Who and how makes the decision on choosing the architectural model: monolith or microservice?

The decision to choose an architectural model — monolith or microservice — is usually made by the development team in collaboration with architects and stakeholders (product managers, business analysts).

The main factors influencing the choice are:

• Size and complexity of the project: small projects often suffice with a monolith, while large projects benefit from microservices to divide responsibilities.
• Team and processes: microservices require more mature DevOps and management processes.
• Scalability and fault tolerance requirements: microservices allow scaling of individual parts of the system.
• Time and resources for development: a monolith is simpler and faster to start.

Ultimately, the choice depends on the balance between flexibility, support complexity, and business requirements. Often, projects start with a monolith and transition to microservices as the system grows.