How to build an event store masterclass now available!

eventstore_960_520_darkerI’m happy to announce that “How to build an event store masterclass” is now available and open for enrollment. 

Take advantage of the huge benefits that CQRS and Event Sourced systems can bring. In this masterclass, you will learn the benefits of:

  • CQRS and why it is hugely beneficial in your software and especially for simplifying your designs to make it even easier to maintain software
  • Event Sourcing and its amazing opportunities it provides for the business / customers of your software
  • AWS managed services and how these services allow you to reap the benefits from the very beginning to achieve scalability, availability, reliability, and high performance
  • Simple but powerful architecture that I have used in my very own commercial projects with building AWS based cloud systems

Enroll now!

How to build an event store masterclass

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I’m close to finishing up my first masterclass about how to build an event store. If you are building CQRS, event sourced systems and with domain driven design (DDD) concepts, this class is for you. I’m planning on opening it up for enrollment to the general public within the next 2-3 weeks. Check out the details here.

Take advantage of the huge benefits that CQRS and Event Sourced systems can bring. In this masterclass, you will learn the benefits of:

  • CQRS and why it is hugely beneficial in your software and especially for simplifying your designs to make it even easier to maintain software
  • Event Sourcing and its amazing opportunities it provides for the business / customers of your software
  • AWS managed services and how these services allow you to reap the benefits from the very beginning to achieve scalability, availability, reliability, and high performance
  • Simple but powerful architecture that I have used in my very own commercial projects with building AWS based cloud systems

Enroll now!

Why you need serverless microservices, yesterday!

I have just published my FREE course: Why You Need Serverless Microservices, Yesterday“. Enroll for FREE!

WhyYouNeedServerlessMicroservices_960x520In this course I will walk you through the many benefits of creating serverless microservices instead of the traditional node / instance approach including the use of containers. There are more than enough things to worry about when you want to create a new cloud system or transform a legacy system to operate in the cloud.

From a business point of view, there are huge benefits in going serverless rather than instance based (including containers). A very large jump in business agility can be achieved through focusing on the problems and opportunities rather than the technical jungle of traditional computing solutions.

From a technical point of view, it is almost nirvana where you can eliminate many points of failures in the architecture.

Serverless Microservices Online Courses

Update 04/03/2019: I have completed the FREE course: “Why you need serverless microservices, yesterday!“. Enroll for FREE!
At the moment, I’m working on four online courses in the following order:

 

Why You Need Serverless Microservices, Yesterday, FREE Course

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In this course I will walk you through the many benefits of creating serverless microservices instead of the traditional node / instance approach including the use of containers. There are more than enough things to worry about when you want to create a new cloud system or transform a legacy system to operate in the cloud.

From a business point of view, there are huge benefits in going serverless rather than instance based (including containers). A very large jump in business agility can be achieved through focusing on the problems and opportunities rather than the technical jungle of traditional computing solutions.

From a technical point of view, it is almost nirvana where you can eliminate many points of failures in the architecture.

 

“How To Build An Event Store”, Paid Course

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Your event store is the heart of an event sourced system. The event store is the source of truth for all business events. It needs to be able capture and replay all domain events in your system reliably and with great performance.

In this course, I will walk you through building an event store that you can re-use in your own projects. In addition, I will walk you through building a read model that allows you to query domain events from the read model.

I will also go through why building your own event store has many more advantages over using a third-party event store.

We will be building the event store in AWS DynamoDB but you can apply the design to a traditional RDMS SQL storage just as well. I will go over the pros and cons in doing so.

 

“Architecting And Designing Event Based Microservices”, Paid Course

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Learn the details on how to design and architect event based microservices using Domain Driven Design (DDD), Event Storming, CQRS, and EventSourcing techniques. I will show you how best combine many principles, patterns, and techniques to create an architecture with as few points of failures as possible and still deliver a great solution.

What you will learn can be applied to cloud based systems but also to traditional, on-premise systems. The benefits are great in either environments.

Whether you are designing a new system in a greenfield environment or transforming a legacy system, I will show tips & tricks that you can use depending which type of project you are in.

 

“Implementing A Serverless Microservice in AWS”, Paid Course

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Learn the details on how to implement a serverless microservice in AWS using Domain Driven Design (DDD), CQRS, and EventSourcing techniques.

We will build a fully functioning billing system in AWS using Visual Studio and C# .NET Core. Even if you are not familiar with C# and .NET Core, you will learn a lot of practical tips on using the different AWS services including building fully automated CI/CD pipelines.

 

I’m still working on these courses but I’m planning on publishing “Why You Need Serverless Microservices, Yesterday” and “How To Build An Event Store” first.

My New YouTube Channel

I just created my new YouTube channel “Creating Great Software”. Have a look.

I will be publishing videos about creating great software including serverless computing in AWS. In addition, I will be publishing my STRONG opinions about the state of the software industry from time to time.

I’m super excited about this new channel and I’m looking forward in seeing your feedback. See you there!

Serverless System Course

In the past 27 professional years, I have been fortunate enough to gain a lot of experience and wisdom in 10 different software industries. These experiences are not just successful accomplishments but also plenty of failures and mistakes made along the way. It is ok to make mistakes as long as you learn from them, only then you will gain true wisdom in anything you do.

Over the years, I have always thought, “If I could gather a small team, I could share my knowledge and we can create great things“. Due to many circumstances, I never had the opportunity to mentor a small team and being in full control on what we would create. By full control I mean free from politics and other constraints. The sort of freedom you need to create and explore ideas without worrying about budgets, timelines, etc. When you can foster such an environment, great things get invented. Just look at the past successes in Silicon Valley.

How can I share my experiences and wisdom most efficiently and help you achieve your goals much more rapidly rather than doing it alone? I have decided it is time to create an online school where I can share all my knowledge and wisdom from the software industry. Well, how about an online course that is very deep in all aspects. An online course that would teach you the birds eye view of concepts and then drills down into the very deep aspects of it. A course that could show you actually how to put the conceptual components together in a very cohesive way. All the different pieces put together in an architecture that makes real sense and is practical and maintainable. We’ll leave the fluff out and concentrate on the entire system starting from a users perspective and walk backwards into the technical implementation details. In short, a

Serverless System Master Class

This master class would be extensive and we will go into a lot of details until we have built a working system that you could use in your future projects. As a minimum, you would learn a lot of concepts and software architecture. Since technology is always changing, I believe that the concepts will be more valuable then the implementation details in the course. In addition, how you bring these concepts together and why are extremely important because in your day-to-day work, you will have constraints that you need to work with and make compromises. There is no perfect architecture and even in this master class, you will touch on many different options one could take and why.

Please let me know if you are interested in the Serveless System Master Class. I would love to hear your feedback as I work on the course. I plan to post regular updates on my blog here.

Leave a comment below or contact me directly at thomasjaeger at gmail dot com and let me know your level of interest, please!

Event Store in AWS DynamoDB

Update 05/27/2019: How to build an event store masterclass” is now available. Learn how to build an event store using C#. NET Core, DynamoDB, MySQL for read models, and more.

In the past few weeks, I have been working on creating an event store in AWS DynamoDB and AWS S3. I use an event store for the domain driven design (DDD) concept in that system. Specifically, one of my systems uses CQRS and Event Sourcing (which is awesome, btw).

The idea for the event store started when I wanted to create my own event store for several reasons. I played with EventStore from Greg Young available at https://eventstore.org/ I encountered errors when I tested EventStore and I expected 100% functionality without issues. Besides, I did not want to babysit another persistence mechanism. I just do not have time for that.

I have created an event store before that was based entirely on Redis. That had worked great and it was super-fast. I used https://redislabs.com/ service to allow zero-maintenance of a fully clustered Redis solution. This has been working for some time now. The only problem was that it can have inconsistencies when it comes to running many applications nodes that use the Redis event store. Long story short, this has to do with complex timing, concurrency violations, etc.

So, I thought there must be a better way. I want zero administration headaches ideally, but I want to take advantage of the consistency capability of the underlying storage mechanism. I want the event store to be a service to the application itself that runs within the same process of the application. So, no need to babysit a separate event store cluster. I want the event store conceptually living side by side within the application.

If I can only take advantage of the consistency of the persistent mechanism, the application can then handle error conditions etc. accordingly based on what the use cases are.

After some experimenting and doing quiet a few load tests using http://loader.io, I can now say that the Event Store in DynamoDB has been born. My first 10,000 user / min load test has passed with flying colors and reached API response times of less than 10 ms with sustained rates of 170 clients / second. All this was running on a single cheap t2.medium instance. DynamoDB had to increase the throttling automatically to take this kind of load. This is one of those cool features, btw.

The event store I created in DynamoDB uses two concepts, Aggregates and Change Sets. Aggregates are the aggregates in your DDD system but only a handful of meta data. Change sets are one ore more domain events that are created when your DDD system processes a command.

I know I can get much higher numbers even by adding additional nodes and doing further tweaking. I would have to do much more load testing of course and tweaking but so far this has been a tremendous success and I’m super excited to take advantage of DynamoDB.

Anyways, I wanted to share this information. Maybe in the in future I can go into much more details. Time is the only problem I have really.

Creating IDs with CQRS and Event Sourcing in Java and .NET

I’m currently working on a cloud-based system that uses microservices with domain driven design and CQRS and Event Sourcing in Java. I love C# and .NET but I decided to do this in Java for several reasons. This could have been done in C# just as well. In fact, this system is a mix of some C# microservices and Java microservices. The important thing is that we are using the same concepts that are applicable when doing DDD and CQRS and Event Sourcing.

Anyways, I wanted to put down my thoughts on what I have been thinking about since last week and I hope this might be useful to anyone who came across the same question. So, my question since last week was this:

“Who creates an entity id in DDD when doing CQRS and Event Sourcing?”

Well, the way I have been doing this was as follows:

  1. When an application service executes a use case via one of its methods, it can create a new entity via a new immutable value object. All my entities’ ids are immutable value objects.
  2. Sometimes, a factory in the domain model creates new entities. Again, the entities’ ids are created via immutable value objects.
  3. Sometimes, a domain service creates new entities with immutable value objects.

This is all fine and good. I started to look at Greg Young‘s sample C# project at his Github here. For this who do not know him, he is a fantastic speaker and mentor for CQRS and Event Sourcing. Check out his videos, papers, and blog posts. Excellent material. He has a free 6 hour video here. And, while you are at it, check out his video about: “7 Reasons Why DDD Projects Fail“.

What poked my interest was this particular line in his CreateInventoryItem command code:

public class CreateInventoryItem : Command {
    public readonly Guid InventoryItemId;
    public readonly string Name;

    public CreateInventoryItem(Guid inventoryItemId, string name)
    {
        InventoryItemId = inventoryItemId;
        Name = name;
    }
}

If you look closely on line 5, you will see that the entity id inventoryItemId is being passed as part of the CreateInventoryItem command. This is a small but important detail.

I had an interesting thread discussion with Greg Young about this here. Greg raised a few good questions:

  1. What about when you want to send 3 commands?
  2. How will you start returning ids from commands?
  3. What if a command creates 3 entities?
  4. How will the domain get those ids back to the client?
  5. My UI is creating an account then the next step is managing some details. How does the UI go from one step to the next without knowing the account id?

As you can see, there are several good reasons why a client would want to create the ids instead of the domain model. Another reason I would want to add to this is that if the domain would create the ids, it would violate the goal of keeping track of all state changes in domain events with the commands as the initiators. In my opinion:

In a CQRS based system with Event Sourcing, commands carry all attributes that are required to execute the command including the creation of identities.

So, a client can create a command with ids that are based on Guids/Uuids and then send these creation commands with those ids. This allows you to do things such as persisting the commands and being able to replay those commands as well with 100% accuracy because the domain model with arrive every time to a deterministic state when you replay the domain events.

I like this very much and it provides a lot of freedom with inductive UIs / task based UIs.