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Mappings et Conditions

Mappings​

Les mappings sont des tables de correspondance clé-valeur statiques.

Syntaxe​

Mappings:
  MapName:
    TopLevelKey1:
      SecondLevelKey1: Value1
      SecondLevelKey2: Value2
    TopLevelKey2:
      SecondLevelKey1: Value3
      SecondLevelKey2: Value4

Cas d'usage : AMIs par région​

Mappings:
  RegionAMI:
    us-east-1:
      HVM64: ami-0ff8a91507f77f867
      HVM32: ami-0a584ac55a7631c0c
    us-west-1:
      HVM64: ami-0bdb828fd58c52235
      HVM32: ami-066ee5fd4a9ef77f1
    eu-west-1:
      HVM64: ami-047bb4163c506cd98
      HVM32: ami-0a7c483d527806435
    eu-west-2:
      HVM64: ami-0c55b159cbfafe1f0
      HVM32: ami-0b0d4b4f0b7f5f5e7
    ap-northeast-1:
      HVM64: ami-0ce107ae7af2e92b5
      HVM32: ami-0f9ae750e8274075b

Resources:
  Instance:
    Type: AWS::EC2::Instance
    Properties:
      ImageId: !FindInMap 
        - RegionAMI
        - !Ref AWS::Region
        - HVM64
      InstanceType: t3.micro

Cas d'usage : Configuration par environnement​

Mappings:
  EnvironmentConfig:
    development:
      InstanceType: t3.micro
      MinSize: 1
      MaxSize: 2
      MultiAZ: 'false'
      BackupRetention: 1
    staging:
      InstanceType: t3.small
      MinSize: 2
      MaxSize: 4
      MultiAZ: 'false'
      BackupRetention: 7
    production:
      InstanceType: t3.medium
      MinSize: 2
      MaxSize: 10
      MultiAZ: 'true'
      BackupRetention: 30

Parameters:
  Environment:
    Type: String
    AllowedValues:
      - development
      - staging
      - production
    Default: development

Resources:
  WebServerGroup:
    Type: AWS::AutoScaling::AutoScalingGroup
    Properties:
      MinSize: !FindInMap [EnvironmentConfig, !Ref Environment, MinSize]
      MaxSize: !FindInMap [EnvironmentConfig, !Ref Environment, MaxSize]
      LaunchTemplate:
        LaunchTemplateId: !Ref LaunchTemplate
        Version: !GetAtt LaunchTemplate.LatestVersionNumber

  LaunchTemplate:
    Type: AWS::EC2::LaunchTemplate
    Properties:
      LaunchTemplateData:
        InstanceType: !FindInMap [EnvironmentConfig, !Ref Environment, InstanceType]

FindInMap​

# Syntaxe complète
!FindInMap 
  - MapName
  - TopLevelKey
  - SecondLevelKey

# Syntaxe courte
!FindInMap [MapName, TopLevelKey, SecondLevelKey]

# Avec références
!FindInMap [RegionAMI, !Ref 'AWS::Region', HVM64]
!FindInMap [EnvironmentConfig, !Ref Environment, InstanceType]

Conditions​

Les conditions permettent de créer des ressources conditionnellement.

Définir des conditions​

Conditions:
  ConditionName: !Equals [value1, value2]

Fonctions de condition​

Conditions:
  # Equals - Égalité
  IsProduction: !Equals 
    - !Ref Environment
    - production

  # Not - Négation
  IsNotProduction: !Not 
    - !Equals [!Ref Environment, production]

  # And - ET logique
  IsProductionAndMultiAZ: !And 
    - !Equals [!Ref Environment, production]
    - !Equals [!Ref EnableMultiAZ, 'true']

  # Or - OU logique
  IsDevOrStaging: !Or 
    - !Equals [!Ref Environment, development]
    - !Equals [!Ref Environment, staging]

  # If - Conditionnel
  UseCustomAMI: !If 
    - HasCustomAMI
    - true
    - false

  # Condition sur un paramètre vide
  HasKeyPair: !Not 
    - !Equals [!Ref KeyPairName, '']

Conditions imbriquées​

Conditions:
  IsProduction: !Equals [!Ref Environment, production]
  
  EnableHA: !Equals [!Ref EnableHighAvailability, 'true']
  
  # Combiner des conditions
  IsProductionWithHA: !And
    - !Condition IsProduction
    - !Condition EnableHA

Utiliser les conditions​

Sur les ressources​

Conditions:
  CreateProdResources: !Equals [!Ref Environment, production]

Resources:
  # Cette ressource n'est créée qu'en production
  ProductionDatabase:
    Type: AWS::RDS::DBInstance
    Condition: CreateProdResources
    Properties:
      DBInstanceClass: db.r5.large
      MultiAZ: true
      # ...

  # Version dev/staging
  NonProdDatabase:
    Type: AWS::RDS::DBInstance
    Condition: IsNotProduction
    Properties:
      DBInstanceClass: db.t3.micro
      MultiAZ: false
      # ...

Dans les propriétés avec !If​

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

Resources:
  Database:
    Type: AWS::RDS::DBInstance
    Properties:
      DBInstanceClass: !If 
        - IsProduction
        - db.r5.large
        - db.t3.micro
      MultiAZ: !If [IsProduction, true, false]
      AllocatedStorage: !If [IsProduction, 100, 20]
      BackupRetentionPeriod: !If [IsProduction, 30, 1]
      DeletionProtection: !If [IsProduction, true, false]

AWS::NoValue pour supprimer des propriétés​

Conditions:
  HasKeyPair: !Not [!Equals [!Ref KeyPairName, '']]

Resources:
  Instance:
    Type: AWS::EC2::Instance
    Properties:
      InstanceType: t3.micro
      ImageId: !Ref AMIId
      # KeyName n'est défini que si un KeyPair est fourni
      KeyName: !If 
        - HasKeyPair
        - !Ref KeyPairName
        - !Ref AWS::NoValue

Sur les outputs​

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

Outputs:
  ProductionEndpoint:
    Condition: IsProduction
    Description: Endpoint de production
    Value: !GetAtt ProductionLoadBalancer.DNSName
    Export:
      Name: !Sub '${AWS::StackName}-ProdEndpoint'

Exemple complet​

AWSTemplateFormatVersion: '2010-09-09'
Description: Infrastructure avec conditions et mappings

Parameters:
  Environment:
    Type: String
    AllowedValues:
      - development
      - staging
      - production
    Default: development
  
  EnableMonitoring:
    Type: String
    AllowedValues:
      - 'true'
      - 'false'
    Default: 'true'

Mappings:
  EnvironmentConfig:
    development:
      InstanceType: t3.micro
      VolumeSize: 20
      MultiAZ: false
    staging:
      InstanceType: t3.small
      VolumeSize: 50
      MultiAZ: false
    production:
      InstanceType: t3.large
      VolumeSize: 100
      MultiAZ: true

  RegionAMI:
    eu-west-1:
      AMI: ami-0c55b159cbfafe1f0
    eu-west-2:
      AMI: ami-0a669382ea0feb73a
    us-east-1:
      AMI: ami-0ff8a91507f77f867

Conditions:
  IsProduction: !Equals [!Ref Environment, production]
  IsNotProduction: !Not [!Condition IsProduction]
  EnableDetailedMonitoring: !And
    - !Condition IsProduction
    - !Equals [!Ref EnableMonitoring, 'true']
  CreateAlarms: !Or
    - !Condition IsProduction
    - !Equals [!Ref EnableMonitoring, 'true']

Resources:
  # Instance EC2
  WebServer:
    Type: AWS::EC2::Instance
    Properties:
      InstanceType: !FindInMap [EnvironmentConfig, !Ref Environment, InstanceType]
      ImageId: !FindInMap [RegionAMI, !Ref 'AWS::Region', AMI]
      Monitoring: !If [EnableDetailedMonitoring, true, false]
      BlockDeviceMappings:
        - DeviceName: /dev/xvda
          Ebs:
            VolumeSize: !FindInMap [EnvironmentConfig, !Ref Environment, VolumeSize]
            VolumeType: gp3
      Tags:
        - Key: Name
          Value: !Sub '${AWS::StackName}-webserver'
        - Key: Environment
          Value: !Ref Environment

  # Base de données production uniquement
  ProductionDB:
    Type: AWS::RDS::DBInstance
    Condition: IsProduction
    DeletionPolicy: Snapshot
    Properties:
      DBInstanceClass: db.r5.large
      Engine: postgres
      MultiAZ: true
      StorageEncrypted: true
      AllocatedStorage: 100
      BackupRetentionPeriod: 30
      DeletionProtection: true

  # Base de données dev/staging
  NonProductionDB:
    Type: AWS::RDS::DBInstance
    Condition: IsNotProduction
    Properties:
      DBInstanceClass: db.t3.micro
      Engine: postgres
      MultiAZ: false
      AllocatedStorage: 20
      BackupRetentionPeriod: 1

  # Alarme CloudWatch conditionnelle
  CPUAlarm:
    Type: AWS::CloudWatch::Alarm
    Condition: CreateAlarms
    Properties:
      AlarmName: !Sub '${AWS::StackName}-HighCPU'
      MetricName: CPUUtilization
      Namespace: AWS/EC2
      Statistic: Average
      Period: 300
      EvaluationPeriods: 2
      Threshold: !If [IsProduction, 70, 90]
      ComparisonOperator: GreaterThanThreshold
      Dimensions:
        - Name: InstanceId
          Value: !Ref WebServer

Outputs:
  InstanceId:
    Description: ID de l'instance
    Value: !Ref WebServer

  DatabaseEndpoint:
    Description: Endpoint de la base de données
    Value: !If 
      - IsProduction
      - !GetAtt ProductionDB.Endpoint.Address
      - !GetAtt NonProductionDB.Endpoint.Address

  MonitoringStatus:
    Description: État du monitoring détaillé
    Value: !If [EnableDetailedMonitoring, 'Enabled', 'Disabled']

  ProductionDBArn:
    Condition: IsProduction
    Description: ARN de la DB production
    Value: !GetAtt ProductionDB.DBInstanceArn

Bonnes pratiques​

1. Nommer les conditions clairement​

# ✅ Bon - Nom descriptif
Conditions:
  IsProductionEnvironment: !Equals [!Ref Environment, production]
  ShouldCreateBackups: !Or [!Condition IsProductionEnvironment, ...]

# ❌ Mauvais - Nom cryptique
Conditions:
  C1: !Equals [!Ref Environment, production]

2. Éviter les conditions trop complexes​

# ❌ Trop complexe
Conditions:
  ComplexCondition: !And
    - !Or
      - !Equals [!Ref A, '1']
      - !And
        - !Equals [!Ref B, '2']
        - !Not [!Equals [!Ref C, '3']]
    - !Equals [!Ref D, '4']

# ✅ Décomposer
Conditions:
  IsA: !Equals [!Ref A, '1']
  IsBNotC: !And
    - !Equals [!Ref B, '2']
    - !Not [!Equals [!Ref C, '3']]
  IsAOrBNotC: !Or [!Condition IsA, !Condition IsBNotC]
  FinalCondition: !And [!Condition IsAOrBNotC, !Equals [!Ref D, '4']]

3. Utiliser les mappings pour les valeurs fixes​

# ✅ Mappings pour données statiques
Mappings:
  InstanceSizes:
    small:
      Type: t3.small
      Memory: 2048
    medium:
      Type: t3.medium
      Memory: 4096

# ❌ Éviter les !If imbriqués
InstanceType: !If 
  - IsSmall
  - t3.small
  - !If [IsMedium, t3.medium, t3.large]

Résumé​

  • Mappings : Tables statiques pour les correspondances région/config
  • Conditions : Logique booléenne pour le contrôle de flux
  • !FindInMap : Récupère une valeur dans un mapping
  • !If : Choisit une valeur selon une condition
  • Condition: sur une ressource : Création conditionnelle
  • AWS::NoValue : Supprime une propriété

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