Updating ConfigMaps and propagation in Kubernetes - Commands & Configuration

Introduction

ConfigMaps store configuration data for your apps in Kubernetes. When you update a ConfigMap, your app needs to get the new data to work correctly without restarting everything manually.

When you want to change app settings without rebuilding the container image.

When you need to update environment variables for running pods.

When you want to apply new configuration to multiple pods at once.

When you want to avoid downtime by updating config without restarting pods manually.

When you want to test new configuration quickly in a live environment.

Config File - configmap.yaml

configmap.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: example-config
  namespace: default
data:
  app.properties: |
    log_level=info
    max_connections=100

This file creates a ConfigMap named example-config in the default namespace.

The data section holds configuration key-value pairs your app can use.

Commands

This command creates or updates the ConfigMap in Kubernetes with the settings from the file.

Terminal

kubectl apply -f configmap.yaml

Expected Output

configmap/example-config created

This command shows the current content of the ConfigMap to verify your changes.

Terminal

kubectl get configmap example-config -o yaml

Expected Output

apiVersion: v1

data:

  app.properties: |

    log_level=info

    max_connections=100

kind: ConfigMap

metadata:

  name: example-config

  namespace: default

  resourceVersion: "12345"

  uid: 123e4567-e89b-12d3-a456-426614174000

→

-o yaml - Outputs the ConfigMap in YAML format for easy reading

This command restarts the pods in the deployment so they load the updated ConfigMap.

Terminal

kubectl rollout restart deployment example-deployment

Expected Output

deployment.apps/example-deployment restarted

This command lists pods with the label app=example-app to check their status after restart.

Terminal

kubectl get pods -l app=example-app

Expected Output

NAME                                READY   STATUS    RESTARTS   AGE

example-deployment-5d8f7c9d7f-abc12 1/1     Running   0          10s

example-deployment-5d8f7c9d7f-def34 1/1     Running   0          10s

→

-l app=example-app - Filters pods by label to show only relevant pods

Key Concept

Updating a ConfigMap alone does not update running pods; you must restart pods or trigger a rollout to apply changes.

Common Mistakes

Updating the ConfigMap but not restarting pods or deployment.

Pods keep using old config because they load ConfigMaps only at start.

After updating the ConfigMap, run 'kubectl rollout restart deployment <deployment-name>' to reload config.

Editing ConfigMap with 'kubectl edit' but forgetting to save changes.

No changes are applied if edits are not saved properly.

Make sure to save and exit the editor to apply changes.

Assuming ConfigMap updates automatically propagate to pods without restart.

Kubernetes does not auto-update running pods with new ConfigMap data.

Manually restart pods or deployment to pick up new ConfigMap values.

Summary

Create or update ConfigMaps using 'kubectl apply -f configmap.yaml'.

Verify ConfigMap content with 'kubectl get configmap <name> -o yaml'.

Restart pods or deployment with 'kubectl rollout restart deployment <name>' to apply changes.

Check pod status with 'kubectl get pods' filtered by labels.