One thing you don’t hear enough about in the microservices world is data. There is plenty of info on how your application should be stateless, cloud native, yadayadayada. But at the end of the day, you need to deal with state and store it somewhere.

I can’t blame this blind spot. Data is hard. Data is even harder in a unstable universe where your containers will be killed randomly and eventually. These problems are being tacked though in many fronts and we do our share.

But once you have dealt with the elasticity problem, you need to address a second problem: data evolution. This is even more pernicious in a microservices universe where:

  • The data structure can and will evolve faster per microservice. Remember this individual puppy is supposed to be small, manageable and as agile as a ballet dancer.

  • For your services to be useful, data must flow from one microservice to another without interlock. So they share data structure directly or via copy, implicitly or via an explicit schema, etc. Requiring to release microservices A, B and C together because they share a common data structure is a big no no.

My colleague Edson Yanaga has written a short but insightful book on exactly those problems. How to deal with data in a zero downtime microservice universe. How to evolve your data structure in a safe and incremental way. How do do that with your good old legacy RDBMS. And a few more subjects.

If you are interested in, or embarking in a microservices journey, I recommend you read this focused book. This will make you progress in your thinking.

The cool thing is that this book is free (or rather Red Hat paid the bill). Go grab a copy of Migrating to microservice databases - O’Reilly (you’ll need to register).

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