Using ConfigMaps as environment variables in Kubernetes - Commands & Configuration

Introduction

Sometimes your applications need settings that can change without rebuilding the app. ConfigMaps let you store these settings separately and use them as environment variables inside your containers.

When you want to change app settings like API URLs without changing the app code.

When multiple pods need the same configuration values and you want to manage them in one place.

When you want to keep sensitive or environment-specific data outside your container images.

When you want to update configuration without restarting or rebuilding your containers manually.

When you want to separate configuration from code for easier maintenance and updates.

Config File - configmap-env.yaml

configmap-env.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: my-app-config
data:
  APP_MODE: production
  LOG_LEVEL: info
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app
spec:
  replicas: 1
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      labels:
        app: my-app
    spec:
      containers:
      - name: my-app-container
        image: nginx:1.23.3
        envFrom:
        - configMapRef:
            name: my-app-config

This file has two parts separated by ---:

• ConfigMap: Stores key-value pairs like APP_MODE and LOG_LEVEL.
• Deployment: Runs a pod with one container using the nginx image.
• The envFrom section tells Kubernetes to load all keys from the ConfigMap as environment variables inside the container.

Commands

This command creates the ConfigMap and the Deployment in your Kubernetes cluster. It sets up the environment variables for the app container.

Terminal

kubectl apply -f configmap-env.yaml

Expected Output

configmap/my-app-config created

deployment.apps/my-app created

Check that the pod from the Deployment is running and ready.

Terminal

kubectl get pods

Expected Output

NAME                      READY   STATUS    RESTARTS   AGE

my-app-6d4b7f7d7f-abcde  1/1     Running   0          10s

Inside the running pod, print the value of the APP_MODE environment variable to verify it was set from the ConfigMap.

Terminal

kubectl exec my-app-6d4b7f7d7f-abcde -- printenv APP_MODE

Expected Output

production

Check the LOG_LEVEL environment variable inside the pod to confirm it matches the ConfigMap value.

Terminal

kubectl exec my-app-6d4b7f7d7f-abcde -- printenv LOG_LEVEL

Expected Output

info

Key Concept

If you remember nothing else from this pattern, remember: ConfigMaps let you inject configuration data as environment variables into your containers without changing the container image.

Common Mistakes

Not referencing the ConfigMap name correctly in the Deployment's envFrom section.

The container won't receive the environment variables if the ConfigMap name is wrong or missing.

Ensure the configMapRef name exactly matches the ConfigMap metadata name.

Trying to use env instead of envFrom for many variables, writing each key manually.

This is error-prone and harder to maintain when you have many variables.

Use envFrom with configMapRef to load all keys at once.

Changing the ConfigMap after pod creation without restarting the pod.

Pods do not automatically reload environment variables from updated ConfigMaps.

After updating the ConfigMap, restart the pod to apply new environment variables.

Summary

Create a ConfigMap with key-value pairs for your app settings.

Reference the ConfigMap in your Deployment using envFrom to load all keys as environment variables.

Verify the pod is running and check environment variables inside the container with kubectl exec.

Practice

1. What is the main purpose of using a ConfigMap in Kubernetes when setting environment variables for a pod?

easy

A. To separate configuration data from application code for easier updates

B. To store container images for pods

C. To manage network policies between pods

D. To define resource limits for containers

Solution

1. Step 1: Understand ConfigMap role

   ConfigMaps hold configuration data separately from app code, allowing updates without rebuilding images.

2. Step 2: Identify correct purpose

   Among options, only separating config data matches ConfigMap's main use for environment variables.

3. Final Answer:

   To separate configuration data from application code for easier updates -> Option A

4. Quick Check:

   ConfigMap purpose = separate config data [OK]

Hint: ConfigMaps separate config from code for flexible env vars [OK]

Common Mistakes:

• Confusing ConfigMaps with container images
• Thinking ConfigMaps manage network or resources
• Using ConfigMaps to store secrets (use Secrets instead)

2. Which of the following is the correct syntax to load all keys from a ConfigMap named app-config as environment variables in a pod spec?

easy

A. envFrom:
- configMapRef:
name: app-config

B. env:
- name: app-config
valueFrom:
configMapKeyRef:
name: app-config

C. configMap:
name: app-config

D. envFrom:
- secretRef:
name: app-config

Solution

1. Step 1: Identify correct envFrom usage

   To load all keys as env vars, use envFrom with configMapRef and the ConfigMap name.

2. Step 2: Check options for syntax correctness

   envFrom: - configMapRef: name: app-config correctly uses envFrom with configMapRef. Others misuse keys or use secretRef incorrectly.

3. Final Answer:

   envFrom: - configMapRef: name: app-config -> Option A

4. Quick Check:

   Use envFrom + configMapRef for all keys [OK]

Hint: Use envFrom with configMapRef to load all keys [OK]

Common Mistakes:

• Using env instead of envFrom for all keys
• Confusing configMapRef with secretRef
• Missing indentation or wrong key names

3. Given this pod spec snippet, what environment variables will be available inside the container?

envFrom:
  - configMapRef:
      name: my-config

And the ConfigMap my-config contains keys: API_URL=https://api.example.com and TIMEOUT=30.

medium

A. Only API_URL=https://api.example.com

B. API_URL=https://api.example.com and TIMEOUT=30

C. Only TIMEOUT=30

D. No environment variables will be set

Solution

1. Step 1: Understand envFrom with configMapRef

   Using envFrom with configMapRef loads all keys from the ConfigMap as environment variables.

2. Step 2: Check ConfigMap keys

   The ConfigMap has two keys: API_URL and TIMEOUT, so both become env vars.

3. Final Answer:

   API_URL=https://api.example.com and TIMEOUT=30 -> Option B

4. Quick Check:

   envFrom loads all keys as env vars [OK]

Hint: envFrom loads all ConfigMap keys as env vars [OK]

Common Mistakes:

• Assuming only one key loads at a time
• Confusing envFrom with env and missing keys
• Thinking ConfigMap keys are not environment variables

4. You applied this pod spec to use a ConfigMap as environment variables, but the container does not see the variables. What is wrong?

envFrom:
  - configMapRef:
      name: wrong-config-name

The ConfigMap you created is named app-config.

medium

A. The pod spec must use secretRef instead of configMapRef

B. envFrom cannot be used to load ConfigMaps

C. ConfigMaps cannot be used as environment variables

D. The ConfigMap name in the pod spec does not match the actual ConfigMap name

Solution

1. Step 1: Compare ConfigMap names

   The pod spec references wrong-config-name, but the actual ConfigMap is app-config.

2. Step 2: Understand impact of name mismatch

   If names don't match, Kubernetes cannot find the ConfigMap, so env vars won't be set.

3. Final Answer:

   The ConfigMap name in the pod spec does not match the actual ConfigMap name -> Option D

4. Quick Check:

   ConfigMap name must match exactly [OK]

Hint: Check ConfigMap name spelling matches pod spec [OK]

Common Mistakes:

• Using secretRef instead of configMapRef incorrectly
• Assuming envFrom can't load ConfigMaps
• Ignoring case sensitivity in names

5. You want to update environment variables in a running pod without rebuilding the container image. Which approach using ConfigMaps is correct?

hard

A. Use a Secret instead of ConfigMap for environment variables

B. Modify the container image to include new environment variables

C. Create or update a ConfigMap and reference it with envFrom in the pod spec, then restart the pod

D. Edit the pod spec to add environment variables directly and redeploy the image

Solution

1. Step 1: Understand ConfigMap update workflow

   ConfigMaps allow updating config data separately; updating the ConfigMap and restarting the pod applies new env vars without rebuilding images.

2. Step 2: Evaluate options for best practice

   Create or update a ConfigMap and reference it with envFrom in the pod spec, then restart the pod correctly uses ConfigMap with envFrom and pod restart. Others require image rebuild or confuse Secrets with ConfigMaps.

3. Final Answer:

   Create or update a ConfigMap and reference it with envFrom in the pod spec, then restart the pod -> Option C

4. Quick Check:

   Update ConfigMap + restart pod for new env vars [OK]

Hint: Update ConfigMap and restart pod, no image rebuild needed [OK]

Common Mistakes:

• Rebuilding container image unnecessarily
• Confusing Secrets with ConfigMaps for non-sensitive data
• Editing pod spec without restarting pod