Is it necessary for each microservice to have its own separate database?

It is not mandatory for each microservice to have its own separate database, but this is considered a recommended practice in microservices architecture. This approach is called "Database per Service" and provides:

• Data isolation, which reduces the risks of changes in one service affecting others
• Independence in choosing the data storage technology suitable for a specific service
• Simplification of scaling and deployment

However, in some cases, multiple microservices may share a common database, for example, to simplify integration or due to infrastructure constraints. This can lead to tight coupling of services and complicate their independent development.

Example:

// Microservice A uses SQL Server
// Microservice B uses MongoDB
// Each service manages its own database independently