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Mark Little

Microservices and events

Posted by Mark Little Apr 25, 2015

OK it's Saturday night (my time) and I've spent the last week travelling across the Atlantic for meetings so have had a bit of time to think on a few things. One of them is how reactive platforms and microservices fit together. I took the time to write down some of what I've been thinking. I think frameworks such as Vert.x and Node.js have a lot to offer microservices and other use cases, but as Robert Frost once said we still have "miles to go before I sleep". That is good because it means there's a lot of exciting research and development still to be done, building on the work of others such as Fischer, Lynch and Paterson.

I've had a few conversations with different people recently on the subject of microservices and (distributed) transactions. One of my biggest worries about microservices in general is that we end up repeating the same conversations and disagreements that we had with SOA, REST and other related technologies. And one of the longest running debates we had during those specific waves was around transactions and their applicability, or not. I continue to believe that transactions are useful for some SOA-based services, though that doesn't mean they have to be atomic transactions. Therefore, I feel that they also have a role to play for microservices and took the opportunity to write down some of my thoughts on the topic.

In one of my previous entries I may have inadvertently given the impression that in order to do microservices you need Linux containers, such as Docker. I want to clarify that so have written a new article which hopefully clarifies where those containers matter, especially in the Java world where we already have a container in the form of the JVM.

After writing my previous entry of how a container image, such as Docker, makes a natural unit of failure for an individual microservice or groups of related services, I wanted to follow up on one of the things I didn't get into detail on: state. Where does the state of the microservice reside? Is it within the container image, which may seem intuitively correct, or is it outside of the image? I've been thinking about state and replication for many years (well over 20) and was revisiting one of my earlier papers recently and got to thinking that it was relevant to microservices, or at least containers (since of course a container doesn't need to be tied to only being useful for microservices!) With that in mind, I found a few hours today to write up some thoughts on state and containers in general, but specifically microservices, Hopefully it makes some sense.

Another mini-vacation so another few hours to sit and write down some things that have been rumbling around in my head for a while. This time it's about Docker (container) images, microservices and how they can be combined to provide a natural unit of failure when building multi-service applications or composite services. Check it out on my personal blog, but hopefully the conclusion should be obvious:


"If you are building multiple microservices, or using them from other groups and organisations, within your applications or composite service(s), then do some thinking about how they are related and if they should fail as a unit then pull them together into a single image."

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