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Remediating Unused Lambda Functions

This tutorial demonstrates how to identify and delete unused Lambda functions with zero invocations in the past 30 days.

Overview​

Unused Lambda functions create unnecessary clutter and potential security risks from outdated dependencies. While the cost savings are minimal (Lambda functions only incur storage costs after the first 512MB free tier), removing unused functions improves operational hygiene and reduces attack surface.

Prerequisites​

  • AWS Console access with Lambda permissions
  • Target function: remediation-lambda-unused-func

Step 1: Navigate to Lambda Functions Console​

Navigate to the Lambda Functions console in the us-east-1 region.

Lambda Functions List

This view shows all Lambda functions in the region. You can see the function name, description, package type, runtime, and last modified date.

Step 2: Open Function Details​

Click on the function name remediation-lambda-unused-func to view its details and configuration.

Function Overview

The function overview shows basic information including description, ARN, application association, and the function diagram showing layers and triggers.

Step 3: Check Monitoring Metrics​

Click the Monitor tab to view invocation metrics and verify the function is unused.

Monitoring Tab

The monitoring tab displays CloudWatch metrics for the function. Initially, the view shows the last 3 hours of data. To verify usage over the past 30 days, change the time range.

Step 4: Verify Zero Invocations Over 30 Days​

Click the time range selector and choose 4w to view 4 weeks of data.

Zero Invocations

The invocations graph shows "No data available" across all metrics (Invocations, Duration, Errors, Throttles, etc.), confirming the function has had zero invocations over the past 4 weeks.

Step 5: Check for Triggers​

Click the Configuration tab, then select Triggers from the left menu to verify there are no active event sources.

Check Triggers

The Triggers section shows "No triggers" configured, indicating the function has no event sources like EventBridge, API Gateway, or S3 that would invoke it.

Step 6: Delete the Function​

Click the Actions dropdown button in the top right and select Delete function.

Delete Option

The Actions menu provides various function operations. Select "Delete function" to begin the deletion process.

Step 7: Confirm Deletion​

AWS requires typing "confirm" in the text field to prevent accidental deletion.

Delete Confirmation

Type confirm in the field and click Delete. The warning explains that deletion permanently removes the function code, though related logs, roles, test event schemas, and triggers are retained.

Step 8: Verify Deletion​

After deletion, you're returned to the functions list with a success message.

Deletion Complete

The success message confirms "Your Lambda function remediation-lambda-unused-func was successfully deleted." The function no longer appears in the functions list, which now shows 2 functions instead of the original 3.

Alternative Approaches​

AWS CLI​

Delete a function using the AWS CLI:

aws lambda delete-function \
  --function-name remediation-lambda-unused-func \
  --region us-east-1

Infrastructure as Code​

Remove the function from your CloudFormation template or Terraform configuration and apply the changes:

# CloudFormation
aws cloudformation update-stack --stack-name my-stack --template-body file://template.yaml

# Terraform
terraform apply

Bulk Cleanup​

For large-scale cleanup, export the function list and delete multiple unused functions via script:

# List all functions
aws lambda list-functions --region us-east-1 --query 'Functions[*].[FunctionName]' --output text

# Delete multiple functions
for func in $(cat unused-functions.txt); do
  aws lambda delete-function --function-name "$func" --region us-east-1
done

Archive Before Delete​

If uncertain about deletion, export the function code first:

# Download function code
aws lambda get-function --function-name remediation-lambda-unused-func \
  --query 'Code.Location' --output text | xargs curl -o function.zip

# Store in S3 for safekeeping
aws s3 cp function.zip s3://my-backup-bucket/lambda-functions/remediation-lambda-unused-func.zip

Cost Impact​

Unused Lambda functions have minimal direct costs:

  • Storage: Free for first 512MB, then $0.03/GB-month
  • No invocation charges for unused functions

The primary benefits of deletion are:

  • Reduced security risk from outdated dependencies
  • Cleaner operational environment
  • Simplified resource management

Summary​

Successfully deleted the unused Lambda function by:

  1. Confirming zero invocations over 30 days via CloudWatch metrics
  2. Verifying no active triggers or event sources
  3. Using the AWS Console delete function with confirmation
  4. Validating the function was removed from the functions list

Deletion is immediate and irreversible. Always verify function usage before deletion.