I have 3 micro-services, for example, A, B, C. Services A does some tasks and updates its database accordingly. Same for rest two services.
Suppose services C could not insert to the database because of some error but service A and B updated the database accordingly and this has led to the inconsistencies in the database.
How shall I correctly handle this scenario if -
Thank you for your answers!
For Separate databases you might want to google the SAGA architecture pattern. This helps you to manage transaction accross different microservices each having respective Database. It would take me a lot of space to describe it here, so I think the best advice I can give you is to refer you to this article SAGA Pattern for database per service architecture
First up, in a microservices architecture you should pursue separate databases, or at the very least separated schemas. Sharing data across microservices, as pointed out in comments, would be a microservice anti-pattern.
You can consider a couple of approaches here:
Each microservice updates it's own database and informs the others that an update has taken place. This enables each microservice to align its own database (eventually consistent).
A better approach, if you need coordination, is to create a fourth coordinating microservice whose job is to orchestrate the other three microservices. Research the saga pattern. This is especially useful if you need transactional coordination (i.e. all services must update their databases or none of them). If you think you need transactional coordination think again very carefully - in many (most?) situations eventually consistent is good enough. If you really need transactional then you should research saga and routing slip patterns which include compensation in the event of a failure.
If you need a unified view of the three separate databases then consider another microservice whose job is to create the view (projection) that you need. Let the microservices do the one thing they are good at and that only, if you start to mix concerns in your microservices - well, again it would be an anti-pattern.
A good method of enabling microservice communication is to use a message bus such as RabbitMQ or Azure Service Bus, but there are many other options including Spring Boot.
Given your questions, I would spend some more time researching microservice architectures and the right tools for your project before embarking on a microservices project. A lot of work has been done to ease the complexity of microservices and you would be wise to research the most suitable tool set for you. Nevertheless it will add quite a lot complexity at first but if done right as the project grows it can pay dividends.
You can use RabbitMQ to make message exchange among Micro Services. RabbitMQ will hold all the information on Database Update. So even if a micro service dies before database update then when the microservice will up again, it would look into RabbitMQ and knows what it missed. Thus it can do the database update after recovering from failure.
