How to Write a Kubernetes Operator

The previous post explained what a Kubernetes Operator is: a controller that watches a custom resource and continuously reconciles the actual cluster state toward the desired state. That explanation is useful. This one is different. This one ends with a working Operator. We're going to build one end-to-end: define a custom resource, write the reconciliation logic in Go, see the equivalent in Java, wire up the RBAC, and deploy it to a cluster.… Read More

Explained: Kubernetes Operators

You're deploying Kafka to Kubernetes. You write a Deployment for the brokers, a StatefulSet for ZooKeeper, ConfigMap s for configuration, Services to expose everything, and a handful of PersistentVolumeClaim s for storage. The cluster comes up. Then a broker dies and Kubernetes restarts it, but it comes back with the wrong broker ID and can't rejoin the cluster. Kubernetes did what it was told: restart the container. But it had no idea wha… Read More

Explained: Cookie Consent

You land on a news site to read one article. Before you can see a single word of it, a banner fills half the screen. "We value your privacy." There are three buttons: Accept All, Manage Preferences, and something like "Continue without accepting" that's grey and tiny and hard to find. You click Accept All because you just want to read the article. This happens roughly a dozen times a day for most people using the web. Most… Read More

Explained: CoreDNS

You deploy a new service to your Kubernetes cluster. The pods come up healthy. You open a shell inside one of them and try to reach another service by name — http://payments-service — and nothing happens. Timeout. You try the full name: http://payments-service.billing.svc.cluster.local . Still nothing. You try the service's ClusterIP directly, and it works fine. Something in the cluster is resolving names, but it's not resolving yours. If … Read More