configuration

DRY is an important principle in software development. This post will show you how to apply it to Apache APISIX configuration. The DRY principle 'Don’t repeat yourself' (DRY) is a principle of software development aimed at reducing repetition of information which is likely to change, replacing it with abstractions that are less likely to change, or using data normalization which avoids redundancy in the first place.

I’m in the process of adding more components to my OpenTelemetry demo (again!). The new design deploys several warehouse services behind the inventory service so the latter can query the former for data via their respective HTTP interface. I implemented each warehouse on top of a different technology stack. This way, I can show OpenTelemetry traces across several stacks.

Two weeks ago, I wrote how you could write a Spring application with no annotations. Many alternatives are available to configure your Spring app. I’d like to list them in this post, leaving Spring Boot out of the picture on purpose. Core concepts Property file XML Groovy DSL Self-annotated classes Configuration classes Kotlin DSL Bean definitions Beans Conclusion Core concepts A couple of concepts are central in Spring.

When I started my career, XML was ubiquitous. The meta-information in a Java JAR file - the manifest - follows a proprietary format. But Java EE designers built it from the ground up on XML: meta-information of all artifacts is in XML format e.g. web.xml, ejb-jar.xml, application.xml, etc. Java EE is one example I experienced personally. But XML was everywhere in the enterprise world at the time. Its prevalence manifested itself in two areas: configuration and data transfer.

There are a lot of different ways to configure containers running on Kubernetes: Environment variablesConfig mapsVolumes shared across multiple podsArguments passed to scheduled podsetc. Those alternatives fit a specific context, with specific requirements. For example, none of them allow you to clone a Git repository before the container starts. It would be possible to design that feature into the image itself.

Every now and then, there’s an angry post or comment bitching about how the Spring framework is full of XML, how terrible and verbose it is, and how the author would never use it because of that. Of course, that is completely crap. First, when Spring was created, XML was pretty hot. J2EE deployment descriptors (yes, that was the name at the time) was XML-based. Anyway, it’s 2017 folks, and there are multiple ways to skin a cat.

Deploying on different environments requires configuration, e.g. database URL(s) must be set on each dedicated environment. In most - if not all Java applications, this is achieved through a .properties file, loaded through the appropriately-named Properties class. During development, there’s no reason not to use the same configuration system, e.g. to use an embedded h2 database instead of the production one.

Integration Testing Spring applications mandates to create small dedicated configuration fragments and to assemble them either during normal run of the application or during tests. Even in the latter case, different fragments can be assembled in different tests. However, this practice doesn’t handle the use-case where I want to use the application in two different environments.