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configmap-watcher-example

This repo contains some examples of loading and watching Kubernetes configmaps. While most of the examples use the knative.dev/pkg/configmap package, which I found by chance and thought both useful and very straightforward (borderline insultingly easy) to use, the watch example just uses the vanilla client-go package. All code is free to borrow/steal/copy/do what you want with it.

There are four sample directories, each containing a different example:

  • load contains an example showing possibly the simplest method I've yet found for loading a configmap using the configmap.Load() method.
  • watch contains an example showing how to implement a simple and fairly robust watcher using client-go. This watcher has a default value to be used if the config map does not exist at startup or gets deleted later, and it automatically updates its information based on changes to the configmap (this is pretty much the point of using watchers).
  • kn-watch contains an example showing how to use knative's InformedWatcher to watch a configmap for changes and handle them dynamically.
  • watch-with-defaults contains an example showing how to use the same InformedWatcher type to both watch a configmap and to supply defaults in case the map cannot be loaded or is deleted while the application is running. This is basically a somewhat simpler version of my own watch implementation showing how you can reuse the knative package to simplify your code, if you like.

There is also a build script which will simply build four docker images, one for each example, and push them to the container registry specified by the REGISTRY environment variable. You must be logged into this registry for the script to succeed.

Last, in the configs directory there is a clusters.properties file you can use to create a configmap for trying out these examples, by running the command kubectl create cm clusters-config --from-env-file=clusters.properties. The examples are hardcoded to use clusters-config as the name of the configmap, just change that in the code and rebuild the docker images if you want to use a different name.