Garbage Collection

When you use Kustomize’s configMapGenerator or secretGenerator, each modification produces a brand-new ConfigMap or Secret. Over time, this leads to multiple stale objects cluttering your cluster. This guide shows how to label and prune unused resources to keep your namespace clean.

The Problem: Stale ConfigMaps & Secrets

Run the following command to list all ConfigMaps:

kubectl get configmap

You might see output like this:

NAME                       DATA   AGE
db-cred-b6fhfd8c67         1      38h
db-cred-bf778fgm5h         1      2m13s
db-cred-mh7c9fbtfc         1      2m5s
kube-root-ca.crt           1      9d
redis-cred-229bkfk6cd      1      82s
redis-cred-b6fhfd8c67      1      38h
redis-cred-kh464kfbf2      1      118s

Here, you can spot three versions each of db-cred and redis-cred, but only the most recent ones are actually in use. The rest are stale leftovers.

Solution Overview: `kubectl apply --prune`

By adding a shared label to all generated ConfigMaps/Secrets and running kubectl apply --prune, Kubernetes will automatically delete any resource with that label that is no longer part of your current build.

Step 1: Add a Common Label

In your kustomization.yaml, include identical labels under options for each generator:

# kustomization.yaml
configMapGenerator:
  - name: db-cred
    literals:
      - password=password122
    options:
      labels:
        app-config: my-config
  - name: redis-cred
    literals:
      - password=password122
    options:
      labels:
        app-config: my-config

Step 2: Update Your Generator

When you change a literal—e.g., updating the password—keep the same label:

# kustomization.yaml (after update)
configMapGenerator:
  - name: db-cred
    literals:
      - password=password1224
    options:
      labels:
        app-config: my-config
  - name: redis-cred
    literals:
      - password=password1224
    options:
      labels:
        app-config: my-config

Step 3: Apply with Prune

Use the --prune flag along with -l to target your shared label:

kubectl apply -k k8s/overlays/prod/ --prune -l app-config=my-config

kubectl apply --prune will delete any resource in the namespace matching the label selector that isn’t in the current Kustomize output. Make sure only intended resources use this label.

Step 4: Verify Cleanup

After pruning, run:

kubectl get configmap

You should now see only the active ConfigMaps:

NAME                      DATA   AGE
db-cred-44h89htdm7        1      27m
kube-root-ca.crt          1      9d
redis-cred-c6k6d6bh64     1      2m7s

Quick Reference

Action	Command / Config Snippet
Label generators	`options.labels.app-config: my-config`
Apply with pruning	`kubectl apply -k <overlay> --prune -l app-config=my-config`
List ConfigMaps post-prune	`kubectl get configmap`

Introduction

Kustomize Overview

Kustomize Basics

Other Commands

Capstone Project

Secret Config Generator

Garbage Collection

The Problem: Stale ConfigMaps & Secrets

Solution Overview: `kubectl apply --prune`

Step 1: Add a Common Label

Step 2: Update Your Generator

Step 3: Apply with Prune

Step 4: Verify Cleanup

Quick Reference

Further Reading

Watch Video

Introduction

Kustomize Overview

Kustomize Basics

Other Commands

Capstone Project

Secret Config Generator

​The Problem: Stale ConfigMaps & Secrets

​Solution Overview: kubectl apply --prune

​Step 1: Add a Common Label

​Step 2: Update Your Generator

​Step 3: Apply with Prune

​Step 4: Verify Cleanup

​Quick Reference

​Further Reading

Watch Video

The Problem: Stale ConfigMaps & Secrets

Solution Overview: `kubectl apply --prune`

Step 1: Add a Common Label

Step 2: Update Your Generator

Step 3: Apply with Prune

Step 4: Verify Cleanup

Quick Reference

Further Reading