Monolithic vs Microservices

The monolith vs microservices debate is one of the most important early decisions in software design. Pick the wrong one, and you either fight a tangled codebase for years or spend months building infrastructure before you have a single customer.

This guide explains both approaches in plain English, compares them side by side, shares real stories from Netflix, Shopify, and Amazon, and gives you a simple checklist to decide. It also covers the middle path most teams overlook: the modular monolith.

What Is Monolithic Architecture?

A monolithic application is built as one single program. The user interface, business logic, and data access code all live in one codebase, run in one process, and are deployed together.

A simple way to picture it: a monolith is like a department store. Everything is under one roof, with one entrance and one set of staff. It is easy to run and easy to find things, but if you want to expand the shoe section, you have to expand the whole building.

Inside a good monolith, code is still organized into layers and modules. “Monolith” describes how the app is deployed, not whether the code is messy.

What Is Microservices Architecture?

A microservices application is split into many small services. Each one handles one business area, such as payments, users, or search, owns its own data, and talks to other services through APIs or events. Each service can be built, tested, deployed, and scaled on its own.

The same picture: microservices are like a street of specialty shops. Each shop has its own door, staff, and hours, and you can expand the busy bakery without touching the bookstore. But now you need roads, signs, and deliveries between shops, and someone has to keep the whole street running.

Because services communicate over the network, well-designed APIs are at the heart of every microservices system.

The Middle Path: The Modular Monolith

A modular monolith is still deployed as one app, but the code is split into strict, independent modules with clear boundaries, such as Orders, Billing, and Catalog. Modules talk to each other only through defined interfaces, not by reaching into each other’s code or tables.

It gives you most of the simplicity of a monolith with much of the organization of microservices. And if one module later needs to scale on its own, you can lift it out as a service with far less pain. For a wider look at all the patterns, see our guide to backend architecture.

Monolithic vs Microservices: Side-by-Side Comparison

Pros and Cons of Monolithic Architecture

Pros and Cons of Microservices Architecture

Real-World Examples

Netflix moved to microservices for scale and reliability. In 2008, a major database corruption stopped Netflix from shipping DVDs for about three days. That pushed the company to move from its single data center and monolithic system to the cloud on AWS, rebuilt as many independent services. The move took years and needed huge investment in tooling, which is why Netflix also built and open-sourced much of its own infrastructure software.

Shopify chose a modular monolith. Instead of breaking up its large Ruby on Rails application, Shopify split it into clearly separated components inside one codebase. This shows that a monolith can power a very large business when it is well organized.

Amazon Prime Video moved one tool back to a monolith. In 2023, the Prime Video team reported that combining a distributed video-monitoring tool into a single service cut its infrastructure cost by about 90% and helped it scale better.

Segment went back to a monolith, too. In 2018, Segment’s engineers wrote about merging more than 100 small services back into one, because the overhead of running them all had slowed the team down.

The lesson: Neither approach is “modern” or “old”. Each fits a different stage, team size, and workload.

When to Choose Each Architecture

Choose a monolith (ideally modular) when:

• You are building an MVP or launching a new product. Our guide to what an MVP is explains why speed matters most at this stage.
• Your team has fewer than about 10 to 20 developers.
• Your requirements are still changing quickly.
• You need to keep cloud and DevOps costs low.
• Your traffic is predictable and can be handled by scaling the whole app.

Choose microservices when:

• Several teams need to ship independently without blocking each other.
• Parts of the system have very different scaling needs, such as video processing versus user profiles.
• You need to isolate high-risk areas, such as payments, for reliability or compliance.
• You already have strong CI/CD, container, and monitoring practices.
• Your domain is well understood, so service boundaries will not keep changing.

Quick Decision Checklist

Count how many of these are true for your project:

• ☐ We have more than 3 teams working on the same product
• ☐ Some features need 10x more capacity than others
• ☐ Deploying one change currently blocks other teams for days
• ☐ We have DevOps engineers and container experience in-house
• ☐ Our product’s main features and boundaries are stable
• ☐ We can afford higher cloud and monitoring costs

0 to 2 checked: stay with a monolith, and make it modular. 3 to 4: split out only the one or two services that clearly need it. 5 to 6: microservices are likely a good fit.

If you are missing the DevOps foundation, start there first. Our DevOps team often sets up CI/CD, containers, and monitoring before any split.

How to Move From a Monolith to Microservices

Never rewrite everything at once. The safest approach is the strangler fig pattern: you grow new services around the old app and slowly replace it piece by piece.

1. Make the monolith modular first. Draw clear boundaries between areas like Orders, Billing, and Users.
2. Add monitoring and CI/CD. You need logs, metrics, tracing, and automated deployments before running many services.
3. Pick the first service carefully. Choose an area that changes often or needs to scale on its own, but is not tangled with everything else. Notifications or search are common first picks.
4. Put a gateway or router in front. Send requests for that feature to the new service while everything else still goes to the monolith.
5. Give the service its own data. Move its tables out of the shared database so services do not stay secretly linked.
6. Repeat, one service at a time. Measure the benefit after each step. Stop when the remaining monolith works well.

Larger migrations like this are where an experienced partner saves time and risk. Learn about our platform migration services.

Common Mistakes to Avoid

• Building a “distributed monolith”. Services that share one database or must be deployed together give you the costs of microservices with none of the benefits.
• Making services too small. Dozens of tiny services for a small app create more network calls and more things to monitor than real value.
• Splitting before you understand the business. Wrong service boundaries are expensive to fix later.
• Skipping observability. Without distributed tracing, finding the cause of a slow request across services becomes guesswork.
• Ignoring timeouts and fallbacks. One slow service can cascade into a full outage.
• Calling every big app a bad monolith. Many large, successful products run on well-organized monoliths.

Conclusion

Monolithic and microservices architectures are both valid tools. A monolith, especially a modular one, is usually the fastest and most affordable way to build and launch. Microservices shine when many teams need to move independently and parts of the system need to scale on their own, but they come with real costs in complexity and operations.

Start simple, organize your code into clear modules, invest in DevOps early, and split services out only when you have a clear, measurable reason.

Frequently Asked Questions

What is the main difference between monolithic and microservices architecture?

A monolithic app is built and deployed as one unit with one codebase. A microservices app is split into many small services that are built, deployed, and scaled independently and communicate through APIs.

Are microservices better than monolithic?

Not by default. Microservices are better for large systems with many teams and very different scaling needs. Monoliths are better for most new and small to mid-size products because they are simpler, faster to build, and cheaper to run.

What is a modular monolith?

A modular monolith is one deployable app whose code is divided into strict, independent modules. It keeps the simplicity of a monolith while making it much easier to split into microservices later.

Are microservices more expensive?

Usually, yes. You need more servers or containers, more networking, more monitoring tools, and engineers with DevOps skills. The extra cost pays off only when the benefits, like independent scaling and team speed, are significant.

When should a startup use microservices?

Rarely at the start. Most startups should launch with a modular monolith, find product-market fit, and move specific parts to services when real scaling or team problems appear.

Can you move from a monolith to microservices?

Yes. The safest way is gradually, using the strangler fig pattern: make the monolith modular, then extract one service at a time while the rest of the app keeps running.

Do microservices need Docker and Kubernetes?

Not strictly, but containers like Docker and an orchestrator like Kubernetes, or a managed service such as Amazon ECS, make running many services far more practical. Serverless functions are another option for some services.