Rancher Labs has been developing open source projects for about two years now. We have a ton of GitHub repositories under our hood, and our number keeps growing. The number of external contributions to our projects keeps growing, too; Rancher has become more well-known over the past year, and structural changes to our code base have made it easier to contribute. So what are these structural changes? I would highlight 3 major ones:
- Moving key Rancher features into separate microservices projects (Metadata, DNS, Rancher compose, etc.)
- Dockerizing microservices deployments
- Cataloging Dockerized application templates, and enabling them for deployment through the Rancher catalog
Item 2 acts as a bridge from 1 to 3. In this article, I will go over each item in more detail.
Moving key Rancher features to microservices
It is well-known that monolithic systems come with certain disadvantages:
- Their code bases are not easy to understand and modify
- Their features are hard to test in isolation
- They have longer test and release cycles.
But even if your code base is pluggable and well-structured, the last two challenges note above persist. Moving code into microservices helps to overcome these challenges, and creates a lower threshold for external committers: if you are new to open source development and willing to start contributing, smaller projects are simply easier to grasp. In addition, if you look at the project pull request history for Rancher External DNS, you might see something interesting: The majority of commits came from people with knowledge of different service providers. From a contributor’s point of view, having and bringing in specific service provider expertise reduces the pressure associated with making initial contributions to the project. And of course, the project benefits from getting all these provider extensions.
Let’s say as a contributor, you’ve created this new cool DNSimple provider plug-in. It was released with an external-dns service, and now you want to try it in Rancher. To adopt the changes, you don’t have to wait for the next Rancher release, nor do you have to change the Rancher code base. All you have to do is:
- fetch the last released image from the external-dns dockerhub repo
- create a docker-compose template with your service’s deployment details
- Register your image in Rancher catalog repo (more on how to deploy it from Rancher catalog, in the next section).
Deploying the service through Rancher catalog
At Rancher, we want to provide an easy way for users to describe and deploy their Docker-based applications. The Rancher catalog makes this possible. By selecting an entry from the catalog, and answering several questions, you can launch your service through the Rancher platform. All the services are grouped by category, so it is easy to search for a specific functionality:
Pick your newly added DNSimple service, fill in the fields and hit Launch: That’s it! Your service gets deployed in Rancher, and can be discovered and used by any other application. The catalog enables easy upgrades for microservices. Once the new service image is available and its template is published to the catalog, Rancher will get a notification, and your service can be upgraded to the latest version in a rolling fashion. The beauty of this is that you don’t have to update or upgrade Rancher when a new version of a microservice gets released. Besides providing a simple way of defining, deploying and upgrading microservices, the Rancher Catalog acts as a shared template library. If you are interested building an Elasticsearch microservice, using GlusterFS, or dockerizing DroneCI, check out their corresponding catalog items. And if you want to share your application, you can submit it to our Community catalog repo.
How microservices benefit Rancher as an orchestration platform
We’ve seen the single service implementation and deployment flow; let’s look at the bigger picture now. Any container orchestration platform should be easily extendable, especially when it comes to implementing a specific service provider extension. Building and deploying this extension shouldn’t be tightly coupled to the core platform, either. Moving out the code to its own microservice repo, dockerizing the service, and allowing it to deploy it using catalog, makes everything easier to maintain and support (as pictured below): We are planning to move the rest of Rancher’s key services to their own microservices. This will allow users to integrate the system service plugins of their choice with just a couple of clicks.
Learning from our community
Moving our key services – Metadata, Internal DNS – into dockerized microservices written in Go has helped with the release management, and driven more external commits. We’ve taken things one step further and developed an application catalog where users can share their applications’ templates in docker-compose format. This has taught us more about best DevOps best practices from within our community, made us more familiar with their use cases, and helped us improve our microservices implementations. Working on an open source project is always a two-way street – making your code easier to understand and manage helps the community contribute to and enhance the project. We have an awesome community, and appreciate every single contribution. We will continue improving contributors’ experience and learning from them. Alena Prokharchyk is a principal software engineer at Rancher Labs. If you have any questions or feedback, please contact me on twitter @lemonjet, or on GitHub (alena1108).