What are the criteria for when to start breaking down a monolith into microservices?

Deciding to break down a monolith into microservices should begin when:

• Code complexity and scale are increasing: the monolith becomes too large, difficult to maintain and develop.
• Development teams are growing and splitting: different teams want to work independently to avoid blocking each other.
• Independent scaling is required: different parts of the system have different load requirements.
• Flexibility in technologies is needed: different services may use different technologies and databases.
• Frequent releases and updates: microservices allow updating parts of the system without a full deployment.
• Reliability issues: a failure in one part of the monolith affects the entire system.

It is important to remember that transitioning to microservices is a complex process that requires mature infrastructure (CI/CD, monitoring, orchestration) and a DevOps culture. If the monolith is currently handling the load and development well, premature transition may lead to unnecessary complexity.

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Criteria to start:

• Monolith is too large (>1 million lines of code or many modules).
• Frequent conflicts during code merging.
• Different parts of the application have different life cycles and requirements.
• The need to scale specific functions.

If these signs are present, it is worth planning decomposition.