AWS CDK Dependencies: Inferred References and addDependency

Call dependent.node.addDependency(prerequisite) when one resource must be created after another and their properties do not already express that relationship. CDK translates construct dependencies into CloudFormation ordering where applicable.

First check whether a reference already establishes the order. Passing a VPC to an EC2 construct, for example, creates references to network resources. Adding the same ordering manually is usually unnecessary.

A database and client example

The following stack demonstrates the syntax. It creates billable resources and deliberately omits application startup code. Instantiate DependencyStack from a CDK v2 app:

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import { Stack, StackProps } from "aws-cdk-lib";
import * as ec2 from "aws-cdk-lib/aws-ec2";
import * as rds from "aws-cdk-lib/aws-rds";
import { Construct } from "constructs";

export class DependencyStack extends Stack {
  constructor(scope: Construct, id: string, props?: StackProps) {
    super(scope, id, props);
    const vpc = new ec2.Vpc(this, "Network", {
      maxAzs: 2,
      natGateways: 0,
      subnetConfiguration: [{
        name: "isolated", subnetType: ec2.SubnetType.PRIVATE_ISOLATED, cidrMask: 24,
      }],
    });
    const database = new rds.DatabaseInstance(this, "Database", {
      vpc,
      vpcSubnets: { subnetType: ec2.SubnetType.PRIVATE_ISOLATED },
      engine: rds.DatabaseInstanceEngine.postgres({ version: rds.PostgresEngineVersion.VER_16 }),
      instanceType: ec2.InstanceType.of(ec2.InstanceClass.BURSTABLE3, ec2.InstanceSize.MICRO),
      storageEncrypted: true,
      publiclyAccessible: false,
    });
    const client = new ec2.Instance(this, "Client", {
      vpc,
      vpcSubnets: { subnetType: ec2.SubnetType.PRIVATE_ISOLATED },
      instanceType: ec2.InstanceType.of(ec2.InstanceClass.BURSTABLE3, ec2.InstanceSize.MICRO),
      machineImage: ec2.MachineImage.latestAmazonLinux2023(),
    });
    client.node.addDependency(database);
  }
}

The client variable avoids shadowing the ec2 namespace. The explicit dependency says to complete creation of the database resource before creating the client. It does not configure database ingress, supply credentials, install a database client, or run a migration.

This example targets CDK 2.272.0 and constructs 10.5.0 and has not been deployed to AWS. Use the full RDS and EC2 guide for connection configuration.

What to inspect during synthesis

Run npx tsc --noEmit, then npx aws-cdk synth. Inspect the EC2 resource's DependsOn and references. A dependency from A to B means B is created first; it does not mean A triggers a replacement every time B changes.

For stacks, consumerStack.addDependency(producerStack) controls deployment order. For values shared across stacks, understand outputs and exports; a dependency alone does not transmit a value.

Avoid circular dependencies

If A depends on B and B depends on A, adding more explicit dependencies cannot resolve the cycle. Inspect references, security-group rules, and resource ownership. Move the shared interface or a separately managed rule to a place that breaks the cycle.

AWS documents ordering semantics in CloudFormation DependsOn. Runtime readiness still belongs in application retries, health checks, or a deliberately designed initialization workflow.

Review cdk diff before deployment. On cleanup, the database's default snapshot policy may preserve data and incur storage charges; inspect the proposal and retained resources rather than assuming destroy removes everything.