Environment variables in Lambda in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

How does Lambda handle environment variables during execution?

Consider an AWS Lambda function configured with environment variables. What happens if you update an environment variable value in the Lambda console while the function is running?

A The running function continues using the old environment variable value until it finishes; new invocations use the updated value.

B The running function immediately uses the new environment variable value without restart.

C The running function throws an error due to environment variable change.

D The Lambda service restarts all running instances immediately to apply the new environment variable.

💡 Hint

Think about how environment variables are loaded when a Lambda function starts.

Lambda loads environment variables when a function instance starts. Changing environment variables affects only new instances or new invocations after restart. Running instances keep using the old values.

❓ security

intermediate

Which environment variable setting improves Lambda security?

You want to store sensitive data like API keys in Lambda environment variables. Which option best improves security?

A Use environment variables only for non-sensitive data and hardcode secrets in code.

B Encrypt environment variables using AWS KMS and enable encryption in Lambda settings.

C Store secrets in environment variables without encryption but restrict IAM roles.

D Store secrets directly as plain text environment variables.

💡 Hint

Think about how AWS helps protect sensitive data in Lambda.

Encrypting environment variables with AWS KMS ensures secrets are protected at rest and decrypted only during function execution, improving security.

❓ Configuration

advanced

What is the correct way to reference an environment variable in a Node.js Lambda function?

Given an environment variable named API_ENDPOINT, which code snippet correctly accesses its value inside a Node.js Lambda handler?

AWS

exports.handler = async (event) => {
  // Access environment variable here
};

A const endpoint = process.env.API_ENDPOINT.value;

B const endpoint = process.env['API_ENDPOINT'];

C const endpoint = process.env.get('API_ENDPOINT');

D const endpoint = process.env.API_ENDPOINT;

💡 Hint

Recall how environment variables are accessed in Node.js.

In Node.js, environment variables are accessed via process.env.VARIABLE_NAME. Both dot notation and bracket notation work, but dot notation is simpler and common.

❓ Architecture

advanced

How to manage environment variables across multiple Lambda functions in different environments?

You have multiple Lambda functions deployed in development, staging, and production. What is the best practice to manage environment variables for these environments?

A Hardcode environment variables in each Lambda function code for each environment.

B Use the same environment variables for all environments to avoid confusion.

C Use separate Lambda environment variable configurations per environment and manage them via infrastructure as code tools.

D Store environment variables in a shared S3 file and read it at runtime from each Lambda.

💡 Hint

Think about how to keep environment variables consistent and manageable across environments.

Using infrastructure as code (like CloudFormation or Terraform) to define environment variables per environment ensures consistency, version control, and easy updates.

🧠 Conceptual

expert

What happens if a Lambda environment variable exceeds the size limit?

AWS Lambda has a size limit for all environment variables combined. What is the result if you try to deploy a Lambda function with environment variables exceeding this limit?

A The deployment fails with an error indicating environment variables size exceeded.

B The Lambda function deploys successfully but truncates environment variables at the limit.

C The Lambda function runs but environment variables are ignored at runtime.

D AWS automatically compresses environment variables to fit the limit.

💡 Hint

Consider AWS Lambda deployment constraints and error handling.

AWS Lambda enforces a hard limit on total environment variable size. Deployments exceeding this limit fail with an error, preventing deployment.

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