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Janak Shrestha
Janak Shrestha

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Day 57: Print Environment Variables

#kubernetes #devops

The Nautilus DevOps team is working on to setup some pre-requisites for an application that will send the greetings to different users. There is a sample deployment, that needs to be tested. Below is a scenario which needs to be configured on Kubernetes cluster. Please find below more details about it.

  1. Create a pod named print-envars-greeting.
  3. Configure spec as, the container name should be print-env-container and use bash image.

  5. Create three environment variables:
    a. GREETING and its value should be Welcome to
    b. COMPANY and its value should be Nautilus
    c. GROUP and its value should be Group

  6. Use command ["/bin/sh", "-c", 'echo "$(GREETING) $(COMPANY) $(GROUP)"'] (please use this exact command), also set its restartPolicy policy to Never to avoid crash loop back.

  7. You can check the output using kubectl logs -f print-envars-greeting command.

Note: The kubectl utility on the jump-host has been configured to work with the Kubernetes cluster.

What We Will Build

We are going to create a Kubernetes Pod that:

  • Runs a container using the bash image
  • Defines three environment variables
  • Executes a command that prints these variables
  • Exits after completing its task

Technical Details

Component Specification
Pod Name print-envars-greeting
Container Name print-env-container
Image bash
Restart Policy Never
Environment Variables GREETING, COMPANY, GROUP

Understanding Environment Variables in Kubernetes

Environment variables are key-value pairs that provide configuration data to containers. They are commonly used for:

  • Application configuration
  • Database connection strings
  • API endpoints
  • Feature flags
  • Credentials (though Secrets are recommended for sensitive data)

In Kubernetes, environment variables can be defined directly in the Pod specification using the env field.

Step-by-Step Implementation

Step 1: Create the Pod YAML File

Create a file named print-envars-greeting.yaml with the following content:

apiVersion: v1
kind: Pod
metadata:
  name: print-envars-greeting
spec:
  restartPolicy: Never
  containers:
  - name: print-env-container
    image: bash
    command:
    - "/bin/sh"
    - "-c"
    - 'echo "$(GREETING) $(COMPANY) $(GROUP)"'
    env:
    - name: GREETING
      value: "Welcome to"
    - name: COMPANY
      value: "Nautilus"
    - name: GROUP
      value: "Group"
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YAML Breakdown

Pod Metadata

metadata:
  name: print-envars-greeting
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This defines the name of the Pod.

Restart Policy

spec:
  restartPolicy: Never
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Never ensures the Pod runs once and does not restart. Since this is a one-time task, this policy is appropriate.

Container Definition

containers:
- name: print-env-container
  image: bash
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The container is named print-env-container and uses the bash image, which provides a lightweight shell environment.

Command Definition

command:
- "/bin/sh"
- "-c"
- 'echo "$(GREETING) $(COMPANY) $(GROUP)"'
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The command executes a shell script that echoes the values of the three environment variables.

Environment Variables

env:
- name: GREETING
  value: "Welcome to"
- name: COMPANY
  value: "Nautilus"
- name: GROUP
  value: "Group"
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Three environment variables are defined with their respective values.

Step 2: Create the Pod

Apply the YAML configuration to create the Pod:

kubectl apply -f print-envars-greeting.yaml
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Output:

pod/print-envars-greeting created
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Step 3: Verify Pod Status

Check the status of the Pod:

kubectl get pods
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Output:

NAME                    READY   STATUS      RESTARTS   AGE
print-envars-greeting   0/1     Completed   0          11s
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The Completed status indicates that the container ran successfully and exited. Since the restart policy is Never, the Pod remains in this completed state.

Step 4: View the Output

View the logs to see the output of the command:

kubectl logs print-envars-greeting
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Output:

Welcome to Nautilus Group
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How the Command Works

The command executes as follows:

  1. The container starts with the bash image
  2. The shell interprets the command
  3. The shell substitutes each $(VARIABLE_NAME) with its value:
    • $(GREETING) → Welcome to
    • $(COMPANY) → Nautilus
    • $(GROUP) → Group
  4. The echo command prints the concatenated string
  5. The container exits successfully

The command syntax is important. The single quotes preserve the $ characters, allowing the shell to interpret them as variable references rather than treating them as literal strings.

Environment Variable Best Practices

When to Use Environment Variables

Environment variables are ideal for:

  • Non-sensitive configuration
  • Application settings that differ between environments
  • Feature toggles
  • Service discovery information

When Not to Use Environment Variables

Consider alternatives for:

  • Sensitive data (use Secrets instead)
  • Large configuration files (use ConfigMaps)
  • Complex nested configurations (use ConfigMaps or external configuration management)

Best Practices

  1. Use descriptive names: Make variable names meaningful and consistent
  2. Document your variables: Maintain a reference of what each variable does
  3. Use Secrets for sensitive data: Never store passwords or tokens in plain text
  4. Keep it organized: Group related variables together
  5. Validate variables: Ensure required variables are set before the application starts

Common Use Cases

Application Configuration

Environment variables are commonly used to configure applications:

env:
- name: DATABASE_URL
  value: "postgres://user:pass@host:5432/db"
- name: LOG_LEVEL
  value: "debug"
- name: API_KEY
  value: "abcdef123456"
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Feature Flags

Control application features:

env:
- name: FEATURE_NEW_UI
  value: "true"
- name: FEATURE_BETA
  value: "false"
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Environment Identification

Identify the deployment environment:

env:
- name: ENVIRONMENT
  value: "production"
- name: REGION
  value: "us-east-1"
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Troubleshooting

Pod Does Not Start 

# Check the Pod status
kubectl get pods

# Get detailed information
kubectl describe pod print-envars-greeting

# Check logs for errors
kubectl logs print-envars-greeting
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Variables Not Substituted

Ensure you are using the correct syntax:

  • Use $(VAR_NAME) for variable substitution
  • Use single quotes to preserve $ characters
  • Verify that the variable names match exactly

Pod Is in CrashLoopBackOff 

# Check the pod status
kubectl get pods

# Check logs
kubectl logs print-envars-greeting --previous

# Verify the command syntax
kubectl describe pod print-envars-greeting
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Key Takeaways

What We Learned

  1. Environment variables in Kubernetes: Defined in the env field of a container specification
  2. Variable substitution: Use $(VAR_NAME) to reference environment variables in commands
  3. Restart policies: Never is suitable for one-time tasks
  4. Pod lifecycle: A Pod can have a Completed status after successful execution
  5. Command execution: The bash image provides a lightweight shell environment

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