Single Monolith

A single monolith (also called a simple monolith) is an architecture where the entire application is built and deployed as one cohesive unit. All features, from the user interface to the business logic to the database access layer, live in a single codebase and share a single database. Unlike a modular monolith, there is typically no enforced separation between different parts of the system.

✅ When is it appropriate

A simple monolith is a very good choice if most of the following apply:

  • you are working with a small team (1-3 developers)
  • you are building an MVP or early-stage product
  • the business logic is simple to moderately complex
  • you need to iterate quickly and change direction
  • the infrastructure needs to be simple and low-cost
  • deploying the entire application at once is not a problem

A simple monolith lets a small team focus entirely on building features rather than managing infrastructure, deployment pipelines, or service boundaries. There is less code, fewer moving parts, and everything runs in one process, which makes it much faster to develop and understand in the early stages of a project.

❌ When is it NOT appropriate

A simple monolith stops making sense if:

  • the team grows beyond 5-6 developers
  • the application has multiple strongly distinct domains
  • you need to frequently deploy only part of the system
  • a single change often breaks other parts of the application
  • builds and tests are becoming slow
  • the project aims for long-term and significant growth

As the codebase grows without enforced boundaries, every developer is working in the same large codebase and changes in one area frequently break unrelated areas. Build and test times increase because the entire system must be rebuilt and retested for every change, even a small one, and deploying a single fix requires redeploying the whole application.

👍 Advantages

  • very fast development start
  • simple architecture
  • minimal infrastructure requirements
  • easy testing and debugging
  • easy project orientation (at the beginning)
  • low operational costs

👎 Disadvantages

  • the code can quickly become messy
  • weak or no boundaries between parts of the system
  • changes in one part can affect the entire system
  • poor team scalability: as more developers work in the same codebase without clear boundaries, they increasingly step on each other's work, causing merge conflicts, unintended side effects, and coordination overhead
  • harder transition to more complex architectures without refactoring

🛠️ Typical use cases

  • MVPs and prototypes
  • internal tools
  • small web applications
  • early-stage startups
  • projects with limited budgets
  • systems where development speed is critical

⚠️ Common mistakes (anti-patterns)

  • mixing all logic into a single layer
  • lack of basic modularity in the code
  • "temporary solutions" that become permanent
  • accumulating technical debt (quick, messy solutions that work now but make future changes harder) until the codebase becomes too tangled to evolve safely
  • trying to scale the monolith without refactoring

Without any structure, a monolith can evolve into what is known as a Big Ball of Mud: a codebase where everything is tangled together with no clear organization, where nobody fully understands the whole system, and where any change risks breaking something unexpected.

💡 How to build on it wisely

Recommended approach:

  1. Introduce clear modules and boundaries in the code.
  2. When the codebase starts showing signs of strain (slow builds, frequent unexpected breakage, or multiple developers constantly blocking each other), transition to a Modular Monolith by introducing explicit boundaries between different business areas.
  3. Only then, if needed, extract independent services.

Starting simple and evolving only when there is a concrete reason to do so avoids the most common mistake: over-engineering early. Jumping straight to microservices without first having a well-understood domain and a team large enough to manage independent services introduces far more complexity than most early-stage projects can sustain.

Related topics

Monolith vs. Microservices
Compare all approaches & get a recommendation
→
Microservices
When to use it, common mistakes & best practices
→
Modular Monolith
When to use it, common mistakes & best practices
→

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