Kubernetes MutableMap and ImmutableMap CRDs.

Overview

This repository implements an EXPERIMENTAL substitute for Kubernetes ConfigMaps. The idea behind these resources is to enable users to "freeze" their ConfigMap state at the point they create a Deployment, StatefulSet, Job, etc.

Trivia: These live under boos.mattmoor.io as I have named them after the ghosts in the Super Mario video game franchise that freeze when you are looking at them, but move when you look away.

Installation

You can install this via:

kubectl apply -f release.yaml

Lifecycle of a MutableMap

You create a MutableMap resource much like a ConfigMap, but with the content under spec: in place of data:

apiVersion: boos.mattmoor.io/v1alpha1
kind: MutableMap
metadata:
  name: my-config
spec:
  foo: bar

Each generation of a MutableMap will create an immutable snapshot of itself, e.g.

apiVersion: boos.mattmoor.io/v1alpha1
kind: ImmutableMap
metadata:
  name: my-config-00001
spec:
  foo: bar

Which in turn will stamp out ConfigMap resources, e.g.

apiVersion: v1
kind: ConfigMap
metadata:
  name: my-config-00001
data:
  foo: bar

The ImmutableMap disallows mutations via webhook, and the controller will revert any changes to the underlying ConfigMap as they are observed.

Using MutableMaps with resources containing a PodSpec

There are several ways that a PodSpec can reference a ConfigMap, e.g. a Kubernetes Deployment may project a particular key into an environment variable:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: example
spec:
  selector:
    matchLabels:
      app: example
  template:
    metadata:
      labels:
        app: example
    spec:
      containers:
      - name: example
        image: docker.io/mattmoor/something:interesting
        env:
        - name: BLAH
          valueFrom:
            configMapKeyRef:
              name: "foo"
              key: "bar"

The webhook this registers to aid with our own map types also registers to mutate the array of built-in Kubernetes types containing a PodSpec, so when applying the above if "foo" is actually a MutableMap with generation 36 what would actually be applied is:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: example
spec:
  selector:
    matchLabels:
      app: example
  template:
    metadata:
      labels:
        app: example
    spec:
      containers:
      - name: example
        image: docker.io/mattmoor/something:interesting
        env:
        - name: BLAH
          valueFrom:
            configMapKeyRef:
              name: "foo-00036"  # Updated to the frozen ConfigMap
              key: "bar"