Kubernetes Environment Variables

How to inject configuration into Kubernetes containers — from literal values to ConfigMap and Secret references. Synthesized from CKA Day 11 — Multi Container Pod Kubernetes: Sidecar vs Init Container.

Why Environment Variables?

Environment variables are the twelve-factor app standard for configuration. In Kubernetes, they allow you to:

• Keep images environment-agnostic (same image for dev/staging/prod)
• Inject dynamic values (Pod IP, node name, namespace)
• Reference centralized configuration stored in ConfigMaps and Secrets
• Pass sensitive data without baking it into container images

Security note: Environment variables are visible in kubectl describe pod, docker inspect, and /proc/<pid>/environ. For highly sensitive secrets, consider using a secrets manager sidecar or volume-mounted secret files instead of env vars. Source: CKA Day 11

Literal Values

The simplest form — hardcoded in the Pod spec:

spec:
  containers:
  - name: my-app
    image: nginx
    env:
    - name: ENVIRONMENT
      value: "production"
    - name: LOG_LEVEL
      value: "info"

From ConfigMap

Reference a key from an existing ConfigMap:

env:
- name: DATABASE_HOST
  valueFrom:
    configMapKeyRef:
      name: app-config        # ConfigMap name
      key: db_host              # Key inside the ConfigMap

ConfigMap definition:

apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  db_host: "postgres.default.svc.cluster.local"
  db_port: "5432"

Exam Trap: configMapKeyRef.name refers to the ConfigMap object name, not the file name. The key must exist in the ConfigMap or the Pod will fail to start. Source: CKA Day 11

From Secret

Reference a key from an existing Secret:

env:
- name: DB_PASSWORD
  valueFrom:
    secretKeyRef:
      name: db-secret
      key: password

Secret definition:

apiVersion: v1
kind: Secret
metadata:
  name: db-secret
type: Opaque
data:
  password: c2VjcmV0MTIz   # base64 encoded value

Encode/decode helper:

echo -n "secret123" | base64       # Encode
echo "c2VjcmV0MTIz" | base64 -d   # Decode

Warning: Secrets are base64-encoded, not encrypted, by default. Anyone with read access to the Secret object can decode the values. Enable encryption at rest for production clusters. Source: CKA Day 11

Downward API: Pod-Generated Values

Kubernetes can inject metadata about the Pod itself as environment variables:

env:
- name: POD_NAME
  valueFrom:
    fieldRef:
      fieldPath: metadata.name
- name: POD_NAMESPACE
  valueFrom:
    fieldRef:
      fieldPath: metadata.namespace
- name: NODE_NAME
  valueFrom:
    fieldRef:
      fieldPath: spec.nodeName
- name: POD_IP
  valueFrom:
    fieldRef:
      fieldPath: status.podIP

fieldPath	Value Injected
metadata.name	Pod name
metadata.namespace	Pod namespace
metadata.uid	Pod unique ID
spec.nodeName	Node the Pod is running on
status.podIP	Pod’s internal IP address
status.hostIP	Node’s IP address

Injecting All ConfigMap Keys

Instead of referencing keys one by one, you can inject all key-value pairs from a ConfigMap as environment variables:

spec:
  containers:
  - name: my-app
    image: nginx
    envFrom:
    - configMapRef:
        name: app-config

This creates one environment variable per key in the ConfigMap. Caution: Key names must be valid environment variable names (no hyphens, must start with a letter or underscore).

Troubleshooting Environment Variables

# List env vars inside a running container
kubectl exec my-pod -- env | sort
 
# Check if a specific variable is set
kubectl exec my-pod -- sh -c 'echo $DB_PASSWORD'
 
# Verify ConfigMap contents
kubectl get configmap app-config -o yaml
 
# Verify Secret contents (base64 decoded)
kubectl get secret db-secret -o jsonpath='{.data.password}' | base64 -d

Issue	Cause	Fix
Variable not set	Typo in name or missing valueFrom	Check YAML spelling and indentation
Invalid value	ConfigMap/Secret key doesn’t exist	Verify the referenced object and key
CreateContainerConfigError	Secret or ConfigMap missing	Create the referenced object first
Base64 garbage	Forgot to encode value in Secret	Use `echo -n “value”

CKA Exam Patterns

# Quickly create a Pod with an env var
kubectl run debug --image=busybox --env="KEY=VALUE" --restart=Never -- sleep 3600
 
# Create a ConfigMap from literal values
kubectl create configmap app-config --from-literal=db_host=postgres --from-literal=db_port=5432
 
# Create a Secret from literal values (auto base64 encodes)
kubectl create secret generic db-secret --from-literal=password=secret123

Exam Tip: kubectl create secret automatically base64-encodes the value for you. You don’t need to encode manually when using the CLI. Source: CKA Day 11

Related Pages

• Pod Fundamentals — where env vars fit in the Pod spec
• Multi-Container Pods — injecting different env vars per container
• Init Containers — passing config to setup scripts
• Sidecar Pattern — configuring sidecars via env vars
• Deployment, ReplicaSet & Replication Controller — propagating env vars across replicas
• Kubernetes Namespaces — scope of ConfigMaps and Secrets
• Kubernetes Labels and Selectors — labeling Pods for env var injection patterns
• CKA Certification — exam domains where configuration appears
• CKA Study Roadmap — Day 11 in the 40-day plan

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Tags: kubernetes environment-variables configmap secret downward-api cka devops configuration