Which architecture is more reliable: microservices or monolithic application?

It is not possible to definitively say whether microservices or monoliths are more reliable — reliability depends on the context, implementation quality, and support.

A monolithic application is easier to deploy and test, with fewer points of failure, which can increase reliability at the start. However, as the codebase and team grow, maintaining a monolith becomes more difficult, which can lead to errors.

Microservices provide component isolation: the failure of one service does not necessarily affect the entire system. This increases fault tolerance and scalability. But microservices require complex infrastructure (network, orchestration, monitoring), and communication errors between services can reduce reliability.

The choice depends on the project size, team, and requirements for scalability and fault tolerance.