This is the AWS CDK v2 Developer Guide. The older CDK v1 entered maintenance on June 1, 2022 and ended support on June 1, 2023.

Identifiers and the AWS CDK

When building AWS Cloud Development Kit (AWS CDK) apps, you will use many types of identifiers and names. To use the AWS CDK effectively and avoid errors, it is important to understand the types of identifiers.

Identifiers must be unique within the scope in which they are created; they do not need to be globally unique in your AWS CDK application.

If you attempt to create an identifier with the same value within the same scope, the AWS CDK throws an exception.

Construct IDs

The most common identifier, id, is the identifier passed as the second argument when instantiating a construct object. This identifier, like all identifiers, only needs to be unique within the scope in which it is created, which is the first argument when instantiating a construct object.

Let's look at an example where we have two constructs with the identifier MyBucket in our app. The first is defined in the scope of the stack with the identifier Stack1. The second is defined in the scope of a stack with the identifier Stack2. Because they're defined in different scopes, this doesn't cause any conflict, and they can coexist in the same app without issues.

TypeScript

import { App, Stack, StackProps } from 'aws-cdk-lib';
import { Construct } from 'constructs';
import * as s3 from 'aws-cdk-lib/aws-s3';

class MyStack extends Stack {
  constructor(scope: Construct, id: string, props: StackProps = {}) {
    super(scope, id, props);

    new s3.Bucket(this, 'MyBucket');
  }
}

const app = new App();
new MyStack(app, 'Stack1');
new MyStack(app, 'Stack2');

JavaScript

const { App , Stack } = require('aws-cdk-lib');
const s3 = require('aws-cdk-lib/aws-s3');

class MyStack extends Stack {
  constructor(scope, id, props = {}) {
    super(scope, id, props);

    new s3.Bucket(this, 'MyBucket');
  }
}

const app = new App();
new MyStack(app, 'Stack1');
new MyStack(app, 'Stack2');

Python

from aws_cdk import App, Construct, Stack, StackProps
from constructs import Construct
from aws_cdk import aws_s3 as s3

class MyStack(Stack):

    def __init__(self, scope: Construct, id: str, **kwargs):

        super().__init__(scope, id, **kwargs)
        s3.Bucket(self, "MyBucket")

app = App()
MyStack(app, 'Stack1')
MyStack(app, 'Stack2')

Java

// MyStack.java
package com.myorg;

import software.amazon.awscdk.App;
import software.amazon.awscdk.Stack;
import software.amazon.awscdk.StackProps;
import software.constructs.Construct;
import software.amazon.awscdk.services.s3.Bucket;

public class MyStack extends Stack {
    public MyStack(final Construct scope, final String id) {
        this(scope, id, null);
    }
    
    public MyStack(final Construct scope, final String id, final StackProps props) {
        super(scope, id, props);
        new Bucket(this, "MyBucket");
    }
}

// Main.java
package com.myorg;

import software.amazon.awscdk.App;

public class Main {
    public static void main(String[] args) {
        App app = new App();
        new MyStack(app, "Stack1");
        new MyStack(app, "Stack2");
    }
}

C#

using Amazon.CDK;
using constructs;
using Amazon.CDK.AWS.S3;

public class MyStack : Stack
{
    public MyStack(Construct scope, string id, IStackProps props) : base(scope, id, props)
    {
        new Bucket(this, "MyBucket");
    }
}

class Program
{
    static void Main(string[] args)
    {
        var app = new App();
        new MyStack(app, "Stack1");
        new MyStack(app, "Stack2");
    }
}

Paths

The constructs in an AWS CDK application form a hierarchy rooted in the App class. We refer to the collection of IDs from a given construct, its parent construct, its grandparent, and so on to the root of the construct tree, as a path.

The AWS CDK typically displays paths in your templates as a string. The IDs from the levels are separated by slashes, starting at the node immediately under the root App instance, which is usually a stack. For example, the paths of the two Amazon S3 bucket resources in the previous code example are Stack1/MyBucket and Stack2/MyBucket.

You can access the path of any construct programmatically, as shown in the following example. This gets the path of myConstruct (or my_construct, as Python developers would write it). Since IDs must be unique within the scope they are created, their paths are always unique within an AWS CDK application.

TypeScript

const path: string = myConstruct.node.path;

JavaScript

const path = myConstruct.node.path;

Python

path = my_construct.node.path

Java

String path = myConstruct.getNode().getPath();

C#

string path = myConstruct.Node.Path;

Unique IDs

AWS CloudFormation requires that all logical IDs in a template be unique. Because of this, the AWS CDK must be able to generate a unique identifier for each construct in an application. Resources have paths that are globally unique (the names of all scopes from the stack to a specific resource). Therefore, the AWS CDK generates the necessary unique identifiers by concatenating the elements of the path and adding an 8-digit hash. (The hash is necessary to distinguish distinct paths, such as A/B/C and A/BC, that would result in the same AWS CloudFormation identifier. AWS CloudFormation identifiers are alphanumeric and cannot contain slashes or other separator characters.) The AWS CDK calls this string the unique ID of the construct.

In general, your AWS CDK app should not need to know about unique IDs. You can, however, access the unique ID of any construct programmatically, as shown in the following example.

TypeScript

const uid: string = Names.uniqueId(myConstruct);

JavaScript

const uid = Names.uniqueId(myConstruct);

Python

uid = Names.unique_id(my_construct)

Java

String uid = Names.uniqueId(myConstruct);

C#

string uid = Names.Uniqueid(myConstruct);

The address is another kind of unique identifier that uniquely distinguishes CDK resources. Derived from the SHA-1 hash of the path, it is not human-readable. However, its constant, relatively short length (always 42 hexadecimal characters) makes it useful in situations where the "traditional" unique ID might be too long. Some constructs may use the address in the synthesized AWS CloudFormation template instead of the unique ID. Again, your app generally should not need to know about its constructs' addresses, but you can retrieve a construct's address as follows.

TypeScript

const addr: string = myConstruct.node.addr;

JavaScript

const addr = myConstruct.node.addr;

Python

addr = my_construct.node.addr

Java

String addr = myConstruct.getNode().getAddr();

C#

string addr = myConstruct.Node.Addr;

Logical IDs

Unique IDs serve as the logical identifiers (or logical names) of resources in the generated AWS CloudFormation templates for constructs that represent AWS resources.

For example, the Amazon S3 bucket in the previous example that is created within Stack2 results in an AWS::S3::Bucket resource. The resource's logical ID is Stack2MyBucket4DD88B4F in the resulting AWS CloudFormation template. (For details on how this identifier is generated, see Unique IDs.)

Logical ID stability

Avoid changing the logical ID of a resource after it has been created. AWS CloudFormation identifies resources by their logical ID. Therefore, if you change the logical ID of a resource, AWS CloudFormation creates a new resource with the new logical ID, then deletes the existing one. Depending on the type of resource, this might cause service interruption, data loss, or both.