Creating ConfigMaps from files in Kubernetes - Step-by-Step CLI Walkthrough

Introduction

Sometimes your application needs configuration data like settings or keys. Kubernetes ConfigMaps let you store this data separately from your app code. Creating ConfigMaps from files helps you keep configuration organized and easy to update.

When you want to provide environment-specific settings to your app without changing the app itself

When you have multiple configuration files that your app needs to read

When you want to update configuration without rebuilding your container image

When you want to share configuration data across multiple pods

When you want to keep sensitive data separate from your app code (non-secret data)

Commands

This command creates a ConfigMap named 'my-config' using the contents of the file 'app.properties'. Kubernetes stores the file content as key-value pairs inside the ConfigMap.

Terminal

kubectl create configmap my-config --from-file=app.properties

Expected Output

configmap/my-config created

→

--from-file - Specifies the file to use as the source for the ConfigMap data

This command shows the details of the ConfigMap 'my-config' in YAML format so you can verify the data was stored correctly.

Terminal

kubectl get configmaps my-config -o yaml

Expected Output

apiVersion: v1

kind: ConfigMap

metadata:

  name: my-config

data:

  app.properties: |

    # content of app.properties file here

    key1=value1

    key2=value2

→

-o yaml - Outputs the ConfigMap details in YAML format

This command creates a ConfigMap named 'multi-config' from two files, 'config1.txt' and 'config2.txt'. Each file's content is stored under its filename as a key.

Terminal

kubectl create configmap multi-config --from-file=config1.txt --from-file=config2.txt

Expected Output

configmap/multi-config created

→

--from-file - Can be used multiple times to add multiple files to the ConfigMap

This command shows a summary of the 'multi-config' ConfigMap, including the keys (filenames) it contains and their sizes.

Terminal

kubectl describe configmap multi-config

Expected Output

Name:         multi-config

Namespace:    default

Labels:       <none>

Annotations:  <none>

Data

====

config1.txt:

  25 bytes

config2.txt:

  30 bytes

Events:       <none>

Key Concept

If you remember nothing else from this pattern, remember: ConfigMaps let you store configuration data from files so your app can use it without changing the app image.

Common Mistakes

Using a directory path instead of a file path with --from-file

The command expects a file, not a directory, so it will fail or create an empty ConfigMap

Specify the exact file path for each --from-file flag

Not verifying the ConfigMap content after creation

You might think the ConfigMap has the right data but it could be empty or incorrect

Always run 'kubectl get configmaps NAME -o yaml' or 'kubectl describe configmap NAME' to check

Using the same filename multiple times with --from-file

Keys in ConfigMaps must be unique; duplicate filenames will overwrite previous data silently

Ensure each file has a unique name or use --from-file=key=filepath to set custom keys

Summary

Use 'kubectl create configmap NAME --from-file=filename' to create a ConfigMap from a file.

Verify the ConfigMap content with 'kubectl get configmaps NAME -o yaml' or 'kubectl describe configmap NAME'.

You can add multiple files by repeating the --from-file flag for each file.