Monolithic n-layer architecture

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Monolithic n-layer architecture

Nicola Sergio 60

Hi everyone,

As discussed in this document, an application that has only one project within the solution is considered a monolith.

As discussed in the example this could be considered a 1-layer, 1-tier monolith or 1-layer 3-tier monolith?

How would the project structure change in the case of a modular monolith? How would it change?

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Answer 1

Bruce (SqlWork.com) 76,256 Moderator

N-tier refers to many devices the application components can be spreaded across. The sample is a 1 tier (while the database is actually a tier, it usually isn’t counted), multiple layer app. It has 3 or 4 layers depending on how you count. A typically 2-tier website would have a webapi application and a web ui application. If microservices are used, each is a tier.

while the sample has multiple layers, because they are all in the same project, it’s easy for a lower layer to access a higher layer without a formal adapter. Making each layer is own project prevents this from happening.

when building websites, allowing the exposed ui website direct access to database and other resources is considered a security risk. The ui site should call another service, to access the resources. So for security your site should be 2-tier.

Nicola Sergio 60 Reputation points

2025-05-08T20:46:35.02+00:00

@Bruce (SqlWork.com) ) So that example has 1 layer and 2 tier beacuse of client code is downloaded by users devices. 1 layer because of we have a single project and UI/BL e Data Acess Layer is in the same project. Are my sentences correct?
Pradeep M 8,660 Reputation points Microsoft External Staff Moderator

2025-05-09T12:35:49.9666667+00:00

You're mostly correct, but let me clarify:

The example is considered a 1-tier monolith because all parts of the application (UI, business logic, and data access) run together on the same server. While it has multiple logical layers, they are all contained within a single project. Because of that, there’s no strict separation between layers, which is why it’s sometimes referred to as a 1-layer monolith in terms of structure.

In summary: Tier refers to how components are deployed and run.

Layer refers to how the code is logically organized.
Nicola Sergio 60 Reputation points

2025-05-09T14:36:37.5566667+00:00

@Pradeep M ok so It is wrong saying that client is runned on another tier (client devices)?
Bruce (SqlWork.com) 76,256 Reputation points Moderator

2025-05-09T16:18:31.6166667+00:00

no, its not wrong. websites are really 2 tier (client/server). but when taking the application architecture of website, we typically mean the tiers of the application hosting. Database servers are technically a tier, but we typically don't count them as a tier when defining the application architecture.
Nicola Sergio 60 Reputation points

2025-05-10T08:41:36.8666667+00:00

ok, so the first one example is 1-tier 1-layer monolith (all is deployed on single server and we don't have layers separation because of we have one project only).

Is it correct? @Bruce (SqlWork.com)
Bruce (SqlWork.com) 76,256 Reputation points Moderator

2025-05-13T21:39:36.3933333+00:00

while a single project be be designed n-layer, it easy to break rules. for example a lower layer can call a method in a higher layer directly, while in proper design it should be done via a callback registered by the higher layer.

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