Monolith vs microservices: when to choose which?

A monolith deploys the whole application as one unit. A microservices architecture splits it into small services that are deployed independently, each owning its data and communicating over the network.

Monolith strengths: simple to build, test, deploy and debug, no network calls between modules, easy transactions, and low operational overhead. It fits a small team, a new product with unclear boundaries, or a modest scale. A well-structured modular monolith keeps clear internal boundaries and can be split later.

Microservices strengths: independent deployment and scaling, team autonomy, fault isolation, and freedom to choose technology per service. The price is distributed-systems complexity: network failures, data consistency without simple transactions, service discovery, observability and a heavy operations burden.

I start with a monolith unless there is a real need, such as many teams blocking each other or very different scaling needs. Microservices solve organizational and scaling problems, not code-quality problems.