Simple event sourcing – users, authentication, authorization (part 6)

Previously we spend some time preparing the code to support multiple kinds of events and data, rather than just supporting blog posts. In this part we’ll add user accounts, together with the required authentication and authorization code. We’ll again use event sourcing and the memory image to keep track of all users and currently active sessions. But the biggest changes to the application are related to security, and authorization in particular. It turns out event sourcing allows for an additional layer of authorization which allows us to whitelist any change a particular user is allowed to make.
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How to use your happiness metric as a information radiator?

When I started recording the happiness of my team, I found it difficult to make this information transparent. I wanted to use it as a information radiator, so that everyone who looked at our Kanban or Scrum board could see (within 1 minute) how this particular team is doing, while on the other hand not all team members were confident enough to have their personal grade for all to see.
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Flowmulator – A Kanban flow simulator

UPDATE: Now you can add workers to a column and see if it helps getting work done faster. Try experimenting with the numbers and get the best configuration!

While reading blogs about Agile games, I came across this link of Karl Scotland.
Because I always like combining programming with building something that gets across Agile principles (our Battleship game is also a good example) this seemed like a good new project for our Fridays at Zilverline HQ. Bob Forma and me started this and within a few days we came up with this (You can check the source code here)

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Simple event sourcing – refactoring and transactions (part 5)

In the previous part we added blog post comment functionality. In this part we’ll do some refactoring and change the memory image implementation to automatically retry domain logic on optimistic locking conflicts, giving us a simplified form of transactions. We’ll also change the event store to support multiple types of event streams in a single event store.

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How to fill your happiness metric

Knowing how people think or feel about a certain subject can be very helpful in building trust, creating a team and to reveal impediments. Of course it can be very difficult to get team members to express their real opinions, especially when a team has just started. I think with patience and the right approach trust can (and will) be built and it will be easier to get real issues out in the open. The following practice can help you start this and make explicit what individual opinions in a team are.

I have used the following retrospective practice for several years now:

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Simple Event Sourcing – conflict resolution (part 4)

After our deep dive into a Redis event store implementation we’re now getting back to actually adding functionality to the blogging application. Like the Getting started with Rails guide we’ll add the capability to add comments to blog posts. Adding this functionality is straightforward, but it will require us to look into resolving conflicts when multiple people make modifications to the same blog post or comment concurrently.

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Simple event sourcing – Redis event store (part 3)

In the previous part we developed a fake event store for our blogging application. This event store just kept all events in-memory, making it unsuitable for production use. But it did allow us to adapt our application to using an event store, and let us work out the details of the event store interface without having to worry about an actual persistence mechanism.

In this part we’ll develop an event store implementation on top of Redis, a key-value store with support for additional data structures (such as lists and hashes), publish/subscribe, and transactions. If you’re more interested in adding new application functionality, you can safely skip this part and go to part 4 – conflict resolution.

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Simple event sourcing – consistency (part 2)

In the first part of this series we developed a simple blogging application that uses event sourcing to keep track of all changes made by the users. However, we did not yet write these events to durable storage. This means all data is lost when the application is restarted, which is clearly not acceptable. Saving and restoring events will be the responsibility of the event store, which we’ll start implementing in this part. But before we get to actually writing events to disk, we must first tackle the problem of maintaining data consistency when using event sourcing.

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Simple event sourcing – introduction (part 1)

This is the first part of a series on building an event sourced application. We’ll build a simple blogging application (inspired by the Ruby on RailsGetting Started” tutorial), so the domain should be familiar. This allows us to focus on implementing a memory image based architecture using event sourcing. Another goal is to show that this kind of architecture is not more complex (and arguably, simpler) than those implemented by traditional database centered applications. The example code is in Scala using the Play! web framework, but should be understandable enough if you come from a Java (or similar) background.
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Architect in Scrum

Last friday I gave a Masterclass called ‘Lean Agile Architecting’┬áto architects. Very interesting masterclass and a couple of things struck me. The issue for architects in an Agile environment is their position and responsibility.

The thing with the change from waterfall to agile is that architects feel their role is being undercut, the team just goes fast and are only paying attention to the Product Owner. The standard answer they seem to get is: ‘then join the team’, but they feel reluctant to do so, and most of the times they can not fully commit (full time). So they pass, and they feel miserable about it, since now this Agile project is going to make mistakes, and can not learn from past experiences and their expertise.

The answer lies in the closer observation of the definition of Agile and Architecture.
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