architecture

Following on from my previous post about not having too much configuration, I want to talk about how I design software. I try and follow what I call “outside in design”; I try and make something that requires the bare minimum amount of configuration to cover the most common of use-cases. Once this functionality is working, further configuration can be added to cover the next most common use cases. API Reduction As A Feature The first example I want to go through is how I removed options from an HTTP rate limiter we use....

One of the many reasons given for using microservices rather than a mono repository is that it enforces boundaries between services/modules. However, there are ways to achieve strong boundaries between modules/services in one repository, using tools which are already available: test runners. Given a repository with the following structure: . ├── libraries │ ├── core │ ├── events │ └── ui ├── services │ ├── catalogue │ ├── billing │ └── shipping └── tools └── admin-cli There are a few rules we should enforce:...

I haven’t seen Expand-Contract written about in some years, and I think it is a great way of performing database schema migrations without the need for application downtime. I also realised that it also applies to microservices and service-to-service communication in general. The Easy Example One of the two examples given is wanting to change how an address is stored in a database. The schema starts off looking like this:...

An interesting question came up at work today: how do you tag your Docker images? In previous projects, I’ve always used a short git sha, or sometimes a semver, but with no great consistency. As luck would have it, I had pushed for a change in tagging format at a client not so long ago as the method we were using didn’t make a lot of sense and, worst of all, it was a manual process....

This is a text version of a short talk (affectionately known as a “Coffee Bag”) I gave at work this week, on Architecture Design Records. You can see the slides here, but there isn’t a recording available, unfortunately. It should be noted; these are not to replace full architecture diagrams; you should definitely still write C4 Models to cover the overall architecture. ADRs are for the details, such as serializer formats, convention-over-configuration details, number precisions for timings, or which metrics library is used and why....

One of the reasons people list for using MicroServices is that it helps enforce separation of concerns. This is usually achieved by adding a network boundary between the services. While this is useful, it’s not without costs; namely that you’ve added a set of new failure modes: the network. We can achieve the same separation of concerns within the same codebase if we put our minds to it. In fact, this is what Simon Brown calls a Modular Monolith, and DHH calls the Majestic Monolith....

Feature Toggles are a great way of helping to deliver working software, although there are a few things which could go wrong. See my talk Feature Toggles: The Good, The Bad and The Ugly for some interesting stories and insights on it! I was talking with a colleague the other day about how you could go about implementing Feature Toggles in a centralised manner into an existing system, preferably with a little overhead as possible....

Having recently finished reading the Building Evolutionary Architectures: Support Constant Change book, I got to thinking about a system which was fairly representative of an architecture which was fine for it’s initial version, but it’s usage had outgrown the architecture. Example System: Document Storage The system in question was a file store for a multi user, internal, desktop based CRM system. The number of users was very small, and the first implementation was just a network file share....

It’s no secret I am a fan of strong typing - not only do I talk and blog about it a lot, but I also have a library called Stronk which provides strong typed configuration for non dotnet core projects. The problem I come across often is large configurations. For example, given the following project structure (3 applications, all reference the Domain project): DemoService `-- src |-- Domain | |-- Domain....

TLDR: I still don’t like Repositories! Recently I had a discussion with a commenter on my The problems with, and solutions to Repositories post, and felt it was worth expanding on how I don’t use repositories. My applications tend to use the mediator pattern to keep things decoupled (using the Mediatr library), and this means that I end up with “handler” classes which process messages; they load something from storage, call domain methods, and then write it back to storage, possibly returning some or all the data....