ellislofton / kube-crds-and-controllers

Kubernetes Controllers & CustomResourceDefinitions

The Goal

Watch all pods in the cluster and make sure they all have a configurable set of labels.

Dependencies

All the example controllers here use glide for dependency management. They are built based on client-go version v5.0.1 which is most compatible with Kubernetes v1.8.

If you want to use a newer version of client-go, you can find examples that use the latest client-go version, v6.0.0, with glide, godep, and dep in the deptoools folder.

All the controllers here should be able to work with client-go v6.0.0, but some code change would be required as client-go has made breaking changes between v5.0.x and v6.0.0.

Getting Ready

Before running any of the controllers below, make sure you everything is ready by running:

make

It may also be helpful to view the changes between controllers as a series of git commits. To do so you can run:

make diff-repo

And the repo will be generated, You can also find it at carsonoid/kube-crds-and-controllers-diffs

The Controllers

To illustrate basic functionality and common pitfalls the examples are broken up into three different groups: hard-coded, configmap-configued, and crd-configured. All the controllers do roughly the same thing but in different ways with different caveats.

controllers/hard-coded

A custom controller which has everything hard-coded

A simple hard-coded controller

A very simple controller which handles pod labels one at a time based on a hard-coded label map.

make run-controllers/hard-coded/simple

A structured hard-coded controller

The simple controller, but with configuration moved to a more defined structure. Suitable for loading from a file.

Hard-coded defaults via the struct:

make run-controllers/hard-coded/structured

Or via a config file:

make run-controllers/hard-coded/structured OPTS="-config controllers/hard-coded/config.yaml"

controllers/configmap-configured

Use a ConfigMap to configure the controller. This is essentially the same as passing a configmap based file into the pod. But with a reduced overhead and faster response to config changes.

Support for a single configuration in a configmap

Reads a configmap which supports a single configuration

make run-controllers/configmap-configured/single-config

Support for multiple configurations in a configmap

Reads a configmap which supports multiple configurations

make run-controllers/configmap-configured/multi-config

controllers/crd-configured

Use a CustomResourceDefinition to provide configurations to the controller. Using CRDs not only provides a very dynamic and Kubernetes native way of object handling, but it also provide instant usability by any existin Kubernetes tooling.

A blocking controller using CRDs

A controller which uses a CRDs to for all configuratins. Done with simple client-go mechanisms that are easy to understand but block during processing and can re-process the same resource multiple times

make run-controllers/crd-configured/simple

A controller that uses a workqueue to handle pods

A controller which uses CRDs for all configurations. But uses a workqueue to handle multiple resources at the same time. The workqueue is also a delta queue so multiple changes get combined into one processing run.

make run-controllers/crd-configured/workqueue