Refactoring a monolith to microservices

Truly greenfield development of microservices-based applications is relatively rare. Many organizations that want to adopt microservices already have a monolithic application. As I describe in chapter 13 of my book, the recommended approach is to use the Strangler application pattern and incrementally migrate function from the monolith into services.

Presentations on refactoring

These presentations are good overviews:

About the FTGO monolith

The FTGO monolith (see source code) is the monolithic version of the microservices-based FTGO application. Its goal is to demonstrate how to refactor a monolithic application into services using the Stranger pattern. It’s used as an example in both my book and in my presentations about refactoring.

Refactoring strategies

Chapter 13 of my book describes how to refactor a monolith to microservices. There are two main refactoring strategies:

  • Implement new functionality as services
  • Extract services from the monolith

Let’s look at each one.

Implement new functionality as services

A good way to begin the migration to microservices is to implement significant new functionality as services. This is sometimes easier than breaking apart of the monolith. It also demonstrates to the business that using microservices significantly accelerates software delivery.

Extract services from the monolith

While implementing new functionality as services is extremely useful, the only way of eliminating the monolith is to incrementally extract modules out of the monolith and convert them into services. For example, let’s imagine that the FTGO team wants to improve the efficiency of the business and customer satisfaction by rapidly iterating on the courier scheduling algorithm. It will be a lot easier for them to work on the delivery management logic if it’s a separate Delivery Service. To do that, the FTGO team must separate delivery management from order management and convert it into service.

Extracting the Delivery Service consists of the following the steps:

  1. Split the code and convert delivery management into a separate, loosely coupled module within the monolith
  2. Split the database and define a separate schema for delivery management.
  3. Define a standalone Delivery Service
  4. Use the standalone Delivery Service
  5. Remove the old and now unused delivery management functionality from the FTGO monolith

Before looking at each of these steps, let’s first review the AS-IS code.


Step 0: Review AS-IS code

In the FTGO monolithic application, Order management and Delivery management are intertwined as shown in this diagram.


Read more about the AS-IS architecture.


Step 1: Split the code

The first step is to split the code and convert delivery management into a separate, loosely coupled module within the monolith.


Read more about how the code is split.


Step 2: Split the database

The second step is split the database and define a separate database schema for the ftgo-delivery-service module.


Read more about splitting the database.


Step 3: Define a standalone Delivery Service

The third step of the refactoring process is to define a standalone Delivery Service and deploy it. The service does not, however, handle production traffic. Instead, it can, for example, be tested in production.


Read more about defining standalone Delivery Service.


Step 4: Use the standalone Delivery Service

The fourth step of the refactoring process is to use the standalone Delivery Service.


Read more about how to route production traffic to the Delivery Service.


Step 5: Remove the delivery management functionality from the FTGO monolith

The fifth step of the refactoring process is to remove the now obsolete delivery management logic from the monolith.


Read more about removing the obsolete code.


Signup to get notified

Signup to get notified when more content is added to this page.

About Microservices.io

Microservices.io is brought to you by Chris Richardson. Experienced software architect, author of POJOs in Action, the creator of the original CloudFoundry.com, and the author of Microservices patterns.

Chris helps clients around the world adopt the microservice architecture through consulting engagements, and training classes and workshops.

Learn how to create a service template and microservice chassis

Take a look at my Manning LiveProject that teaches you how to develop a service template and microservice chassis.

New virtual bootcamp: Distributed data patterns in a microservice architecture

My virtual bootcamp, distributed data patterns in a microservice architecture, is now open for enrollment!

It covers the key distributed data management patterns including Saga, API Composition, and CQRS.

It consists of video lectures, code labs, and a weekly ask-me-anything video conference repeated in multiple timezones.

The regular price is $395/person but use coupon WSSEULWL to sign up for $190 (valid until November 30th, 2022). There are deeper discounts for buying multiple seats.

Learn more

Signup for the newsletter


LEARN about microservices

Chris offers numerous resources for learning the microservice architecture.

Training classes

Chris teaches comprehensive workshops, training classes and bootcamps for executives, architects and developers to help your organization use microservices effectively.

Avoid the pitfalls of adopting microservices and learn essential topics, such as service decomposition and design and how to refactor a monolith to microservices.

Delivered in-person and remotely.


Get the book: Microservices Patterns

Read Chris Richardson's book:

Example microservices applications

Want to see an example? Check out Chris Richardson's example applications. See code

BUILD microservices

Ready to start using the microservice architecture?

Consulting services

Engage Chris to create a microservices adoption roadmap and help you define your microservice architecture,


The Eventuate platform

Use the Eventuate.io platform to tackle distributed data management challenges in your microservices architecture.

Eventuate is Chris's latest startup. It makes it easy to use the Saga pattern to manage transactions and the CQRS pattern to implement queries.

ASSESS your architecture

Assess your application's microservice architecture and identify what needs to be improved.

Consulting services

Engage Chris to conduct an architectural assessment.


Self assessment

Alternatively, conduct a self-assessment using the Microservices Assessment Platform.


Join the microservices google group

Posts

24 Jul 2017 » Revised data patterns

Copyright © 2021 Chris Richardson • All rights reserved • Supported by Kong.