# Cloudformation Best Practices

> ALWAYS use this when the request matches Cloudformation Best Practices: CloudFormation template optimization, nested stacks, drift detection, and production-ready patterns.

- Skill: `anhvu1107/cloudformation-best-practices` (Agent Skill, multi-file: 6 files)
- Install (CLI): `npx skillmds@latest add anhvu1107/cloudformation-best-practices`
- Raw SKILL.md: https://api.skillmd.com/api/skills/anhvu1107/cloudformation-best-practices/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: anhvu1107 (https://skillmd.com/u/anhvu1107)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/anhvu1107/cloudformation-best-practices

---


## Selective Reading Rule

Start with:

- `references/senior-master-standard.md`
- `references/usage-routing.md`
- `references/quality-checklist.md`

Then load only the inherited docs, scripts, assets, or examples that match the user's actual task.

You are an expert in AWS CloudFormation specializing in template optimization, stack architecture, and production-grade infrastructure deployment.

## Use this skill when

- Writing or reviewing CloudFormation templates (YAML/JSON)
- Optimizing existing templates for maintainability and cost
- Designing nested or cross-stack architectures
- Troubleshooting stack creation/update failures and drift

## Do not use this skill when

- The user prefers CDK or Terraform over raw CloudFormation
- The task is application code, not infrastructure

## Instructions

1. Use YAML over JSON for readability.
2. Parameterize environment-specific values; use `Mappings` for static lookups.
3. Apply `DeletionPolicy: Retain` on stateful resources (RDS, S3, DynamoDB).
4. Use `Conditions` to support multi-environment templates.
5. Validate templates with `aws cloudformation validate-template` before deployment.
6. Prefer `!Sub` over `!Join` for string interpolation.

## Examples

### Example 1: Parameterized VPC Template

```yaml
AWSTemplateFormatVersion: "2010-09-09"
Description: Production VPC with public and private subnets

Parameters:
  Environment:
    Type: String
    AllowedValues: [dev, staging, prod]
  VpcCidr:
    Type: String
    Default: "10.0.0.0/16"

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

Resources:
  VPC:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: !Ref VpcCidr
      EnableDnsSupport: true
      EnableDnsHostnames: true
      Tags:
        - Key: Name
          Value: !Sub "${Environment}-vpc"

Outputs:
  VpcId:
    Value: !Ref VPC
    Export:
      Name: !Sub "${Environment}-VpcId"
```

## Best Practices

- ✅ **Do:** Use `Outputs` with `Export` for cross-stack references
- ✅ **Do:** Add `DeletionPolicy` and `UpdateReplacePolicy` on stateful resources
- ✅ **Do:** Use `cfn-lint` and `cfn-nag` in CI pipelines
- ❌ **Don't:** Hardcode ARNs or account IDs — use `!Sub` with pseudo parameters
- ❌ **Don't:** Put all resources in a single monolithic template

## Troubleshooting

**Problem:** Stack stuck in `UPDATE_ROLLBACK_FAILED`
**Solution:** Use `continue-update-rollback` with `--resources-to-skip` for the failing resource, then fix the root cause.

## Limitations
- Use this skill only when the task clearly matches the scope described above.
- Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
- Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.