What does "high cohesion" mean inside a service?

High cohesion means that all components inside a microservice perform related tasks and serve one business goal. In other words, the service's logic, data, and functions form a coherent, internally consistent whole.

#The essence

Only the parts that naturally work together should live inside one service. If a service manages orders, it should contain only order-related processes: creation, status, cancellation, history.

#Why this matters

• Improves clarity and resilience of the code: everything needed for one task is in one place.
• Makes maintenance and development easier: changes do not affect other services.
• Makes the system modular: one service equals one logical zone.

#The opposite: low cohesion

When unrelated functions are gathered in one service (for example, orders, users, and payments together), this leads to chaos, complex logic, and a violation of the "one business function, one service" principle.

Summary:

High cohesion means everything inside a service is logically connected and works toward one goal. This makes the service autonomous, easy to understand, and easy to change.