aws-cloudformation-rds

# AWS CloudFormation RDS Database

## Overview

Create production-ready Amazon RDS infrastructure using AWS CloudFormation templates. Covers RDS instances (MySQL, PostgreSQL, Aurora), DB clusters, multi-AZ deployments, parameter groups, subnet groups, security groups, and cross-stack references.

## When to Use

- Creating RDS instances (MySQL, PostgreSQL, Aurora) or DB clusters with read replicas
- Setting up multi-AZ deployments or configuring parameter/subnet groups
- Integrating with Secrets Manager or implementing cross-stack references

## Quick Reference

| Component | CloudFormation Type | Use Case |
|-----------|-------------------|----------|
| DB Instance | `AWS::RDS::DBInstance` | Single database instance |
| DB Cluster | `AWS::RDS::DBCluster` | Aurora cluster |
| DB Subnet Group | `AWS::RDS::DBSubnetGroup` | VPC deployment |
| Parameter Group | `AWS::RDS::DBParameterGroup` | Database configuration |
| Security Group | `AWS::EC2::SecurityGroup` | Network access control |
| Secrets Manager | `AWS::SecretsManager::Secret` | Credential storage |

## Instructions

### Step 1 — Define Database Parameters

Use AWS-specific parameter types for validation.

```yaml
Parameters:
  DBInstanceClass:
    Type: AWS::RDS::DBInstance::InstanceType
    Default: db.t3.micro
    AllowedValues: [db.t3.micro, db.t3.small, db.t3.medium]

  Engine:
    Type: String
    Default: mysql
    AllowedValues: [mysql, postgres, aurora-mysql, aurora-postgresql]

  MasterUsername:
    Type: String
    Default: admin
    AllowedPattern: "^[a-zA-Z][a-zA-Z0-9]*$"
    MinLength: 1
    MaxLength: 16

  MasterUserPassword:
    Type: String
    NoEcho: true
    MinLength: 8
    MaxLength: 41
```

See [template-structure.md](references/template-structure.md) for advanced parameter patterns, mappings, conditions, and cross-stack references.

### Step 2 — Create DB Subnet Group

Required for VPC deployment with subnets in different AZs.

```yaml
DBSubnetGroup:
  Type: AWS::RDS::DBSubnetGroup
  Properties:
    DBSubnetGroupDescription: Subnet group for RDS
    SubnetIds:
      - !Ref PrivateSubnet1
      - !Ref PrivateSubnet2
```

See [database-components.md](references/database-components.md) for parameter groups, option groups, and engine-specific configurations.

### Step 3 — Configure Security Group

Restrict access to application tier only.

```yaml
DBSecurityGroup:
  Type: AWS::EC2::SecurityGroup
  Properties:
    GroupDescription: Security group for RDS
    VpcId: !Ref VpcId
    SecurityGroupIngress:
      - IpProtocol: tcp
        FromPort: 3306
        ToPort: 3306
        SourceSecurityGroupId: !Ref AppSecurityGroup
```

See [security-secrets.md](references/security-secrets.md) for VPC security groups, encryption, Secrets Manager integration, and IAM authentication.

### Step 4 — Launch RDS Instance

Configure instance with subnet group, security group, and settings.

```yaml
DBInstance:
  Type: AWS::RDS::DBInstance
  Properties:
    DBInstanceIdentifier: !Sub "${AWS::StackName}-mysql"
    DBInstanceClass: !Ref DBInstanceClass
    Engine: !Ref Engine
    MasterUsername: !Ref MasterUsername
    MasterUserPassword: !Ref MasterUserPassword
    AllocatedStorage: 20
    StorageType: gp3
    DBSubnetGroupName: !Ref DBSubnetGroup
    VPCSecurityGroups: [!Ref DBSecurityGroup]
    StorageEncrypted: true
    MultiAZ: true
    BackupRetentionPeriod: 7
    DeletionProtection: false
```

See [database-components.md](references/database-components.md) for MySQL, PostgreSQL, Aurora cluster configurations, and parameter groups.

### Step 5 — Enable High Availability

Configure multi-AZ deployment for production.

```yaml
Conditions:
  IsProduction: !Equals [!Ref Environment, production]

Resources:
  DBInstance:
    Type: AWS::RDS::DBInstance
    Properties:
      MultiAZ: !If [IsProduction, true, false]
      BackupRetentionPeriod: !If [IsProduction, 35, 7]
      DeletionProtection: !If [IsProduction, true, false]
      EnablePerformanceInsights: !If [IsProduction, true, false]
```

See [high-availability.md](references/high-availability.md) for multi-AZ deployments, read replicas, Aurora auto-scaling, enhanced monitoring, and disaster recovery.

### Step 6 — Define Outputs

Export connection details for application stacks.

```yaml
Outputs:
  DBInstanceEndpoint:
    Description: Database endpoint address
    Value: !GetAtt DBInstance.Endpoint.Address
    Export:
      Name: !Sub ${AWS::StackName}-DBEndpoint

  DBInstancePort:
    Description: Database port
    Value: !GetAtt DBInstance.Endpoint.Port
    Export:
      Name: !Sub ${AWS::StackName}-DBPort

  DBConnectionString:
    Description: Connection string
    Value: !Sub jdbc:mysql://${DBInstance.Endpoint.Address}:${DBInstance.Endpoint.Port}/${DBName}
```

See [template-structure.md](references/template-structure.md) for cross-stack reference patterns and import/export strategies.

### Validation Steps

Always validate before deploying, especially to production.

```bash
# Validate the template syntax
aws cloudformation validate-template --template-body file://template.yaml

# Review the change set before applying updates
aws cloudformation create-change-set \
  --stack-name my-rds-stack \
  --template-body file://template.yaml \
  --change-set-type UPDATE

aws cloudformation describe-change-set --change-set-name <arn>

# Execute the change set if the preview looks correct
aws cloudformation execute-change-set --change-set-name <arn>
```

## Best Practices

| Category | Practice | Implementation |
|----------|----------|----------------|
| Security | Encryption at rest | `StorageEncrypted: true` with KMS key |
| Security | Credential management | Use Secrets Manager integration |
| Security | Network isolation | Private subnets, restrictive SG rules |
| Security | IAM authentication | Enable `IAMDatabaseAuthentication` |
| HA | Multi-AZ deployment | `MultiAZ: true` for production |
| HA | Deletion protection | `DeletionProtection: true` for production |
| HA | Backup