database. Replatforming typically requires some modifications to the code base.
  • Refactor or rearchitect. When you refactor, you update the code base to make improvements to the code itself without changing the application's functionality. Rearchitecting the application could require updating the code base in order to take advantage of modern architectures like containers or microservices.
  • Replace. When you replace the application, you start from scratch with an entirely new code base. One option is to replace the legacy application feature for feature. Another option is to reimagine the application completely, deciding what features to drop and what new features to implement.

What are the Key Technologies for Application Modernization?

Every application's modernization journey will be unique. However, a few technologies frequently appear in the journey:


Teams may choose to containerize their applications, so the applications can be packaged and deployed consistently, regardless of the environment where they are deployed (locally, on-premises, or in the cloud). This consistency can be helpful throughout the entire software development life cycle from development to testing to deployment to support.


Teams may choose to break a huge, monolithic application into several smaller microservices. The microservices architecture provides several benefits including faster time to market, modularity, flexibility, scalability, resiliency, organizational alignment, and reductions in cost.

Serverless functions.

Teams may choose to move their function execution to the cloud using serverless functions. Cloud providers handle running and scaling serverless functions, so developers can focus on writing and calling the functions. Atlas App Services provides serverless function capabilities through Atlas Functions.

The cloud.

Teams may choose to move from managing their own infrastructure and tech stack to using infrastructure and services in a public cloud, private cloud, or hybrid cloud. Teams may also choose to use a multi-cloud strategy to avoid cloud vendor lock-in.


Teams may choose to move from rigid relational databases to more flexible, modern databases like MongoDB. MongoDB databases have flexible schemas that allow for both structured and unstructured data. MongoDB offers self-managed instances or fully-managed instances on multiple cloud providers through MongoDB Atlas. MongoDB also offers the MongoDB Atlas Data Lake so developers can easily query and combine data stored in MongoDB Atlas with data stored in Amazon S3.

CI/CD automation.

Teams may choose to move from infrequent, manual deployments to frequent, automated deployments by implementing CI/CD (Continuous Integration/Continuous Delivery or Continuous Deployment) pipeline automation.

How Do You Modernize Legacy Applications?

Application modernization is a two-phased process: assessment and execution.

In the assessment phase, the team works together to assess the entire application portfolio and understand applications' details. As part of the assessment, applications are rated on factors like technical implementation, interconnectedness with other applications and systems, anticipated return on investment, and drivers for change. If the application receives a high rating, the team performs a deeper evaluation to estimate the application modernization efforts. The team iterates in order to assess all of the applications. Then the team determines prioritization and creates an application modernization roadmap.

Once the assessment phase is complete, the team will begin the execution phase. In this phase, they will follow the application modernization roadmap. They will typically do the following for each application that was selected for modernization:

  • Design and architect the application modernization.
  • Implement the application modernization, which could involve rehosting, redeploying, replatforming, refactoring, rearchitecting, or replacing the application.
  • Validate and test the application outputs.
  • Deploy the modernized application.

Note that the steps in the execution phase could be completed in a waterfall model or iteratively. In the waterfall model, each step is completed for the entire application before going to the next. In the incremental model, each step in the phase is completed for a small piece of the application. Then the steps are repeated again for another small piece of the application.

A rectangle represents the Assessment Phase. Inside of that rectangle are smaller rectangles representing steps in the Assessment Phase: Assess Application Portfolio and Understand Application Detail. An arrow points from the Assess step to the Understand step. The assessment phase has an arrow pointing to another large rectangle representing the Execution Phase. Inside of that rectangle are smaller rectangles representing steps in the Execution Phase: Design Application Modernization, Implement Application Modernization, Validate Application Outputs, and Deploy Modernization Application. The steps are arranged from left to right with arrows between pointing from the step on the left to the step on the right.

The phases of application modernization.

Why Do Enterprises Need Application Modernization?

Enterprises and businesses of all sizes see numerous benefits from application modernization:

  • Increased developer productivity
  • Reduced infrastructure costs
  • Better application performance
  • Faster time to market
  • More frequent releases
  • Increased customer satisfaction and retention

Businesses who choose not to modernize their applications run the risk of being unable to innovate quickly and being left behind.

How Does Application Modernization Work with MongoDB Atlas?

One common type of application modernization involving MongoDB is moving from a legacy, relational database to MongoDB Atlas. MongoDB Atlas is MongoDB's fully managed Database-as-a-Service. Atlas is an easy-to-use and cost-effective modern service with capabilities like auto-scaling, serverless instances, and multi-cloud data distribution. These capabilities allow development teams to focus on their applications without the hassle of managing databases themselves.

When you modernize an application from a relational database to MongoDB, you want to do more than just "lift and shift" your database. Migrating the data from a relational database's table to a MongoDB collection would certainly work, but the application would likely not reap the benefits of using a modern database. Instead, the team should identify how the data will be accessed in the application and create a new, transformed data model. For a detailed comparison of "lift and shift" database migration versus a modernized and transformed database, check out the "Why the MongoDB Intelligent Operational Data Platform?" section of Legacy Modernization.

Development teams have several options for moving data from a relational database to MongoDB:

  • Write a script that transforms the original application data into JSON and then import that data into MongoDB using the mongoimport tool.
  • Use an Extract Transform Load (ETL) tool to migrate the data from a relational database to MongoDB. ETL Vendors like Informatica and Pentaho have created MongoDB connectors specifically for this task.
  • Migrate the data incrementally so that both the legacy database and modernized database run in parallel.

Many development teams have successfully completed the migration process on their own.

When development teams desire external expertise on how to complete the migration, they can work with MongoDB's professional services team to build an Application Modernization Factory. Throughout the process of building the factory, the MongoDB team provides consulting, program governance, and expertise to ensure the migration is successful.

Should You Modernize Your Database to MongoDB?

Modernizing your database to MongoDB can lead to a variety of benefits including:

  • Improved application performance.
  • Reduced costs.
  • Increased developer productivity.
  • Better resilience.
  • Increased scalability.
  • Global data distribution.
  • Freedom from platform lock-in.

But how do you know if putting in the effort of modernizing your database is actually worth it?

The MongoDB Modernization Scorecard allows you to identify which of your legacy applications are good candidates for being modernized to MongoDB. Visit MongoDB Application Modernization Guide to download a copy of the Scorecard.


Application modernization leads to a variety of benefits including increased developer productivity, reduced infrastructure costs, more frequent releases, and faster time to market. Application modernization encompasses a variety of ways to modernize your application including rehosting, redeploying, replatforming, refactoring, rearchitecting, or replacing the application.

If you want to modernize the database in your application, MongoDB Atlas is a great place to start. Visit the MongoDB Application Modernization Guide to get a copy of the Application Modernization Scorecard, see an example schema that was migrated from a relational database, and read the RDBMS to MongoDB Migration Guide. If you'd like professional assistance in your database modernization, check out the Application Modernization Factory.

Don't let competitors leave you in the dust—increase your development team's productivity and get your ideas to market faster by modernizing your database with MongoDB Atlas.


What does application modernization mean?

Application modernization (also known as legacy modernization and software modernization) is the process of updating legacy applications to use modern technologies such as programming languages, frameworks, infrastructure, services, and automation.

How do you modernize a legacy application?

Teams modernize an application by taking the following steps:

  • Designing and architecting the application modernization.
  • Implementing the application modernization, which could involve rehosting, redeploying, replatforming, refactoring, rearchitecting, or replacing the application.
  • Validating and testing the modernized application.
  • Deploying the modernized application.

What are the advantages of modernization?

Application modernization has a variety of advantages including increased developer productivity, reduced infrastructure costs, better application performance, faster time to market, and more frequent releases.

What are application modernization strategies?

Teams can modernize an application by rehosting, redeploying, replatforming, refactoring, rearchitecting, or replacing it.