Constructs

Construct Levels:

The construct library includes 3 level of constructs available to us.

• L1 Cfn Resources
  • these constructs are very low level. They represent CloudFormation resources, and require you to explicitly configure all resource properties which requires a deep understanding of the CloudFormation resource model.
• L2 Intent based Resources
  • L2 constructs allow us to represent AWS resources in a higher-level context, where we focus on intent-based definitions. This is done via CDK's implementation of default boilerplate, and common best practice logic.
• L3 Patterns
  • The highest level of constructs are known as patterns. These are common tasks defined by AWS that involve multiple kinds resources.

Examples

Level 1 Construct CfnVPC

Here I create a level 1 vpc construct. This construct has 1 required property cidrBlock which you can see matches exactly with the required properties in CloudFormation for VPC creation CloudFormation Definition.

new ec2.CfnVPC(this, 'level1-vpc', {
            cidrBlock: "10.0.0.0/16"
  })

If we take a look at the construct tree produced by this we can see that only 1 resource is being created during synthesis of our CDK

construct-tree
`-- my-new-stack
     `-- level1-vpc

Level 2 Construct VPC

Now from the same package ec2 I will make a VPC using the level 2 construct. Note that this has 0 required properties

new ec2.Vpc(this, 'level2-vpc', {

})

Unlike the level 1 construct we can see that this construct tree will create and manage MANY more AWS resources.

construct-tree
`-- my-new-stack
     `-- level2-vpc
          |-- Resource
          |-- PublicSubnet1
          |    |-- Subnet
          |    |-- Acl
          |    |-- RouteTable
          |    |-- RouteTableAssociation
          |    |-- DefaultRoute
          |    |-- EIP
          |    `-- NATGateway
          |-- PublicSubnet2
          |    |-- Subnet
          |    |-- Acl
          |    |-- RouteTable
          |    |-- RouteTableAssociation
          |    |-- DefaultRoute
          |    |-- EIP
          |    `-- NATGateway
          |-- PublicSubnet3
          |    |-- Subnet
          |    |-- Acl
          |    |-- RouteTable
          |    |-- RouteTableAssociation
          |    |-- DefaultRoute
          |    |-- EIP
          |    `-- NATGateway
          |-- PrivateSubnet1
          |    |-- Subnet
          |    |-- Acl
          |    |-- RouteTable
          |    |-- RouteTableAssociation
          |    `-- DefaultRoute
          |-- PrivateSubnet2
          |    |-- Subnet
          |    |-- Acl
          |    |-- RouteTable
          |    |-- RouteTableAssociation
          |    `-- DefaultRoute
          |-- PrivateSubnet3
          |    |-- Subnet
          |    |-- Acl
          |    |-- RouteTable
          |    |-- RouteTableAssociation
          |    `-- DefaultRoute
          |-- IGW
          `-- VPCGW

Level 3 Construct (Pattern)

Here I am going to use a level 3 construct called ecs pattern ApplicationLoadbalancedFargateService

new ecsPatterns.ApplicationLoadBalancedFargateService(this, 'level3-ecs-pattern', {
            taskImageOptions: {
                image: ecs.ContainerImage.fromEcrRepository(
                    ecr.Repository.fromRepositoryName(this, 'my-nginx-repo', 'nginx')
                )
            }
        })

Now when we take a look at our construct tree we can see that many resources are being created here just like with the previous level 2 examples. The big difference here is that this level 3 construct is creating resources from other libraries other than just the ecs package. We can see below the following:

• ecs (cluster, task, services)
• ec2 (load balancers, security groups, vpc, etc...)
• Cloudwatch (log groups)

  construct-tree
  `-- my-new-stack
       |-- my-nginx-repo
       |-- level3-ecs-pattern
       |    |-- LB
       |    |    |-- Resource
       |    |    |-- SecurityGroup
       |    |    |    |-- Resource
       |    |    |    `-- to mynewstacklevel3ecspatternServiceSecurityGroup4E669D7C:80
       |    |    `-- PublicListener
       |    |         |-- Resource
       |    |         `-- ECSGroup
       |    |              `-- Resource
       |    |-- LoadBalancerDNS
       |    |-- ServiceURL
       |    |-- TaskDef
       |    |    |-- TaskRole
       |    |    |    `-- Resource
       |    |    |-- Resource
       |    |    |-- web
       |    |    |    `-- LogGroup
       |    |    |         `-- Resource
       |    |    `-- ExecutionRole
       |    |         |-- Resource
       |    |         `-- DefaultPolicy
       |    |              `-- Resource
       |    `-- Service
       |         |-- Service
       |         `-- SecurityGroup
       |              |-- Resource
       |              |-- from mynewstacklevel3ecspatternLBSecurityGroup2A462752:80
       `-- EcsDefaultClusterMnL3mNNYN
            |-- Resource
            `-- Vpc
                 |-- Resource
                 |-- PublicSubnet1
                 |    |-- Subnet
                 |    |-- Acl
                 |    |-- RouteTable
                 |    |-- RouteTableAssociation
                 |    |-- DefaultRoute
                 |    |-- EIP
                 |    `-- NATGateway
                 |-- PublicSubnet2
                 |    |-- Subnet
                 |    |-- Acl
                 |    |-- RouteTable
                 |    |-- RouteTableAssociation
                 |    |-- DefaultRoute
                 |    |-- EIP
                 |    `-- NATGateway
                 |-- PrivateSubnet1
                 |    |-- Subnet
                 |    |-- Acl
                 |    |-- RouteTable
                 |    |-- RouteTableAssociation
                 |    `-- DefaultRoute
                 |-- PrivateSubnet2
                 |    |-- Subnet
                 |    |-- Acl
                 |    |-- RouteTable
                 |    |-- RouteTableAssociation
                 |    `-- DefaultRoute
                 |-- IGW
                 `-- VPCGW