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Improving the Micronaut Guides Infrastructure

by Iván López Tags:

Since Micronaut 1.0, we have been heavily invested in the Micronaut Guides. We know they are a very good way to show different aspects of the framework with a working application that users can run and modify to their needs.

Over the last three years, we have published around 50 guides, most of them written in Java, Groovy, and Kotlin. We’ve put a lot of effort and time into keeping them updated to reflect the different Micronaut versions, but we’ve reached a point where keeping them up to date has become a huge task. Additionally, even if all the guides have tests, we didn’t run them unless we made some changes to the guide itself, so we were wasting a very good opportunity to have more tests for Micronaut itself and the different modules.

So we need another way …

A new infrastructure for the guides

We’ve created a new infrastructure for the guides with the following goals in mind:

  • Automatically migrate all the guides every time we release a new Micronaut version
  • Test the guides not only with the current Micronaut version, but also with the next Micronaut patch and minor snapshot versions
  • Keep all the guides in the same repository
  • Generate guides for Gradle and Maven users 
  • Simplify how we write the guides 

We have been working hard to create a new infrastructure for the guides with all those goals in mind. Let’s discuss how we’ve solved them in more detail.

Automatic migration of the guides

This is the most important thing we wanted to improve. Keeping the guides up to date with every Micronaut version is important because new users will find working examples with the latest version of the framework.

To fix this problem, we are leveraging Micronaut Launch. It’s not that we are calling the RESTful endpoints exposed by Launch, but that we are using the code that powers the website directly in our new guides. 

What we do is generate programmatically a project for the desired Micronaut version with every language combination, build tool, and the features needed for that guide. Then we copy specific code from the guide and package every project as a zip file ready for users to download. When a new Micronaut version is released, we only need to update the version in one file, submit a new pull request, and if all the tests pass, merge it, and we have automatically migrated all the guides to that version. Awesome, isn’t it? 🙂

Speaking about tests, how do we test the guides? 

During the guides generation process, we create on-the-fly the file build/code/ that contains the necessary code to execute either ./gradlew test or ./mvnw test in every generated guide.

Test Micronaut snapshot versions

We want to be able to detect potential issues with future Micronaut releases before it’s too late for us to fix them. We have set up a weekly cronjob in Github Actions that will run all the tests with the next Micronaut patch and minor snapshot versions. If something fails, we know that we have introduced an unnoticed regression or a breaking change that we need to avoid and fix it.

Use the same repository

With our current approach, every guide has its own repository; even when we have three language versions of a guide, we have three different repositories. Having every single guide in a different repository is not the best approach to keep things easy to maintain, either for us or for users willing to submit pull requests to improve the guides. 

Now every guide sits in a directory in the same repository, and inside it, we have the code for the three languages. This way, the text in the guides is the same, and if there is a typo, and we fix it, it’s fixed for all versions of the guide.

Guides for Gradle and Maven

We love Gradle, and we use it in every single Micronaut module, so it made sense to build our guides with Gradle. To be realistic, we know that a lot of our users prefer Maven, so we also want to generate guides using their favourite build tool to make things easier for them. Using Micronaut Launch infrastructure allows us to generate the same project with both Gradle and Maven in a very simple way. With this change, instead of creating three versions of each guide (one per language), we will have six (one per language and build tool). This makes it even more important to be able to generate new guides automatically and test them before new Micronaut releases.

Generating Maven projects for the guides has already paid the effort we’ve put into this. We’ve discovered and reported an issue in the Groovy compiler (that is fixed now) that only affects Maven users. To be fair, I personally don’t think that there will be any users out there using both Groovy and Maven, but you never know …

Simplify the process of writing guides

At this moment we create a table of content file, then include different Asciidoctor files and combine them all when rendering the guide. With this approach, we define the guide structure in a yaml file where we describe the name of the Asciidoctor files we use for the guides and the different titles for every section. Then the build process automatically processes that yaml file and generates a unique Asciidoctor file that is finally rendered as the HTML users can use. 

The problem is that it’s not straightforward to have a clear picture of the complete guide because all the text is scattered across different files. We also have some common text snippets that we use in all the guides, but those snippets live in another repository, so it makes it hard for us to maintain them and even harder for users to find them when they want to send improvements.

Now we write every guide as a single Asciidoctor file that include some text from common snippets that live in the same directory. This way we have a clear overview of the guide, and it’s easier to find those snippets and modify them when needed.

This unique Asciidoctor file per guide also needs to be language and build tool agnostic, meaning that the same source file needs to generate all six different combinations of guides. We have created custom kind-of Asciidoctor macros that help us include code snippets in the guides, make things easy to write, and make the guides agnostic to language and build tool. 

Here’s an example:

Imagine the Consul and Micronaut guide. This guide has three microservices, and it is written in the three languages (remember, in other guides and repositories). To include from the bookcatalogue microservice in the guide, we do:


What about the same file but from the bookrecommendation microservice?


And what about the same file but in the Groovy guide?


Can you spot the problems?

The first one is that to include the same class but from different languages, we need different Asciidoctor snippets. And even to include the same file but from different microservices, we also need to modify the path.

What about this?


We’ve written a custom macro that will expand the previous snippet into the right one taking care of the language and the application so it will generate any of the previously shown snippets appropriately for each case. We also have macros to include test files and resources and to define dependencies in a common way and render them differently for Gradle and Maven.

With this process, we generate the guide in two steps. In the first one we pre-process the guide Asciidoctor file to “expand” our own macros and resolve and include our common snippets. This generates a temporary Asciidoctor file that is rendered to get the final HTML of the guide.

Generating the guides locally

If you are interested in giving it a try locally, please clone this repository and run ./gradlew build to generate all the guides. You will find them in the build/dist directory.