Monolithic Architecture definition
Monolithic architecture is a software design in which an application's user interface, business logic and data access are built and deployed as a single unit, usually backed by one database. All features share one codebase and run in one process, which keeps development, testing and deployment simple, especially for small teams and early products.
How does a monolithic application work?
In a monolith, every feature lives in the same codebase and runs in the same process. When a customer places an order, the checkout code calls the inventory and payment code through ordinary function calls, then writes to one shared database inside a single transaction. The whole application is built into one artifact, such as a JAR file, a Docker image or a deployed Rails or Django app.
Scaling is done by running more copies of the entire application behind a load balancer. This works well for most workloads, because the stateless application tier scales easily and the database is usually the real bottleneck. Many large, successful products, including well-known ecommerce and SaaS platforms, run on carefully structured monoliths.
Advantages and disadvantages
Monoliths are simpler in almost every operational sense: one repository, one build, one deployment, one place to look for logs. Function calls are fast and reliable compared with network calls, and database transactions guarantee consistency without extra patterns. New developers can run the entire system on a laptop.
Problems appear as the codebase and team grow. Without discipline, modules become tangled, so a change in one area breaks another. Builds and test suites slow down, and every release ships everything at once, which forces teams to coordinate. A memory leak in one feature can affect the whole application, and the entire system must use the same language and framework.
What is a modular monolith?
A modular monolith keeps the single deployment but divides the code into well-separated modules with explicit interfaces, each owning its own part of the database. It preserves operational simplicity while preventing the tangled structure that gives monoliths a bad reputation. It also prepares the system for future extraction, since a module with clear boundaries can later become a microservice.
- Group code by business capability, such as billing or catalog, not by technical layer.
- Allow modules to call each other only through public interfaces.
- Give each module ownership of its own tables.
- Enforce boundaries with architecture tests or linting rules.
How do you migrate a monolith to microservices?
Migration should be incremental. The strangler fig pattern places a routing layer in front of the monolith and moves one capability at a time into a new service, sending traffic to it once it is ready while the rest of the system keeps running. Start with a module that has clear boundaries and a concrete reason to separate, such as very different scaling needs.
Before extracting anything, put automated deployment, centralized logging and tracing in place. Otherwise the new services will be harder to operate than the monolith they replaced, and the team will spend its time chasing failures instead of shipping features. Extract the next service only after the first one is stable.
When should you choose a monolith?
A monolith is usually the right starting point for an MVP, a small to mid-size team, or a domain that is still changing quickly. Splitting into services before boundaries are clear often creates the wrong services. Nexzem typically starts new products as modular monoliths and extracts services only when concrete scaling or team-coordination problems appear.