AWS Architecture Blog

Modernization pathways for a legacy .NET Framework monolithic application on AWS

Organizations aim to deliver optimal technological solutions based on their customers’ needs. Although they may be at any stage in their cloud adoption journey, businesses often end up managing and building monolithic applications. However, there are many challenges to this solution. The internal structure of a monolithic application makes it difficult for developers to maintain code. This creates a steep learning curve for new developers and increases costs. Monoliths require multiple teams to coordinate a single large release, which increases the collaboration and knowledge transfer burden. As a business grows, a monolithic application may struggle to meet the demands of an expanding user base. To address these concerns, customers should evaluate their readiness to modernize their applications in the AWS Cloud to meet their business and technical needs.

We will discuss an approach to modernizing a monolithic three-tier application (MVC pattern): a web tier, an application tier using a .NET Framework, and a data tier with a Microsoft SQL (MSSQL) Server relational database. There are three main modernization pathways for .NET applications: rehosting, replatforming, and refactoring. We recommend following this decision matrix to assess and decide on your migration path, based on your specific requirements. For this blog, we will focus on a replatform and refactor strategy to design loosely coupled microservices, packaged as lightweight containers, and backed by a purpose-built database.

Your modernization journey

The outcomes of your organization’s approach to modernization gives you the ability to scale optimally with your customers’ demands. Let’s dive into a guided approach that achieves your goals of a modern architecture, and at the same time addresses scalability, ease of maintenance, rapid deployment cycles, and cost optimization.

This involves four steps:

  1. Break down the monolith
  2. Containerize your application
  3. Refactor to .NET 6
  4. Migrate to a purpose-built, lower-cost database engine.

1. Break down the monolith

Migration to the Amazon Web Services (AWS) Cloud has many advantages. These can include increased speed to market and business agility, new revenue opportunities, and cost savings. To take full advantage, you should continuously modernize your organization’s applications by refactoring your monolithic applications into microservices.

Decomposing a monolithic application into microservices presents technical challenges that require a solid understanding of the existing code base and context of the business domains. Several patterns are useful to incrementally transform a monolithic application into microservices and other distributed designs. However, the process of refactoring the code base is manual, risky, and time consuming.

To help developers accelerate the transformation, AWS introduced AWS Microservice Extractor for .NET. This helps breakdown architecting and refactoring applications into smaller code projects. Read how AWS Microservice Extractor for .NET helped our partner, Kloia, accelerate the modernization journey of their customers and decompose a monolith.

The next modernization pathway is to containerize your application.

2. Containerize

Why should you move to containers? Containers offer a way to help you build, test, deploy, and redeploy applications on multiple environments. Specifically, Docker Containers provide you with a reliable way to gather your application components and package them together into one build artifact. This is important because modern applications are often composed of a variety of pieces besides code, such as dependencies, binaries, or system libraries. Moving legacy .NET Framework applications to containers helps to optimize operating system utilization and achieve runtime consistency.

To accelerate this process, containerize these applications to Windows containers with AWS App2Container (A2C). A2C is a command line tool for modernizing .NET and java applications into containerized applications. A2C analyzes and builds an inventory of all applications running in virtual machines, on-premises, or in the cloud. Select the application that you want to containerize and A2C packages the application artifact and identified dependencies into container images. Here is a step-by-step article and self-paced workshop to get you started using A2C.
Once your app is containerized, you can choose to self-manage by using Amazon EC2 to host Docker with Windows containers. You can also use Amazon Elastic Container Service (ECS) or Amazon Elastic Kubernetes Service (Amazon EKS). These are fully managed container orchestration services that frees you to focus on building and managing applications instead of your underlying infrastructure. Read Amazon ECS vs Amazon EKS: making sense of AWS container services.

In the next section, we’ll discuss two primary aspects to optimizing costs in our modernization scenario:

  1. Licensing costs of running workloads on Windows servers.
  2. SQL Server licensing cost.

3. Refactor to .NET 6

To address Windows licensing costs, consider moving to a Linux environment by adopting .NET Core and using the Dockerfile for a Linux Container. Customers such as GoDataFeed benefit by porting .NET Framework applications to more recent .NET 6 and running them on AWS. The .NET team has significantly improved performance with .NET 6, including a 30–40% socket performance improvement on Linux. They have added ARM64-specific optimizations in the .NET libraries, which enable customers to run on AWS Graviton.

You may also choose to switch to a serverless option using AWS Lambda (which supports .NET 6 runtime), or run your containers on ECS with Fargate, a serverless, pay-as-you-go compute engine. AWS Fargate powered by AWS Graviton2 processors can reduce cost by up to 20%, and increase performance by up to 40% versus x86 Intel-based instances. If you need full control over an application’s underlying virtual machine (VM), operating system, storage, and patching, run .NET 6 applications on Amazon EC2 Linux instances. These are powered by the latest-generation Intel and AMD processors.

To help customers port their application to .NET 6 faster, AWS added .NET 6 support to Porting Assistant for .NET. Porting Assistant is an analysis tool that scans .NET Framework (3.5+) applications to generate a target .NET Core or .NET 6 compatibility assessment. This helps you to prioritize applications for porting based on effort required. It identifies incompatible APIs and packages from your .NET Framework applications, and finds known replacements. You can refer to a demo video that explains this process.

4. Migrate from SQL Server to a lower-cost database engine

AWS advocates that you build use case-driven, highly scalable, distributed applications suited to your specific needs. From a database perspective, AWS offers 15+ purpose-built engines to support diverse data models. Furthermore, microservices architectures employ loose coupling, so each individual microservice can independently store and retrieve information from its own data store. By deploying the database-per-service pattern, you can choose the most optimal data stores (relational or non-relational databases) for your application and business requirements.

For the purpose of this blog, we will focus on a relational database alternate for SQL Server. To address the SQL Server licensing costs, customers can consider a move to an open-source relational database engine. Amazon Relational Database Service (Amazon RDS) supports MySQL, MariaDB, and PostgreSQL. We will focus on PostgreSQL with a well-defined migration path. Amazon RDS supports two types of Postgres databases: Amazon RDS for PostgreSQL and Amazon Aurora PostgreSQL-Compatible Edition. To help you choose, read Is Amazon RDS for PostgreSQL or Amazon Aurora PostgreSQL a better choice for me?

Once you’ve decided on the Amazon RDS flavor, the next question would be “what’s the right migration strategy for me?” Consider the following:

  1. Convert your schema
  2. Migrate the data
  3. Refactor your application

Schema conversion

AWS Schema Conversion Tool (SCT) is a free tool that can help you convert your existing database from one engine to another. AWS SCT supports a number of source databases, including Microsoft SQL Server, Oracle, and MySQL. You can choose from target database engines such as Amazon Aurora PostgreSQL-Compatible Edition, or choose to set up a data lake using Amazon S3. AWS SCT provides a graphical user interface that directly connects to the source and target databases to fetch the current schema objects. When connected, you can generate a database migration assessment report to get a high-level summary of the conversion effort and action items.

Data migration

When the schema migration is complete, you can move your data from the source database to the target database. Depending on your application availability requirements, you can run a straightforward extraction job that performs a one-time copy of the source data into the new database. Or, you can use a tool that copies the current data and continues to replicate all changes until you are ready to cut over to the new database. One such tool is AWS Database Migration Service (AWS DMS) that helps you migrate relational databases, data warehouses, NoSQL databases, and other types of data stores.

With AWS DMS, you can perform one-time migrations, and you can replicate ongoing changes to keep sources and targets in sync. When the source and target databases are in sync, you can take your database offline and move your operations to the target database. Read Microsoft SQL Server To Amazon Aurora with PostgreSQL Compatibility for a playbook or use this self-guided workshop to migrate to a PostgreSQL compatible database using SCT and DMS.

Application refactoring

Each database engine has its differences and nuances, and moving to a new database engine such as PostgreSQL from MSSQL Server will require code refactoring. After the initial database migration is completed, manually rewriting application code, switching out database drivers, and verifying that the application behavior hasn’t changed requires significant effort. This involves potential risk of errors when making extensive changes to the application code.

AWS built Babelfish for Aurora PostgreSQL to simplify migrating applications from SQL Server to Amazon Aurora PostgreSQL-Compatible Edition. Babelfish for Aurora PostgreSQL is a new capability for Amazon Aurora PostgreSQL-Compatible Edition that enables Aurora to understand commands from applications written for Microsoft SQL Server. With Babelfish, Aurora PostgreSQL now understands T-SQL, Microsoft SQL Server’s proprietary SQL dialect. It supports the same communications protocol, so your apps that were originally written for SQL Server can now work with Aurora. Read about how to migrate from SQL Server to Babelfish for Aurora PostgreSQL. Make sure you run the Babelfish Compass tool to determine whether the application contains any SQL features not currently supported by Babelfish.

Figure 1 shows the before and after state for your application based on the modernization path described in this blog. The application tier consists of microservices running on Amazon ECS Fargate clusters (or AWS Lambda functions), and the data tier runs on Amazon Aurora (PostgreSQL flavor).

Figure 1. A modernized microservices-based rearchitecture

Figure 1. A modernized microservices-based rearchitecture


In this post, we showed a migration path for a monolithic .NET Framework application to a modern microservices-based stack on AWS. We discussed AWS tools to break the monolith into microservices, and containerize the application. We also discussed cost optimization strategies by moving to Linux-based systems, and using open-source database engines. If you’d like to know more about modernization strategies, read this prescriptive guide.

Ramakant Joshi

Ramakant Joshi

Ramakant Joshi is an AWS Solutions Architect, specializing in the analytics and serverless domain. He has a background in software development and hybrid architectures, and is passionate about helping customers modernize their cloud architecture.