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This is a talk by @timebertt at ContainerDays 2025 in Hamburg (event agenda).

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Do your Kubernetes controllers struggle to keep up with the demands of your growing infrastructure? As your clusters scale, traditional controller setups face increasing challenges, leading to slow reconciliation times, impacting application performance and overall cluster stability.

This session introduces sharding for Kubernetes controllers as a groundbreaking solution. By horizontally scaling controller workloads across multiple instances, it significantly improves scalability and addresses the inherent limitations of traditional leader election mechanisms.

In this session, we'll dive deep into the technical details of applying proven sharding mechanism from distributed databases to effectively partition controller workloads. We'll explore the underlying concepts and how to implement sharding in your own Kubernetes controllers.

Join us to learn how to overcome the scalability challenges of your Kubernetes controllers and unlock the full potential of your infrastructure.

While the operator pattern has revolutionized cloud-native applications, the current scalability constraints of Kubernetes controllers limit the full extent of large-scale implementations. This talk addresses this critical gap, introducing a project that enables horizontal scalability for Kubernetes controllers. With the presented concepts, the audience is empowered to scale their projects, services, and platforms with confidence. By showcasing practical solutions, the community is enabled to transcend the current limitations of controller-based systems. The talk is not just about the project itself; it’s about pushing the limits of scaling Kubernetes controllers and elevating the entire ecosystem of cloud-native platforms.

• https://github.com/timebertt/kubernetes-controller-sharding
• https://github.com/timebertt/masters-thesis-controller-sharding

Slides are built in Markdown using reveal.js, packaged with webpack, and deployed with Netlify.

Install a recent node version. Preferably, the one specified in .nvmrc (e.g., using nvm).

nvm use

Install the dependencies:

npm install

Perform a production build and serve the slides from the dist folder:

NODE_ENV=production npm run build
npm run serve

Important: Set NODE_ENV=production to yield the same build outputs as in production deploys to Netlify. If you don't set it, the QR will link to a local IP instead of the canonical URL, for example.

Run a dev server with hot-reload and open the slides in the browser:

npm start

Alternatively, use the preconfigured start run configuration for JetBrains IDEs.

Now, start editing the content files. When saving, slides are automatically rebuilt and refreshed in the browser.

Note, that npm start doesn't write the output to dist.

Run a full build and write output files to dist:

npm run build

Now, output files can be inspected in the dist folder. Also, the slides can be served locally from the dist folder (no hot-reload):

npm run serve

Using the above will output non-minimized files. Set NODE_ENV=production to enable minimization as it is done in Netlify builds:

NODE_ENV=production npm run build

Netlify builds and publishes new commits to the main branch on https://talk-controller-sharding.netlify.app/.

https://github.com/timebertt/talks contains a Netlify proxy configuration to make the slides available at https://talks.timebertt.dev/controller-sharding/.

The Netlify site is configured to publish deploy previews for pull requests to the main branch and for pushes to arbitrary other branches.