I have been doing research on micro services. I have used spring boot seeing how simple it is to start with. During my research i have read that is a good approach that every micro service, that is the ones that do data access from a database, have its own database. I am curious how this works when starting multiple instances of that same micro service. Can those instances of the same micro service work with just one database or they also need a separate database? The dilemma for me is the data would be different across multiple databases. How does load balancing micro services work for such situations?
edited after the first 3 comments I appreciate the comments. I feel i was lacking in explaining my thoughts behind this question. I am used to building monolithic applications. I made use of spring and hibernate (hibernatedaosupport) and lately also hibernate envers. I use transaction management of spring to manage the commits and rollback situation of the database. This has worked for me so far. I have started looking into micro services and so far am unable to find a proper explanation of how spring transaction management used with hibernate and envers as a micro service would work with a single database. I can understand just one instance of this micro service working, but i am curious if multiple instances of this micro service would work properly with just one database. Especially considering the fact that hibernate would cache objects of the database for performance reasons, not to mention envers and its actions.
There is no requirement about that micro-service must have a different database, you could share one database across all your micro-services or have one per micro-service. It depends on you and architectural decisions taking into account the different tradeoffs.
If you decide one database per micro-service and you have many instances of the same micro-service. You must use just one database (like with monolith). About your concerns of Hibernate and Cache you must handle the cache in different way, by example using Hazelcast (https://hazelcast.com/use-cases/caching/hibernate-second-level-cache/) or EhCache.
Anyway the design patterns are just best practices with different tradeoffs, you must understand the advantages and disadvantages of every pattern for later take a decision.