LeftSize GitHub Action

Scan your AWS and Azure infrastructure for cost optimization opportunities using Cloud Custodian. Run scans directly in GitHub Actions - no infrastructure required from your side.

Features

🔍 Safe Scanning - 100% read-only operations, no changes to your infrastructure
☁️ Multi-Cloud - Supports Azure and AWS
🚀 Zero Config - Works out-of-the-box with sensible defaults
🔐 Secure - Uses OIDC for authentication, no secrets storage needed
📊 Actionable - Findings submitted to LeftSize dashboard for tracking
🎯 Customizable - Filter policies, add custom rules

Quick Start

Prerequisites

Install the LeftSize GitHub App
Complete onboarding to get your installation-id and repository-token
Configure cloud provider authentication (Azure or AWS)

Basic Usage (Azure)

name: LeftSize Cost Optimization Scanon:
schedule:
- cron: '0 0 * * *'# Daily at midnightworkflow_dispatch: # Manual triggerpermissions:
id-token: write # Required for OIDCcontents: readjobs:
leftsize-scan:
runs-on: ubuntu-lateststeps:
- name: Azure Login (OIDC)uses: azure/login@v1with:
client-id: ${{ secrets.AZURE_CLIENT_ID }}tenant-id: ${{ secrets.AZURE_TENANT_ID }}subscription-id: ${{ secrets.AZURE_SUBSCRIPTION_ID }}
- name: Run LeftSize Scanuses: leftsize/leftsize-action@v1with:
installation-id: ${{ secrets.LEFTSIZE_INSTALLATION_ID }}repository-token: ${{ secrets.LEFTSIZE_REPOSITORY_TOKEN }}

AWS Usage

permissions:
id-token: write # Required for OIDCcontents: readjobs:
leftsize-scan:
runs-on: ubuntu-lateststeps:
- name: AWS Login (OIDC)uses: aws-actions/configure-aws-credentials@v4with:
role-to-assume: ${{ secrets.AWS_ROLE_ARN }}aws-region: us-east-1
- name: Run LeftSize Scanuses: leftsize/leftsize-action@v1with:
installation-id: ${{ secrets.LEFTSIZE_INSTALLATION_ID }}repository-token: ${{ secrets.LEFTSIZE_REPOSITORY_TOKEN }}cloud-provider: aws

Configuration

Inputs

Input	Required	Default	Description
`installation-id`	✅ Yes	-	GitHub App installation ID from LeftSize onboarding
`repository-token`	✅ Yes	-	Secure repository token from LeftSize onboarding
`backend-url`	No	`https://api.leftsize.com`	LeftSize backend API URL
`cloud-provider`	No	`azure`	Cloud provider: `azure` or `aws`
`azure-subscription-ids`	No	All accessible	Comma-separated Azure subscription IDs to scan
`aws-regions`	No	All accessible	Comma-separated AWS regions to scan
`include-policies`	No	All	Policy categories: `cost-optimization`, `governance`, `security`
`exclude-policies`	No	None	Specific policy names to skip (comma-separated)
`verbose`	No	`false`	Enable verbose logging

Outputs

Output	Description
`findings-count`	Total number of findings detected
`findings-submitted`	Whether findings were successfully submitted (`true`/`false`)
`findings-json`	JSON string of all findings for custom processing

Advanced Examples

Multi-Subscription Azure Scan

permissions:
id-token: write # Required for OIDCcontents: readjobs:
leftsize-scan:
runs-on: ubuntu-lateststeps:
- uses: leftsize/leftsize-action@v1with:
installation-id: ${{ secrets.LEFTSIZE_INSTALLATION_ID }}repository-token: ${{ secrets.LEFTSIZE_REPOSITORY_TOKEN }}azure-subscription-ids: "sub-id-1,sub-id-2,sub-id-3"

AWS Multi-Region Scan

permissions:
id-token: write # Required for OIDCcontents: readjobs:
leftsize-scan:
runs-on: ubuntu-lateststeps:
- uses: leftsize/leftsize-action@v1with:
installation-id: ${{ secrets.LEFTSIZE_INSTALLATION_ID }}repository-token: ${{ secrets.LEFTSIZE_REPOSITORY_TOKEN }}cloud-provider: awsaws-regions: "us-east-1,eu-west-1,ap-southeast-1"

Filter Policies

permissions:
id-token: write # Required for OIDCcontents: readjobs:
leftsize-scan:
runs-on: ubuntu-lateststeps:
- uses: leftsize/leftsize-action@v1with:
installation-id: ${{ secrets.LEFTSIZE_INSTALLATION_ID }}repository-token: ${{ secrets.LEFTSIZE_REPOSITORY_TOKEN }}include-policies: cost-optimization,governance # Only cost and governance policiesexclude-policies: leftsize-idle-vm # Skip specific rule

Custom Processing of Findings

permissions:
id-token: write # Required for OIDCcontents: readjobs:
leftsize-scan:
runs-on: ubuntu-lateststeps:
- name: Run LeftSize Scanid: leftsizeuses: leftsize/leftsize-action@v1with:
installation-id: ${{ secrets.LEFTSIZE_INSTALLATION_ID }}repository-token: ${{ secrets.LEFTSIZE_REPOSITORY_TOKEN }}
- name: Process Findingsrun: | echo "Found ${{ steps.leftsize.outputs.findings-count }} findings" echo "Submitted: ${{ steps.leftsize.outputs.findings-submitted }}" # Custom processing echo '${{ steps.leftsize.outputs.findings-json }}' | jq '.[] | select(.severity == "high")'

Azure Setup (OIDC)

1. Create Azure AD App Registration

# Create app
az ad app create --display-name "LeftSize-GitHub-Action"# Get app ID
APP_ID=$(az ad app list --display-name "LeftSize-GitHub-Action" --query "[0].appId" -o tsv)# Create service principal
az ad sp create --id $APP_ID# Get object ID
OBJECT_ID=$(az ad sp list --display-name "LeftSize-GitHub-Action" --query "[0].id" -o tsv)

2. Configure Federated Credentials

# Create credential configuration
cat > credential.json <<EOF{ "name": "github-actions", "issuer": "https://token.actions.githubusercontent.com", "subject": "repo:YOUR-ORG/YOUR-REPO:ref:refs/heads/main", "audiences": ["api://AzureADTokenExchange"]}EOF# Add federated credential
az ad app federated-credential create --id $APP_ID --parameters credential.json

3. Assign Permissions

# Assign Reader role (minimum required)
az role assignment create \
--assignee $OBJECT_ID \
--role "Reader" \
--scope /subscriptions/YOUR-SUBSCRIPTION-ID
# Assign Monitoring Reader (for metrics)
az role assignment create \
--assignee $OBJECT_ID \
--role "Monitoring Reader" \
--scope /subscriptions/YOUR-SUBSCRIPTION-ID

4. Add Secrets to GitHub

Add these secrets to your repository:

AZURE_CLIENT_ID: App ID from step 1
AZURE_TENANT_ID: Your Azure AD tenant ID
AZURE_SUBSCRIPTION_ID: Your subscription ID
LEFTSIZE_INSTALLATION_ID: From LeftSize onboarding
LEFTSIZE_REPOSITORY_TOKEN: From LeftSize onboarding

AWS Setup (OIDC)

1. Create IAM OIDC Provider

aws iam create-open-id-connect-provider \
--url https://token.actions.githubusercontent.com \
--client-id-list sts.amazonaws.com \
--thumbprint-list 6938fd4d98bab03faadb97b34396831e3780aea1

2. Create IAM Role

{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Principal": {
"Federated": "arn:aws:iam::ACCOUNT-ID:oidc-provider/token.actions.githubusercontent.com"
},
"Action": "sts:AssumeRoleWithWebIdentity",
"Condition": {
"StringEquals": {
"token.actions.githubusercontent.com:aud": "sts.amazonaws.com",
"token.actions.githubusercontent.com:sub": "repo:YOUR-ORG/YOUR-REPO:ref:refs/heads/main"
}
}
}
]
}

3. Attach Read-Only Policies

aws iam attach-role-policy \
--role-name LeftSize-GitHub-Action \
--policy-arn arn:aws:iam::aws:policy/ReadOnlyAccess

4. Add Secrets to GitHub

AWS_ROLE_ARN: ARN of the role created above
LEFTSIZE_INSTALLATION_ID: From LeftSize onboarding
LEFTSIZE_REPOSITORY_TOKEN: From LeftSize onboarding

Policies Included

The action includes curated Cloud Custodian policies:

Cost Optimization (Azure)

leftsize-idle-vm - Idle virtual machines
leftsize-unattached-disk - Unattached managed disks
leftsize-unused-public-ip - Unused public IP addresses
leftsize-idle-app-service-plan - Underutilized App Service Plans
leftsize-idle-app-service-plan-no-apps - Empty App Service Plans
leftsize-inactive-azure-load-balancer - Inactive load balancers

Cost Optimization (AWS)

leftsize-idle-ecs-instances - Idle ECS container instances
leftsize-unattached-ebs-volumes - Unattached EBS volumes
leftsize-unused-elastic-ips - Unused Elastic IPs
leftsize-old-snapshots - Old EBS snapshots
And more...

Governance

Security group rules
Unencrypted resources
Missing tags
And more...

Runner Requirements

⚠️Important: This action requires a Linux runner (ubuntu-latest, ubuntu-20.04, or ubuntu-22.04). It does not work on Windows or macOS runners due to Docker-based action limitations.

jobs:
leftsize-scan:
runs-on: ubuntu-latest # Required

Pricing

LeftSize runs on your GitHub Actions runners, not our infrastructure:

Free tier: 2000 minutes/month (GitHub Free)
Typical scan: 3-5 minutes
Result: ~400 scans/month on free tier

For larger organizations, use self-hosted runners for unlimited usage.

Security

✅ No Cloud Credentials Stored - Uses OIDC (keyless authentication)
✅ Read-Only Operations - All policies are 100% safe, no destructive actions
✅ Multi-Tenant Secure - Repository tokens prevent cross-tenant attacks
✅ Minimal Permissions - Only requires Reader and Monitoring Reader roles

Troubleshooting

Authentication Failed

Azure:

# Test authentication locally
az login
az account show
# Verify service principal
az ad sp show --id $AZURE_CLIENT_ID

AWS:

# Test authentication locally
aws sts get-caller-identity
# Verify role trust policy
aws iam get-role --role-name LeftSize-GitHub-Action

No Findings

This is normal! It means your infrastructure is well-optimized. The action will still submit a report with zero findings.

Findings Not Submitted

Check:

LEFTSIZE_INSTALLATION_ID is correct
LEFTSIZE_REPOSITORY_TOKEN matches your repository
Backend URL is reachable (https://api.leftsize.com)

Findings are saved as artifacts even if submission fails.

Support

License

MIT License - See LICENSE file for details.

Contributing

Contributions welcome! Please read CONTRIBUTING.md for guidelines.

Made with ❤️ by the LeftSize team

Name		Name	Last commit message	Last commit date
.github/workflows		.github/workflows
policies		policies
tests		tests
.gitignore		.gitignore
AGENTS.md		AGENTS.md
CHANGELOG.md		CHANGELOG.md
DEPLOYMENT.md		DEPLOYMENT.md
Dockerfile		Dockerfile
LICENSE		LICENSE
README.md		README.md
SUMMARY.md		SUMMARY.md
action.yml		action.yml
entrypoint.sh		entrypoint.sh
pytest.ini		pytest.ini
requirements.txt		requirements.txt
run.py		run.py
stats.py		stats.py

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LeftSize GitHub Action

Features

Quick Start

Prerequisites

Basic Usage (Azure)

AWS Usage

Configuration

Inputs

Outputs

Advanced Examples

Multi-Subscription Azure Scan

AWS Multi-Region Scan

Filter Policies

Custom Processing of Findings

Azure Setup (OIDC)

1. Create Azure AD App Registration

2. Configure Federated Credentials

3. Assign Permissions

4. Add Secrets to GitHub

AWS Setup (OIDC)

1. Create IAM OIDC Provider

2. Create IAM Role

3. Attach Read-Only Policies

4. Add Secrets to GitHub

Policies Included

Cost Optimization (Azure)

Cost Optimization (AWS)

Governance

Runner Requirements

Pricing

Security

Troubleshooting

Authentication Failed

No Findings

Findings Not Submitted

Support

License

Contributing

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