Handism's Tech Blog

AWSTemplateFormatVersion: '2010-09-09'
Description: 'Multi-tenant SaaS Architecture with tenant isolation and best practices'

Parameters:
  Environment:
    Type: String
    Default: prod
    AllowedValues:
      - dev
      - prod
    Description: Environment name

  TenantIsolationModel:
    Type: String
    Default: pool
    AllowedValues:
      - pool
      - silo
    Description: Tenant isolation model (pool=shared resources, silo=dedicated resources)

Resources:
  # Cognito User Pool for tenant user authentication
  TenantUserPool:
    Type: AWS::Cognito::UserPool
    Properties:
      UserPoolName: !Sub '${AWS::StackName}-tenant-users'
      AutoVerifiedAttributes:
        - email
      Schema:
        - Name: email
          Required: true
          Mutable: false
        - Name: tenant_id
          AttributeDataType: String
          Mutable: false
      Policies:
        PasswordPolicy:
          MinimumLength: 12
          RequireUppercase: true
          RequireLowercase: true
          RequireNumbers: true
          RequireSymbols: true
      AccountRecoverySetting:
        RecoveryMechanisms:
          - Name: verified_email
            Priority: 1

  TenantUserPoolClient:
    Type: AWS::Cognito::UserPoolClient
    Properties:
      UserPoolId: !Ref TenantUserPool
      GenerateSecret: false
      ExplicitAuthFlows:
        - ALLOW_USER_SRP_AUTH
        - ALLOW_REFRESH_TOKEN_AUTH
      PreventUserExistenceErrors: ENABLED

  # DynamoDB Table for tenant metadata
  TenantMetadataTable:
    Type: AWS::DynamoDB::Table
    Properties:
      BillingMode: PAY_PER_REQUEST
      AttributeDefinitions:
        - AttributeName: tenant_id
          AttributeType: S
      KeySchema:
        - AttributeName: tenant_id
          KeyType: HASH
      PointInTimeRecoverySpecification:
        PointInTimeRecoveryEnabled: true
      SSESpecification:
        SSEEnabled: true
      StreamSpecification:
        StreamViewType: NEW_AND_OLD_IMAGES

  # DynamoDB Table for tenant data with tenant_id partition
  TenantDataTable:
    Type: AWS::DynamoDB::Table
    Properties:
      BillingMode: PAY_PER_REQUEST
      AttributeDefinitions:
        - AttributeName: tenant_id
          AttributeType: S
        - AttributeName: item_id
          AttributeType: S
      KeySchema:
        - AttributeName: tenant_id
          KeyType: HASH
        - AttributeName: item_id
          KeyType: RANGE
      PointInTimeRecoverySpecification:
        PointInTimeRecoveryEnabled: true
      SSESpecification:
        SSEEnabled: true

  # S3 Bucket for tenant data with prefix-based isolation
  TenantDataBucket:
    Type: AWS::S3::Bucket
    Properties:
      BucketEncryption:
        ServerSideEncryptionConfiguration:
          - ServerSideEncryptionByDefault:
              SSEAlgorithm: AES256
      PublicAccessBlockConfiguration:
        BlockPublicAcls: true
        BlockPublicPolicy: true
        IgnorePublicAcls: true
        RestrictPublicBuckets: true
      LifecycleConfiguration:
        Rules:
          - Id: TransitionToIA
            Status: Enabled
            Transitions:
              - TransitionInDays: 90
                StorageClass: INTELLIGENT_TIERING
      VersioningConfiguration:
        Status: Enabled

  # Lambda Execution Role with tenant isolation policies
  TenantApiRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
          - Effect: Allow
            Principal:
              Service: lambda.amazonaws.com
            Action: sts:AssumeRole
      ManagedPolicyArns:
        - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
      Policies:
        - PolicyName: TenantDataAccess
          PolicyDocument:
            Version: '2012-10-17'
            Statement:
              - Effect: Allow
                Action:
                  - dynamodb:GetItem
                  - dynamodb:PutItem
                  - dynamodb:Query
                  - dynamodb:UpdateItem
                  - dynamodb:DeleteItem
                Resource: 
                  - !GetAtt TenantDataTable.Arn
                  - !GetAtt TenantMetadataTable.Arn
              - Effect: Allow
                Action:
                  - s3:GetObject
                  - s3:PutObject
                  - s3:DeleteObject
                Resource: !Sub '${TenantDataBucket.Arn}/*'

  # Lambda Function for tenant API with ARM64
  TenantApiFunction:
    Type: AWS::Lambda::Function
    Properties:
      Runtime: python3.13
      Handler: index.handler
      Architectures:
        - arm64
      MemorySize: 256
      Timeout: 30
      Role: !GetAtt TenantApiRole.Arn
      Environment:
        Variables:
          TENANT_DATA_TABLE: !Ref TenantDataTable
          TENANT_METADATA_TABLE: !Ref TenantMetadataTable
          TENANT_BUCKET: !Ref TenantDataBucket
          ISOLATION_MODEL: !Ref TenantIsolationModel
      Code:
        ZipFile: |
          import json
          import os
          import boto3
          from datetime import datetime
          
          dynamodb = boto3.resource('dynamodb')
          data_table = dynamodb.Table(os.environ['TENANT_DATA_TABLE'])
          metadata_table = dynamodb.Table(os.environ['TENANT_METADATA_TABLE'])
          
          def handler(event, context):
              try:
                  # Extract tenant_id from JWT claims
                  claims = event.get('requestContext', {}).get('authorizer', {}).get('claims', {})
                  tenant_id = claims.get('custom:tenant_id')
                  
                  if not tenant_id:
                      return {
                          'statusCode': 403,
                          'body': json.dumps({'error': 'Tenant ID not found'})
                      }
                  
                  method = event['httpMethod']
                  
                  if method == 'GET':
                      response = data_table.query(
                          KeyConditionExpression='tenant_id = :tid',
                          ExpressionAttributeValues={':tid': tenant_id}
                      )
                      return {
                          'statusCode': 200,
                          'headers': {'Content-Type': 'application/json'},
                          'body': json.dumps(response['Items'])
                      }
                  
                  elif method == 'POST':
                      body = json.loads(event['body'])
                      item = {
                          'tenant_id': tenant_id,
                          'item_id': body['item_id'],
                          'data': body.get('data', ''),
                          'timestamp': datetime.utcnow().isoformat()
                      }
                      data_table.put_item(Item=item)
                      return {
                          'statusCode': 201,
                          'headers': {'Content-Type': 'application/json'},
                          'body': json.dumps(item)
                      }
                  
                  return {
                      'statusCode': 405,
                      'body': json.dumps({'error': 'Method not allowed'})
                  }
              
              except Exception as e:
                  return {
                      'statusCode': 500,
                      'body': json.dumps({'error': str(e)})
                  }
      LoggingConfig:
        LogGroup: !Ref TenantApiLogGroup

  TenantApiLogGroup:
    Type: AWS::Logs::LogGroup
    Properties:
      RetentionInDays: 30

  # Lambda Function for tenant onboarding
  TenantOnboardingFunction:
    Type: AWS::Lambda::Function
    Properties:
      Runtime: python3.13
      Handler: index.handler
      Architectures:
        - arm64
      MemorySize: 256
      Timeout: 60
      Role: !GetAtt TenantOnboardingRole.Arn
      Environment:
        Variables:
          TENANT_METADATA_TABLE: !Ref TenantMetadataTable
          USER_POOL_ID: !Ref TenantUserPool
      Code:
        ZipFile: |
          import json
          import os
          import boto3
          from datetime import datetime
          import uuid
          
          dynamodb = boto3.resource('dynamodb')
          metadata_table = dynamodb.Table(os.environ['TENANT_METADATA_TABLE'])
          cognito = boto3.client('cognito-idp')
          
          def handler(event, context):
              try:
                  body = json.loads(event['body'])
                  tenant_id = str(uuid.uuid4())
                  
                  # Create tenant metadata
                  tenant_metadata = {
                      'tenant_id': tenant_id,
                      'tenant_name': body['tenant_name'],
                      'tier': body.get('tier', 'standard'),
                      'status': 'active',
                      'created_at': datetime.utcnow().isoformat()
                  }
                  metadata_table.put_item(Item=tenant_metadata)
                  
                  return {
                      'statusCode': 201,
                      'headers': {'Content-Type': 'application/json'},
                      'body': json.dumps({
                          'tenant_id': tenant_id,
                          'message': 'Tenant created successfully'
                      })
                  }
              
              except Exception as e:
                  return {
                      'statusCode': 500,
                      'body': json.dumps({'error': str(e)})
                  }
      LoggingConfig:
        LogGroup: !Ref TenantOnboardingLogGroup

  TenantOnboardingRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
          - Effect: Allow
            Principal:
              Service: lambda.amazonaws.com
            Action: sts:AssumeRole
      ManagedPolicyArns:
        - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
      Policies:
        - PolicyName: TenantOnboardingAccess
          PolicyDocument:
            Version: '2012-10-17'
            Statement:
              - Effect: Allow
                Action:
                  - dynamodb:PutItem
                  - dynamodb:GetItem
                Resource: !GetAtt TenantMetadataTable.Arn
              - Effect: Allow
                Action:
                  - cognito-idp:AdminCreateUser
                  - cognito-idp:AdminSetUserPassword
                Resource: !GetAtt TenantUserPool.Arn

  TenantOnboardingLogGroup:
    Type: AWS::Logs::LogGroup
    Properties:
      RetentionInDays: 30

  # API Gateway REST API
  TenantApi:
    Type: AWS::ApiGateway::RestApi
    Properties:
      Name: !Sub '${AWS::StackName}-tenant-api'
      Description: Multi-tenant SaaS API
      EndpointConfiguration:
        Types:
          - REGIONAL

  # Cognito Authorizer
  ApiAuthorizer:
    Type: AWS::ApiGateway::Authorizer
    Properties:
      Name: CognitoAuthorizer
      Type: COGNITO_USER_POOLS
      RestApiId: !Ref TenantApi
      IdentitySource: method.request.header.Authorization
      ProviderARNs:
        - !GetAtt TenantUserPool.Arn

  # API Resources
  DataResource:
    Type: AWS::ApiGateway::Resource
    Properties:
      RestApiId: !Ref TenantApi
      ParentId: !GetAtt TenantApi.RootResourceId
      PathPart: data

  OnboardingResource:
    Type: AWS::ApiGateway::Resource
    Properties:
      RestApiId: !Ref TenantApi
      ParentId: !GetAtt TenantApi.RootResourceId
      PathPart: onboarding

  # API Methods for tenant data
  DataMethodGet:
    Type: AWS::ApiGateway::Method
    Properties:
      RestApiId: !Ref TenantApi
      ResourceId: !Ref DataResource
      HttpMethod: GET
      AuthorizationType: COGNITO_USER_POOLS
      AuthorizerId: !Ref ApiAuthorizer
      Integration:
        Type: AWS_PROXY
        IntegrationHttpMethod: POST
        Uri: !Sub 'arn:${AWS::Partition}:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${TenantApiFunction.Arn}/invocations'

  DataMethodPost:
    Type: AWS::ApiGateway::Method
    Properties:
      RestApiId: !Ref TenantApi
      ResourceId: !Ref DataResource
      HttpMethod: POST
      AuthorizationType: COGNITO_USER_POOLS
      AuthorizerId: !Ref ApiAuthorizer
      Integration:
        Type: AWS_PROXY
        IntegrationHttpMethod: POST
        Uri: !Sub 'arn:${AWS::Partition}:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${TenantApiFunction.Arn}/invocations'

  # API Method for tenant onboarding
  OnboardingMethodPost:
    Type: AWS::ApiGateway::Method
    Properties:
      RestApiId: !Ref TenantApi
      ResourceId: !Ref OnboardingResource
      HttpMethod: POST
      AuthorizationType: NONE
      Integration:
        Type: AWS_PROXY
        IntegrationHttpMethod: POST
        Uri: !Sub 'arn:${AWS::Partition}:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${TenantOnboardingFunction.Arn}/invocations'

  # API Deployment
  ApiDeployment:
    Type: AWS::ApiGateway::Deployment
    DependsOn:
      - DataMethodGet
      - DataMethodPost
      - OnboardingMethodPost
    Properties:
      RestApiId: !Ref TenantApi

  # API Stage
  ApiStage:
    Type: AWS::ApiGateway::Stage
    Properties:
      RestApiId: !Ref TenantApi
      DeploymentId: !Ref ApiDeployment
      StageName: !Ref Environment
      TracingEnabled: true
      MethodSettings:
        - ResourcePath: '/*'
          HttpMethod: '*'
          LoggingLevel: INFO
          DataTraceEnabled: false
          MetricsEnabled: true
          ThrottlingBurstLimit: 500
          ThrottlingRateLimit: 100

  # Lambda Permissions
  TenantApiInvokePermission:
    Type: AWS::Lambda::Permission
    Properties:
      FunctionName: !Ref TenantApiFunction
      Action: lambda:InvokeFunction
      Principal: apigateway.amazonaws.com
      SourceArn: !Sub 'arn:${AWS::Partition}:execute-api:${AWS::Region}:${AWS::AccountId}:${TenantApi}/*/*'

  OnboardingApiInvokePermission:
    Type: AWS::Lambda::Permission
    Properties:
      FunctionName: !Ref TenantOnboardingFunction
      Action: lambda:InvokeFunction
      Principal: apigateway.amazonaws.com
      SourceArn: !Sub 'arn:${AWS::Partition}:execute-api:${AWS::Region}:${AWS::AccountId}:${TenantApi}/*/*'

  # CloudWatch Alarms
  TenantApiErrorAlarm:
    Type: AWS::CloudWatch::Alarm
    Properties:
      AlarmDescription: Alert when tenant API errors exceed threshold
      MetricName: Errors
      Namespace: AWS/Lambda
      Statistic: Sum
      Period: 300
      EvaluationPeriods: 1
      Threshold: 10
      ComparisonOperator: GreaterThanThreshold
      Dimensions:
        - Name: FunctionName
          Value: !Ref TenantApiFunction

  ApiGatewayErrorAlarm:
    Type: AWS::CloudWatch::Alarm
    Properties:
      AlarmDescription: Alert when API Gateway 5xx errors exceed threshold
      MetricName: 5XXError
      Namespace: AWS/ApiGateway
      Statistic: Sum
      Period: 300
      EvaluationPeriods: 1
      Threshold: 10
      ComparisonOperator: GreaterThanThreshold
      Dimensions:
        - Name: ApiName
          Value: !Sub '${AWS::StackName}-tenant-api'

Outputs:
  ApiEndpoint:
    Description: Tenant API endpoint URL
    Value: !Sub 'https://${TenantApi}.execute-api.${AWS::Region}.amazonaws.com/${Environment}'
    Export:
      Name: !Sub '${AWS::StackName}-ApiEndpoint'

  UserPoolId:
    Description: Cognito User Pool ID for tenant authentication
    Value: !Ref TenantUserPool
    Export:
      Name: !Sub '${AWS::StackName}-UserPoolId'

  UserPoolClientId:
    Description: Cognito User Pool Client ID
    Value: !Ref TenantUserPoolClient
    Export:
      Name: !Sub '${AWS::StackName}-UserPoolClientId'

  TenantMetadataTableName:
    Description: DynamoDB table for tenant metadata
    Value: !Ref TenantMetadataTable
    Export:
      Name: !Sub '${AWS::StackName}-MetadataTable'

  TenantDataTableName:
    Description: DynamoDB table for tenant data
    Value: !Ref TenantDataTable
    Export:
      Name: !Sub '${AWS::StackName}-DataTable'

  TenantDataBucketName:
    Description: S3 bucket for tenant data
    Value: !Ref TenantDataBucket
    Export:
      Name: !Sub '${AWS::StackName}-DataBucket'
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