Context-specific K8s cluster and namespace

In the last post, I shared my context-specific direnv+asdf config for managing interpreters and tools. Since writing that, I attempted to add kubernetes contexts to the mix, and found only dubious advice from other folks advocating wrapper scripts and other oddities.

It’s poorly documented and somewhat counterintuitive, but kubectl supports multiple configuration files in the KUBECONFIG environment variable. Unlike most other unix-like applications however, it treats those configuration files almost exactly backwards – the first definition wins. But it’s enough to get the job done.

First, we create an overlay configuration file, with the minimum amount duplicated from ~/.kube/config.

Here’s the contents of ~/.kube/overlay/project-cluster-namespace. Name and path are completely arbitrary, but I do like to be organized.

contexts:
- context:
    cluster: gke_cluster_name
    namespace: my-application-namespace
    user: gke_authentication_bits
  name: my-favorite-context
current-context: my-favorite-context

From there, one need only add a KUBECONFIG environment variable to .envrc as follows:

export KUBECONFIG="${HOME}/.kube/overlay/project-cluster-namespace:${HOME}/.kube/config"

Entering the directory with direnv hooks active will yield the following:

direnv: loading ~/projects/my-application
direnv: export +KUBECONFIG

The result is a context-specific cluster and namespace without having to deal with clunky kubectl wrapper scripts or extra files in the workspace, and no side effects for other sessions.