Using ConfigMaps as mounted volumes in Kubernetes - Mini Project: Build & Apply

Using ConfigMaps as mounted volumes

📖 Scenario: You are managing a Kubernetes application that needs configuration files to be available inside its containers. Instead of baking these configs into the container image, you want to use Kubernetes ConfigMaps to provide these files dynamically.This approach helps you update configuration without rebuilding images, similar to how you might keep your app settings in a separate folder on your computer that your app reads from.

🎯 Goal: Learn how to create a ConfigMap with configuration data, mount it as a volume inside a Pod, and verify the configuration files are accessible inside the container.

📋 What You'll Learn

Create a ConfigMap named app-config with two configuration files: app.properties and db.properties with exact content.

Create a Pod named configmap-pod that mounts the app-config ConfigMap as a volume at /etc/config.

Verify the mounted files inside the Pod by printing their contents.

💡 Why This Matters

🌍 Real World

Using ConfigMaps as mounted volumes is a common way to provide configuration files to applications running in Kubernetes without rebuilding container images.

💼 Career

Understanding ConfigMaps and volume mounts is essential for Kubernetes administrators and DevOps engineers to manage application configurations efficiently.

1

Create a ConfigMap with configuration files

Create a ConfigMap named app-config with two files: app.properties containing app.name=MyApp and app.version=1.0, and db.properties containing db.host=localhost and db.port=5432. Use the kubectl create configmap app-config --from-literal=app.properties='app.name=MyApp\napp.version=1.0' --from-literal=db.properties='db.host=localhost\ndb.port=5432' command.

Kubernetes

# Create the ConfigMap named app-config with the specified files
# Your code here

Hint

Use kubectl create configmap with --from-literal twice to add two files.

2

Create a Pod that mounts the ConfigMap as a volume

Create a Pod manifest named configmap-pod.yaml with a Pod named configmap-pod. The Pod should run the busybox image and mount the app-config ConfigMap as a volume named config-volume at the path /etc/config. Use the command: ['sleep', '3600'] to keep the Pod running.

Kubernetes

kubectl create configmap app-config --from-literal=app.properties='app.name=MyApp\napp.version=1.0' --from-literal=db.properties='db.host=localhost\ndb.port=5432'

# Create a Pod manifest named configmap-pod.yaml with the specified volume mount
# Your code here

Hint

Define a Pod with a container that mounts the ConfigMap as a volume at /etc/config.

3

Apply the Pod manifest and verify the Pod is running

Apply the Pod manifest file configmap-pod.yaml using kubectl apply -f configmap-pod.yaml. Then check the Pod status with kubectl get pod configmap-pod to confirm it is running.

Kubernetes

kubectl create configmap app-config --from-literal=app.properties='app.name=MyApp\napp.version=1.0' --from-literal=db.properties='db.host=localhost\ndb.port=5432'

apiVersion: v1
kind: Pod
metadata:
  name: configmap-pod
spec:
  containers:
  - name: busybox
    image: busybox
    command: ['sleep', '3600']
    volumeMounts:
    - name: config-volume
      mountPath: /etc/config
  volumes:
  - name: config-volume
    configMap:
      name: app-config

# Apply the Pod manifest and check Pod status
# Your code here

Hint

Use kubectl apply -f to create the Pod and kubectl get pod to check its status.

4

Verify the ConfigMap files inside the Pod

Use kubectl exec configmap-pod -- cat /etc/config/app.properties and kubectl exec configmap-pod -- cat /etc/config/db.properties to print the contents of the mounted ConfigMap files inside the Pod.

Kubernetes

kubectl create configmap app-config --from-literal=app.properties='app.name=MyApp\napp.version=1.0' --from-literal=db.properties='db.host=localhost\ndb.port=5432'

apiVersion: v1
kind: Pod
metadata:
  name: configmap-pod
spec:
  containers:
  - name: busybox
    image: busybox
    command: ['sleep', '3600']
    volumeMounts:
    - name: config-volume
      mountPath: /etc/config
  volumes:
  - name: config-volume
    configMap:
      name: app-config

kubectl apply -f configmap-pod.yaml
kubectl get pod configmap-pod

# Print the contents of /etc/config/app.properties and /etc/config/db.properties inside the Pod
# Your code here

Hint

Use kubectl exec with cat to read the files inside the Pod.

Practice

1. What is the main purpose of using a ConfigMap as a mounted volume in Kubernetes?

easy

A. To provide configuration data as files inside a container without rebuilding the image

B. To store container logs persistently

C. To increase container CPU limits dynamically

D. To manage container networking settings

Solution

1. Step 1: Understand ConfigMap role

   ConfigMaps hold configuration data separately from container images.

2. Step 2: Understand mounting as volume

   Mounting a ConfigMap as a volume makes its data available as files inside the container.

3. Final Answer:

   To provide configuration data as files inside a container without rebuilding the image -> Option A

4. Quick Check:

   ConfigMap volume = config files inside container [OK]

Hint: ConfigMaps as volumes = config files inside container [OK]

Common Mistakes:

• Confusing ConfigMaps with persistent storage for logs
• Thinking ConfigMaps control CPU or networking
• Assuming ConfigMaps require container rebuild

2. Which of the following is the correct YAML snippet to mount a ConfigMap named app-config as a volume in a pod?

easy

A. volumes:\n - name: config-volume\n emptyDir: {}

B. volumes:\n - name: config-volume\n secret:\n name: app-config

C. volumes:\n - name: config-volume\n persistentVolumeClaim:\n claimName: app-config

D. volumes:\n - name: config-volume\n configMap:\n name: app-config

Solution

1. Step 1: Identify volume type for ConfigMap

   ConfigMaps are mounted using the configMap field inside volumes.

2. Step 2: Match correct YAML structure

   volumes:\n - name: config-volume\n configMap:\n name: app-config correctly uses configMap: with the ConfigMap name.

3. Final Answer:

   volumes:\n - name: config-volume\n configMap:\n name: app-config -> Option D

4. Quick Check:

   ConfigMap volume uses configMap: name [OK]

Hint: ConfigMap volume uses 'configMap:' with name [OK]

Common Mistakes:

• Using secret instead of configMap for ConfigMap volumes
• Confusing persistentVolumeClaim with ConfigMap
• Using emptyDir which is an empty temp volume

3. Given this pod volume mount snippet, what file content will appear inside the container at /etc/config/app.properties if the ConfigMap app-config has a key app.properties with value mode=production?

volumes:
  - name: config-volume
    configMap:
      name: app-config
containers:
  - name: app
    image: myapp
    volumeMounts:
      - name: config-volume
        mountPath: /etc/config
        readOnly: true

medium

A. A directory named app.properties with no content

B. No file created because mountPath is a directory

C. A file named app.properties with content 'mode=production'

D. A file named app.properties with content 'mode=development'

Solution

1. Step 1: Understand ConfigMap key to file mapping

   Each key in ConfigMap becomes a file with that name and its value as content.

2. Step 2: Check mountPath and file presence

   Mounting at /etc/config creates files inside that directory, including app.properties with content mode=production.

3. Final Answer:

   A file named app.properties with content 'mode=production' -> Option C

4. Quick Check:

   ConfigMap key = filename, value = file content [OK]

Hint: ConfigMap keys become files with their values inside mountPath [OK]

Common Mistakes:

• Thinking mountPath must be a file, not directory
• Assuming file content changes without ConfigMap update
• Confusing file name with directory

4. You mounted a ConfigMap as a volume, but inside the container the files are missing. Which is the most likely cause?

medium

A. The ConfigMap name in the volume spec does not match any existing ConfigMap

B. The container image does not support volumes

C. The pod has no CPU resources assigned

D. The ConfigMap keys are empty strings

Solution

1. Step 1: Check ConfigMap reference correctness

   If the ConfigMap name in the volume spec is wrong, Kubernetes cannot mount it, so files won't appear.

2. Step 2: Eliminate unrelated causes

   Container images support volumes by default; CPU resources don't affect file mounting; keys cannot be empty strings in ConfigMaps.

3. Final Answer:

   The ConfigMap name in the volume spec does not match any existing ConfigMap -> Option A

4. Quick Check:

   Wrong ConfigMap name = no files mounted [OK]

Hint: Check ConfigMap name spelling in volume spec [OK]

Common Mistakes:

• Blaming container image for missing files
• Ignoring ConfigMap existence or name mismatch
• Assuming resource limits affect volume mounts

5. You want to mount only specific keys from a ConfigMap named app-config as files inside a container at /etc/config. Which volume configuration snippet achieves this?

hard

A. volumes:
- name: config-volume
configMap:
name: app-config
exclude:
- unused_key

B. volumes:
- name: config-volume
configMap:
name: app-config
items:
- key: database_url
path: db_url
- key: log_level
path: log_level

C. volumes:
- name: config-volume
secret:
name: app-config
items:
- key: database_url
path: db_url

D. volumes:
- name: config-volume
configMap:
name: app-config
keys:
- database_url
- log_level

Solution

1. Step 1: Understand selective key mounting

   Kubernetes allows selecting specific keys from a ConfigMap using the items field with key and path.

2. Step 2: Identify correct syntax

   volumes: - name: config-volume configMap: name: app-config items: - key: database_url path: db_url - key: log_level path: log_level correctly uses items with key-path pairs to mount only chosen keys as files.

3. Final Answer:

   volumes: - name: config-volume configMap: name: app-config items: - key: database_url path: db_url - key: log_level path: log_level -> Option B

4. Quick Check:

   Use items with key and path to select keys [OK]

Hint: Use 'items' with key and path to mount specific keys [OK]

Common Mistakes:

• Using 'keys' instead of 'items' for selection
• Confusing ConfigMap with Secret for this purpose
• Trying to exclude keys instead of selecting them