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infrastructure/cloud-aws/cloudformation/references/cfn-syntax.md

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+# CloudFormation Syntax Reference
+
+## Template Structure
+
+```yaml
+AWSTemplateFormatVersion: '2010-09-09'
+Description: My CloudFormation Template
+
+Parameters:
+  Environment:
+    Type: String
+    AllowedValues: [dev, staging, prod]
+
+Mappings:
+  RegionMap:
+    us-east-1:
+      AMI: ami-12345678
+
+Conditions:
+  IsProd: !Equals [!Ref Environment, prod]
+
+Resources:
+  MyBucket:
+    Type: AWS::S3::Bucket
+    Properties:
+      BucketName: !Sub '${AWS::StackName}-bucket'
+
+Outputs:
+  BucketName:
+    Value: !Ref MyBucket
+    Export:
+      Name: !Sub '${AWS::StackName}-bucket'
+```
+
+## Intrinsic Functions
+
+```yaml
+# Reference
+!Ref MyResource
+
+# GetAtt
+!GetAtt MyResource.Arn
+
+# Sub (string substitution)
+!Sub '${AWS::StackName}-resource'
+!Sub 
+  - 'arn:aws:s3:::${Bucket}/*'
+  - Bucket: !Ref MyBucket
+
+# Join
+!Join ['-', [!Ref Environment, app]]
+
+# Select
+!Select [0, !GetAZs '']
+
+# Split
+!Split [',', 'a,b,c']
+
+# If
+!If [IsProd, 3, 1]
+
+# ImportValue
+!ImportValue ExportedValue
+```
+
+## Common Patterns
+
+### Cross-Stack References
+```yaml
+# Stack A - Export
+Outputs:
+  VpcId:
+    Value: !Ref VPC
+    Export:
+      Name: SharedVPC
+
+# Stack B - Import
+Resources:
+  Subnet:
+    Type: AWS::EC2::Subnet
+    Properties:
+      VpcId: !ImportValue SharedVPC
+```
+
+### Nested Stacks
+```yaml
+Resources:
+  VPCStack:
+    Type: AWS::CloudFormation::Stack
+    Properties:
+      TemplateURL: https://s3.amazonaws.com/bucket/vpc.yaml
+      Parameters:
+        Environment: !Ref Environment
+```
+
+### DependsOn
+```yaml
+Resources:
+  MyInstance:
+    Type: AWS::EC2::Instance
+    DependsOn: MySecurityGroup
+```
+
+## CLI Commands
+
+```bash
+# Create stack
+aws cloudformation create-stack \
+  --stack-name mystack \
+  --template-body file://template.yaml \
+  --parameters ParameterKey=Environment,ParameterValue=prod
+
+# Update stack
+aws cloudformation update-stack \
+  --stack-name mystack \
+  --template-body file://template.yaml
+
+# Delete stack
+aws cloudformation delete-stack --stack-name mystack
+
+# Validate template
+aws cloudformation validate-template --template-body file://template.yaml
+```