Cloudformation Agent Skill

Deploy AWS resources with CloudFormation templates. Create stacks, use nested stacks, and implement drift detection. Use when deploying AWS-native IaC.

4k tokens

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the whole folder, loaded on every use

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instructions only

copies elsewhere

how many repositories repackaged it

511

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on the repository, not the skill itself

Install

one command, takes just this skill from the repository

npx skills add https://github.com/BagelHole/DevOps-Security-Agent-Skills --skill cloudformation

What comes with it

2 064 bytes besides the instruction

references/cfn-syntax.md

The instruction itself

13 sections, as written by the author

CloudFormation

Deploy AWS infrastructure with native CloudFormation templates, change sets, nested stacks, and drift detection.

When to Use This Skill

Deploying AWS resources using AWS-native Infrastructure as Code
Creating repeatable, parameterized infrastructure templates
Managing multi-environment deployments (dev, staging, prod) with the same template
Implementing safe deployments with change sets and rollback protection
Detecting and remediating configuration drift
Organizing large infrastructure into nested stacks
Exporting/importing values between stacks

Prerequisites

AWS CLI v2 installed and configured
IAM permissions: cloudformation:*, plus permissions for all resources in the template
(Optional) cfn-lint installed for template validation (pip install cfn-lint)
S3 bucket for storing templates larger than 51,200 bytes

Template Structure

AWSTemplateFormatVersion: '2010-09-09'
Description: Production web application infrastructure

Metadata:
  AWS::CloudFormation::Interface:
    ParameterGroups:
      - Label: { default: "Environment" }
        Parameters: [Environment, InstanceType]
      - Label: { default: "Network" }
        Parameters: [VpcId, SubnetIds]

Parameters:
  Environment:
    Type: String
    AllowedValues: [dev, staging, prod]
    Default: dev

  InstanceType:
    Type: String
    Default: t3.micro
    AllowedValues: [t3.micro, t3.small, t3.medium, t3.large]

  VpcId:
    Type: AWS::EC2::VPC::Id
    Description: VPC to deploy into

  SubnetIds:
    Type: List<AWS::EC2::Subnet::Id>
    Description: Subnets for the application

Conditions:
  IsProd: !Equals [!Ref Environment, prod]
  CreateReadReplica: !Equals [!Ref Environment, prod]

Mappings:
  RegionAMI:
    us-east-1:
      AL2023: ami-0abcdef1234567890
    us-west-2:
      AL2023: ami-0fedcba9876543210

Resources:
  SecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: !Sub '${Environment}-web-sg'
      VpcId: !Ref VpcId
      SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: 443
          ToPort: 443
          CidrIp: 0.0.0.0/0
      Tags:
        - Key: Name
          Value: !Sub '${Environment}-web-sg'

  LaunchTemplate:
    Type: AWS::EC2::LaunchTemplate
    Properties:
      LaunchTemplateName: !Sub '${Environment}-web'
      LaunchTemplateData:
        ImageId: !FindInMap [RegionAMI, !Ref 'AWS::Region', AL2023]
        InstanceType: !If [IsProd, t3.large, !Ref InstanceType]
        MetadataOptions:
          HttpTokens: required
        SecurityGroupIds:
          - !Ref SecurityGroup

  AutoScalingGroup:
    Type: AWS::AutoScaling::AutoScalingGroup
    Properties:
      AutoScalingGroupName: !Sub '${Environment}-web-asg'
      LaunchTemplate:
        LaunchTemplateId: !Ref LaunchTemplate
        Version: !GetAtt LaunchTemplate.LatestVersionNumber
      MinSize: !If [IsProd, 2, 1]
      MaxSize: !If [IsProd, 10, 3]
      DesiredCapacity: !If [IsProd, 4, 1]
      VPCZoneIdentifier: !Ref SubnetIds
      TargetGroupARNs:
        - !Ref TargetGroup
      HealthCheckType: ELB
      HealthCheckGracePeriod: 300
      Tags:
        - Key: Name
          Value: !Sub '${Environment}-web'
          PropagateAtLaunch: true
    UpdatePolicy:
      AutoScalingRollingUpdate:
        MinInstancesInService: !If [IsProd, 2, 0]
        MaxBatchSize: 1
        PauseTime: PT5M
        WaitOnResourceSignals: true
        SuspendProcesses:
          - HealthCheck
          - ReplaceUnhealthy
          - AZRebalance
          - AlarmNotification
          - ScheduledActions

  TargetGroup:
    Type: AWS::ElasticLoadBalancingV2::TargetGroup
    Properties:
      Name: !Sub '${Environment}-web-tg'
      Port: 8080
      Protocol: HTTP
      VpcId: !Ref VpcId
      TargetType: instance
      HealthCheckPath: /health
      HealthCheckIntervalSeconds: 30
      HealthyThresholdCount: 2
      UnhealthyThresholdCount: 3

Outputs:
  SecurityGroupId:
    Description: Web security group ID
    Value: !Ref SecurityGroup
    Export:
      Name: !Sub '${Environment}-WebSecurityGroup'

  AutoScalingGroupName:
    Description: ASG name
    Value: !Ref AutoScalingGroup
    Export:
      Name: !Sub '${Environment}-WebASG'

Stack Operations

# Validate a template
aws cloudformation validate-template --template-body file://template.yaml

# Lint with cfn-lint (catches more issues)
cfn-lint template.yaml

# Create a stack
aws cloudformation create-stack \
  --stack-name production-web \
  --template-body file://template.yaml \
  --parameters \
    ParameterKey=Environment,ParameterValue=prod \
    ParameterKey=VpcId,ParameterValue=vpc-abc123 \
    ParameterKey=SubnetIds,ParameterValue="subnet-aaa\\,subnet-bbb" \
  --capabilities CAPABILITY_IAM CAPABILITY_NAMED_IAM \
  --tags Key=Environment,Value=production Key=Team,Value=platform \
  --enable-termination-protection \
  --on-failure ROLLBACK

# Wait for stack creation
aws cloudformation wait stack-create-complete --stack-name production-web

# Describe stack status and outputs
aws cloudformation describe-stacks \
  --stack-name production-web \
  --query "Stacks[0].{Status:StackStatus,Outputs:Outputs}" \
  --output table

# List stack resources
aws cloudformation list-stack-resources --stack-name production-web \
  --query "StackResourceSummaries[].{Logical:LogicalResourceId,Physical:PhysicalResourceId,Type:ResourceType,Status:ResourceStatus}" \
  --output table

# Delete a stack
aws cloudformation delete-stack --stack-name dev-web
aws cloudformation wait stack-delete-complete --stack-name dev-web

Change Sets (Safe Updates)

# Create a change set to preview changes before applying
aws cloudformation create-change-set \
  --stack-name production-web \
  --change-set-name update-instance-type \
  --template-body file://template.yaml \
  --parameters \
    ParameterKey=Environment,ParameterValue=prod \
    ParameterKey=InstanceType,ParameterValue=t3.large \
    ParameterKey=VpcId,UsePreviousValue=true \
    ParameterKey=SubnetIds,UsePreviousValue=true \
  --capabilities CAPABILITY_IAM

# Describe the change set to review planned changes
aws cloudformation describe-change-set \
  --stack-name production-web \
  --change-set-name update-instance-type \
  --query "Changes[].{Action:ResourceChange.Action,Resource:ResourceChange.LogicalResourceId,Type:ResourceChange.ResourceType,Replacement:ResourceChange.Replacement}" \
  --output table

# Execute the change set (apply changes)
aws cloudformation execute-change-set \
  --stack-name production-web \
  --change-set-name update-instance-type

# Wait for update
aws cloudformation wait stack-update-complete --stack-name production-web

# Delete a change set without applying
aws cloudformation delete-change-set \
  --stack-name production-web \
  --change-set-name update-instance-type

Drift Detection

# Start drift detection
DRIFT_ID=$(aws cloudformation detect-stack-drift \
  --stack-name production-web \
  --query 'StackDriftDetectionId' --output text)

# Check drift detection status
aws cloudformation describe-stack-drift-detection-status \
  --stack-drift-detection-id $DRIFT_ID

# View drifted resources
aws cloudformation describe-stack-resource-drifts \
  --stack-name production-web \
  --stack-resource-drift-status-filters MODIFIED DELETED \
  --query "StackResourceDrifts[].{Resource:LogicalResourceId,Status:StackResourceDriftStatus,Differences:PropertyDifferences}" \
  --output table

# Detect drift on a specific resource
aws cloudformation detect-stack-resource-drift \
  --stack-name production-web \
  --logical-resource-id SecurityGroup

Nested Stacks

Parent template:

AWSTemplateFormatVersion: '2010-09-09'
Description: Parent stack - full application

Parameters:
  Environment:
    Type: String
    AllowedValues: [dev, staging, prod]

Resources:
  NetworkStack:
    Type: AWS::CloudFormation::Stack
    Properties:
      TemplateURL: https://s3.amazonaws.com/my-cfn-templates/network.yaml
      Parameters:
        Environment: !Ref Environment
        VpcCidr: "10.0.0.0/16"
      Tags:
        - Key: Environment
          Value: !Ref Environment

  DatabaseStack:
    Type: AWS::CloudFormation::Stack
    DependsOn: NetworkStack
    Properties:
      TemplateURL: https://s3.amazonaws.com/my-cfn-templates/database.yaml
      Parameters:
        Environment: !Ref Environment
        VpcId: !GetAtt NetworkStack.Outputs.VpcId
        SubnetIds: !GetAtt NetworkStack.Outputs.PrivateSubnetIds

  AppStack:
    Type: AWS::CloudFormation::Stack
    DependsOn: [NetworkStack, DatabaseStack]
    Properties:
      TemplateURL: https://s3.amazonaws.com/my-cfn-templates/app.yaml
      Parameters:
        Environment: !Ref Environment
        VpcId: !GetAtt NetworkStack.Outputs.VpcId
        SubnetIds: !GetAtt NetworkStack.Outputs.PrivateSubnetIds
        DbEndpoint: !GetAtt DatabaseStack.Outputs.Endpoint

Outputs:
  VpcId:
    Value: !GetAtt NetworkStack.Outputs.VpcId
  AppUrl:
    Value: !GetAtt AppStack.Outputs.LoadBalancerDNS

# Package nested templates (uploads local references to S3)
aws cloudformation package \
  --template-file parent.yaml \
  --s3-bucket my-cfn-templates \
  --output-template-file packaged.yaml

# Deploy the packaged template
aws cloudformation deploy \
  --template-file packaged.yaml \
  --stack-name production-app \
  --parameter-overrides Environment=prod \
  --capabilities CAPABILITY_IAM CAPABILITY_AUTO_EXPAND \
  --tags Environment=production

Intrinsic Functions Reference

# Ref - reference a parameter or resource
SecurityGroupId: !Ref SecurityGroup

# GetAtt - get an attribute of a resource
SecurityGroupArn: !GetAtt SecurityGroup.GroupId

# Sub - string substitution
BucketName: !Sub '${Environment}-${AWS::AccountId}-data'

# Join - concatenate strings
PolicyArn: !Join ['', ['arn:aws:iam::', !Ref 'AWS::AccountId', ':policy/MyPolicy']]

# Select - pick from a list
FirstSubnet: !Select [0, !Ref SubnetIds]

# Split - split a string
FirstPart: !Select [0, !Split ['-', !Ref 'AWS::StackName']]

# If - conditional value
InstanceSize: !If [IsProd, t3.large, t3.micro]

# Equals - condition definition
Conditions:
  IsProd: !Equals [!Ref Environment, prod]

# ImportValue - cross-stack reference
VpcId: !ImportValue production-VpcId

# Cidr - generate CIDR blocks
Subnets: !Cidr [!GetAtt VPC.CidrBlock, 6, 8]

# GetAZs - list availability zones
AZ: !Select [0, !GetAZs '']

Stack Policy (Prevent Accidental Replacements)

# Apply a stack policy that prevents replacement of the database
aws cloudformation set-stack-policy \
  --stack-name production-web \
  --stack-policy-body '{
    "Statement": [
      {
        "Effect": "Allow",
        "Action": "Update:*",
        "Principal": "*",
        "Resource": "*"
      },
      {
        "Effect": "Deny",
        "Action": "Update:Replace",
        "Principal": "*",
        "Resource": "LogicalResourceId/Database"
      },
      {
        "Effect": "Deny",
        "Action": "Update:Delete",
        "Principal": "*",
        "Resource": "LogicalResourceId/Database"
      }
    ]
  }'

Stack Events and Debugging

# View stack events (most recent first)
aws cloudformation describe-stack-events \
  --stack-name production-web \
  --query "StackEvents[?ResourceStatus=='CREATE_FAILED' || ResourceStatus=='UPDATE_FAILED'].{Time:Timestamp,Resource:LogicalResourceId,Status:ResourceStatus,Reason:ResourceStatusReason}" \
  --output table

# Continue a rollback that is stuck
aws cloudformation continue-update-rollback \
  --stack-name production-web \
  --resources-to-skip SecurityGroup

# Cancel an in-progress update
aws cloudformation cancel-update-stack --stack-name production-web

# Get template from an existing stack
aws cloudformation get-template \
  --stack-name production-web \
  --template-stage Processed \
  --query TemplateBody \
  --output text > current-template.yaml

Troubleshooting

| Problem | Cause | Fix |

|---|---|---|

| CREATE_FAILED on IAM resource | Missing CAPABILITY_IAM | Add --capabilities CAPABILITY_IAM CAPABILITY_NAMED_IAM |

| Stack stuck in UPDATE_ROLLBACK_FAILED | Resource cannot be rolled back | Use continue-update-rollback with --resources-to-skip |

| Nested stack fails | Template URL wrong or S3 access denied | Use aws cloudformation package to upload; check bucket policy |

| Circular dependency error | Two resources reference each other | Break the cycle with a third resource or use DependsOn |

| Drift detected | Manual changes made outside CloudFormation | Re-apply the template or update template to match current state |

| Change set shows no changes | Template and parameters identical | Verify the diff; check if the change is parameter-only |

| Template validation error | YAML syntax or invalid resource property | Run cfn-lint; check property names against docs |

| Export name already exists | Another stack uses the same export name | Use unique export names with !Sub '${AWS::StackName}-Name' |

| Delete fails - resource in use | Dependent resource outside the stack | Remove the dependency first; check for SG references |

terraform-aws - Alternative IaC with Terraform
aws-iam - IAM resources in templates
aws-vpc - Network infrastructure templates
aws-ec2 - Compute resources in templates
aws-s3 - Storage resources in templates

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Copy the folder

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Install what it needs

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Cloudformation Agent Skill

Install

What comes with it

The instruction itself

CloudFormation

When to Use This Skill

Prerequisites

Template Structure

Stack Operations

Change Sets (Safe Updates)

Drift Detection

Nested Stacks

Intrinsic Functions Reference

Stack Policy (Prevent Accidental Replacements)

Stack Events and Debugging

Troubleshooting

Related Skills

Other skills for the same job

How to use it