Migrating from monolith to microservices: How can feature flags help?

One of the crucial, but most challenging, steps to transforming a company’s development culture can be to migrate from legacy monolith applications to distributed architectures. These smaller architectures are usually called “microservices.”

In this article, we’ll explore some critical steps for migrating to a distributed system to  accelerate your migration and increase the chances of a successful outcome.

What is Monolith?

Basically, monolithic architecture is the traditional approach to software design you’re probably already familiar with.

The program is built as a single, self-contained unit that functions separately from other applications. 

The code and data are managed in a single, closely connected codebase and database, meaning any changes to the application require an update of the whole system.

While it may be easy to manage code and deploy in the early stages of a project, the monolithic design is often viewed as cumbersome and inflexible. Updates and modifications can be slow and limiting.

It’s for these reasons that a monolith approach can be considered outdated.  More and more companies are opting to move closer towards microservices.

What Are Microservices?

Microservices are a relatively new approach to software development. 

They usually appear when companies break down a monolithic application into smaller, standalone components. These components are called “services.”

Each service is responsible for handling a specific aspect of the application. The services operate independently of one another. 

This way, if one service fails, it won’t affect the functionality of the other services.

Microservices architecture usually includes developing the application as a collection of services. They each come with their own logic and database, and execute specialized functions.

MIcroservices are often characterized by having small services that communicate with one another through defined APIs.

Why do some companies migrate from Monolith to Microservices?

So why do some companies make the switch?

First, one of the most significant drawbacks of monolithic applications is scalability

Monolith components cannot be scaled independently, meaning developers always need to mount the whole application. 

This means more expensive resources and less developer efficiency. These challenges only get worse over time as a company adds layers and layers of management.  

Another major limitation of monolithic applications is reliability

The components of a monolithic application are interdependent. Any minor issue may lead to the breakdown of the entire application. This can lead to significant downtime, which means loss of business revenue.  

Another issue with monolithic applications is tight coupling

Application components are usually tightly coupled inside a single execution. As a result, changes can be difficult to implement. 

All code changes affect the whole system, which could significantly slow down the development process. It  may become too difficult to manage the complex code system within the application.

Monolithic approaches usually require sticking to a single technology. Integrating any new technology would mean rewriting the entire application. Again, this can be expensive, inefficient, and cost a lot of developer time.

How you might use feature flags to help migrate from monolithic architecture to microservices 

Use incremental migration

Untangle your monolith by splitting it into microservices incrementally with the help of feature flags. 

Start by identifying a functional part of the monolith to migrate to a microservice. Create a microservice version of the functional part, wrap it with a feature flag, and redirect traffic to the old version. 

You could then test out the new microservice while keeping the original functionality in place. This progressive rollout reduces risk compared to traditional migrations.

Start with frequently changing areas

Start with areas of your product that you expect to change often. A high rate of change increases your chances of finding opportunities to turn flags off, then migrate. 

Consider areas like high-value geographies, features with a high rate of code change or updates, and potential new releases to segment your product.

Minimize impact on current customers

The system you have today still makes money, so you’ll obviously want to minimize the impact on your current customers. Leverage targeted feature flags to balance value delivery, risk, and priority across your product while you migrate away from the monolith.

If everything works, increase the traffic. If not, revert to the original by turning the flag off. Repeat this process for each functional part, then remove the flag once it’s no longer needed to avoid building up technical debt.

This process follows a pattern called “strangler fig,” where microservice architecture gradually takes over the monolith.

Plan for the last mile

It can be difficult to cut ties with old features that still provide some value. 

Plan for the last mile by considering metrics like the percentage of development cycles dedicated to maintaining old vs. new things. 

You could also look into revenue attributed to legacy systems vs. engineering overhead, or low eNPS scores that cite maintaining legacy systems, as a potential focus areas.

Use a feature flag management tool

To achieve the best results, you should to use a proven dedicated feature flag management solution  to help your team focus on building, testing, and release better software. 

Feature management simplifies and streamlines processes, reduces stress, and minimizes risk to give couples the confidence to innovate. 

By using feature flags, developers can conduct canary tests and deliver features progressively to mitigate risk and avoid unforeseen issues. 

You can target your rollout based on specific user attributes like geographical location, tenant ID, or operating system. This way, you can ensure that new features are delivered smoothly and confidently.


Migrating from a monolith to a microservices architecture can be a complex and risky process. However, by using feature flags, teams can control the rollout and release of new features, test and target specific populations, and minimize the impact of migration. 

If you’re planning a migration to microservices, look into Unleash as your feature management solution.

Share this article