Environment variables in Lambda in AWS - Mini Project: Build & Apply

Environment variables in Lambda

📖 Scenario: You are building a simple AWS Lambda function that needs to use environment variables to store configuration values securely and separately from the code.This is like keeping your house keys in a safe place instead of leaving them on the door. Environment variables help your Lambda function access important settings without hardcoding them.

🎯 Goal: Create an AWS Lambda function configuration that includes environment variables. You will first define the Lambda function, then add environment variables, and finally complete the configuration to deploy the Lambda function with these variables.

📋 What You'll Learn

Create a Lambda function resource with a name MyLambdaFunction.

Add an environment variables block with two variables: STAGE set to dev and LOG_LEVEL set to info.

Complete the Lambda function configuration with a runtime and handler.

💡 Why This Matters

🌍 Real World

Environment variables in Lambda functions allow you to separate configuration from code, making your functions more flexible and secure.

💼 Career

Knowing how to configure environment variables in Lambda is essential for cloud developers and DevOps engineers managing serverless applications.

1

Create the Lambda function resource

Create a resource block for an AWS Lambda function named MyLambdaFunction using AWS CloudFormation syntax.

AWS

# Your code here

Hint

Start by defining the Resources section and add a resource named MyLambdaFunction with type AWS::Lambda::Function.

2

Add environment variables block

Inside the MyLambdaFunction resource, add a property called Environment with a nested Variables map containing STAGE set to dev and LOG_LEVEL set to info.

AWS

Resources:
  MyLambdaFunction:
    Type: AWS::Lambda::Function
    # Add Environment variables block here

Hint

Use the Properties section to add Environment and then Variables with the two key-value pairs.

3

Add runtime and handler properties

Add the Runtime property set to python3.12 and the Handler property set to index.handler inside the Properties of MyLambdaFunction.

AWS

Resources:
  MyLambdaFunction:
    Type: AWS::Lambda::Function
    Properties:
      Environment:
        Variables:
          STAGE: dev
          LOG_LEVEL: info
      # Add Runtime and Handler here

Hint

Remember to add Runtime and Handler at the same level as Environment inside Properties.

4

Complete the Lambda function configuration

Add a Role property with the value arn:aws:iam::123456789012:role/lambda-execution-role inside the Properties of MyLambdaFunction to complete the configuration.

AWS

Resources:
  MyLambdaFunction:
    Type: AWS::Lambda::Function
    Properties:
      Runtime: python3.12
      Handler: index.handler
      Environment:
        Variables:
          STAGE: dev
          LOG_LEVEL: info
      # Add Role property here

Hint

The Role property is required for Lambda to have permission to run. Add it inside Properties.

Practice

1. What is the main purpose of environment variables in an AWS Lambda function?

easy

A. To store configuration settings outside the code for flexibility

B. To write logs directly to CloudWatch

C. To increase the memory allocated to the Lambda function

D. To define the runtime language of the Lambda function

Solution

1. Step 1: Understand environment variables role

   Environment variables hold configuration data separate from code, making functions flexible.

2. Step 2: Compare with other options

   Logging, memory, and runtime are unrelated to environment variables.

3. Final Answer:

   To store configuration settings outside the code for flexibility -> Option A

4. Quick Check:

   Environment variables = configuration outside code [OK]

Hint: Environment variables hold config, not code or logs [OK]

Common Mistakes:

• Confusing environment variables with logging settings
• Thinking environment variables control memory or runtime
• Assuming environment variables store code

2. Which of the following is the correct way to define an environment variable named API_KEY with value 12345 in AWS Lambda console?

easy

A. Create a CloudWatch alarm named API_KEY with threshold 12345

B. Add a tag with key API_KEY and value 12345

C. Write export API_KEY=12345 in the Lambda function code

D. Set key as API_KEY and value as 12345 in the Environment Variables section

Solution

1. Step 1: Identify environment variable setup

   Environment variables are set as key-value pairs in the Lambda console's Environment Variables section.

2. Step 2: Eliminate incorrect options

   Tags, code exports, and CloudWatch alarms do not define environment variables.

3. Final Answer:

   Set key as API_KEY and value as 12345 in the Environment Variables section -> Option D

4. Quick Check:

   Environment variables = key-value pairs in Lambda console [OK]

Hint: Set env vars in Lambda console's Environment Variables section [OK]

Common Mistakes:

• Confusing tags with environment variables
• Trying to set env vars inside code with export
• Using unrelated AWS features like CloudWatch alarms

3. Given this Python Lambda function code:

import os
def lambda_handler(event, context):
    return os.environ.get('MODE', 'default')

If the environment variable MODE is set to production, what will the function return?

medium

A. "default"

B. None

C. "production"

D. An error occurs

Solution

1. Step 1: Understand os.environ.get usage

   os.environ.get('MODE', 'default') returns the value of MODE if set, else 'default'.

2. Step 2: Apply given environment variable

   Since MODE is set to 'production', the function returns 'production'.

3. Final Answer:

   "production" -> Option C

4. Quick Check:

   Env var MODE='production' returns 'production' [OK]

Hint: os.environ.get returns env var value or default if missing [OK]

Common Mistakes:

• Assuming default is always returned
• Expecting None if variable exists
• Thinking code throws error if env var exists

4. A developer sets an environment variable DB_PASSWORD in Lambda console but the function code returns None when accessing it. What is the most likely cause?

medium

A. Lambda function memory is too low

B. The environment variable key is misspelled in the code

C. The environment variable value is encrypted and inaccessible

D. The Lambda function timeout is too short

Solution

1. Step 1: Check environment variable access

   If code returns None, likely the key used in code does not match the set key.

2. Step 2: Exclude unrelated causes

   Memory size, encryption, or timeout do not cause None return for env var access.

3. Final Answer:

   The environment variable key is misspelled in the code -> Option B

4. Quick Check:

   Misspelled env var key returns None [OK]

Hint: Check spelling of env var keys in code vs console [OK]

Common Mistakes:

• Blaming memory or timeout for env var issues
• Assuming encryption blocks access without decryption
• Not verifying exact key names

5. You want to securely store a database password in a Lambda environment variable but avoid exposing it in plain text. Which approach is best practice?

hard

A. Use AWS Lambda environment variables with encryption enabled and grant decryption permissions

B. Hardcode the password directly in the Lambda function code

C. Store the password in a public S3 bucket and read it at runtime

D. Send the password as a query parameter in API requests

Solution

1. Step 1: Understand secure storage options

   Lambda environment variables support encryption with AWS KMS and access control.

2. Step 2: Evaluate other options

   Hardcoding, public S3, or sending passwords in query parameters expose secrets and are insecure.

3. Final Answer:

   Use AWS Lambda environment variables with encryption enabled and grant decryption permissions -> Option A

4. Quick Check:

   Encrypted env vars + permissions = secure secret storage [OK]

Hint: Encrypt env vars and control access for secrets [OK]

Common Mistakes:

• Hardcoding secrets in code
• Using public storage for passwords
• Exposing secrets in API requests