Sharing Resources across Stacks in AWS CDK
When building a CDK App, there is a good chance you want to structurize your project and set up multiple stacks when creating the Infrastructure. Therefore it's good to know how you can reference resources across stacks in AWS CDK.
For the example in this blog post we're going to create two stacks:
-
SharedInfraStack, which contains the VPC resource -
RdsStackwhich will import the VPC from theSharedInfraStack
Note: if you're still a beginner with AWS CDK. Then I would first recommend you to read my article on How to setup AWS CDK - complete guide.
https://towardsthecloud.com/how-to-set-up-aws-cdk
To be able to share resources between stacks in AWS CDK we need to:
- Create
SharedInfraStackwhich provisions the VPC - Pass the props of the VPC to the
RdsStackwe instantiate - Create the
RdsStackand import the VPC as prop - TL;DR give me the code!
Create SharedInfraStack which provisions the VPC
In the example below I share the share infra stack which provisions the VPC resource including subnets and routing.
// file: lib/shared-infra-stack.ts
import * as cdk from "@aws-cdk/core";
import * as ec2 from "@aws-cdk/aws-ec2";
export class SharedInfraStack extends cdk.Stack {
public readonly vpc: ec2.Vpc;
constructor(scope: cdk.App, id: string, props?: cdk.StackProps) {
super(scope, id, props);
// assign a VPC to the class property SharedInfraStack
this.vpc = new ec2.Vpc(this, "TheVPC", {
cidr: "10.0.0.0/16",
natGateways: 1,
maxAzs: 3,
subnetConfiguration: [
{
cidrMask: 20,
name: "public",
subnetType: ec2.SubnetType.PUBLIC,
},
{
cidrMask: 20,
name: "application",
subnetType: ec2.SubnetType.PRIVATE,
},
{
cidrMask: 20,
name: "data",
subnetType: ec2.SubnetType.ISOLATED,
},
],
});
}
}
If you generate the CloudFormation template by running cdk synth you'll see that the following VPC resources are being exported.
# Generated CloudFormation template of the SharedInfraStack
Outputs:
ExportsOutputRefTheVPCdataSubnet1Subnet62F6C85A8DFF3A46:
Value:
Ref: TheVPCdataSubnet1Subnet62F6C85A
Export:
Name: SharedInfraStack:ExportsOutputRefTheVPCdataSubnet1Subnet62F6C85A8DFF3A46
ExportsOutputRefTheVPCdataSubnet2SubnetAE4EF5CAD340846A:
Value:
Ref: TheVPCdataSubnet2SubnetAE4EF5CA
Export:
Name: SharedInfraStack:ExportsOutputRefTheVPCdataSubnet2SubnetAE4EF5CAD340846A
ExportsOutputRefTheVPC92636AB00B2A4A70:
Value:
Ref: TheVPC92636AB0
Export:
Name: SharedInfraStack:ExportsOutputRefTheVPC92636AB00B2A4A70
Pass the props of the VPC to the RdsStack we instantiate
In the bin folder where we instantiate the CDK app, we also declare the CDK stacks. Here we make sure to pass the props we just created from the VPC stack and pass them to the new RdsStack that we're going to create.
// file: bin/index.ts
import * as cdk from "@aws-cdk/core";
import { SharedInfraStack } from "../lib/shared-infra-stack";
import { RdsStack } from "../lib/rds-stack";
const app = new cdk.App();
// created the SharedInfraStack with the VPC resource that we're going to share by making a variable
const infra = new SharedInfraStack(app, "SharedInfraStack");
// pass the vpc resource from the SharedInfraStack to the RdsStack
new RdsStack(app, "RdsStack", {
vpc: infra.vpc,
});
Create the RdsStack and import the VPC as prop
Now we'll create the RdsStack that provisions the RDS with the VPC resource we shared across stacks in the previous two steps.
// file: lib/rds-stack.ts
import * as cdk from "@aws-cdk/core";
import * as ec2 from "@aws-cdk/aws-ec2";
import * as rds from "@aws-cdk/aws-rds";
// extend the props of the stack by adding the vpc type from the SharedInfraStack
export interface RDSStackProps extends cdk.StackProps {
vpc: ec2.Vpc;
}
export class RdsStack extends cdk.Stack {
readonly postgreSQLinstance: rds.DatabaseInstance;
private vpc: ec2.Vpc;
constructor(scope: cdk.Construct, id: string, props: RDSStackProps) {
super(scope, id, props);
// make the vpc variable accessible
const vpc = props.vpc;
const cluster = new rds.DatabaseCluster(this, "Database", {
engine: rds.DatabaseClusterEngine.auroraMysql({
version: rds.AuroraMysqlEngineVersion.VER_2_08_1,
}),
credentials: rds.Credentials.fromGeneratedSecret("clusteradmin"), // Optional - will default to 'admin' username and generated password
instanceProps: {
// optional , defaults to t3.medium
instanceType: ec2.InstanceType.of(
ec2.InstanceClass.BURSTABLE2,
ec2.InstanceSize.SMALL
),
vpcSubnets: {
subnetType: ec2.SubnetType.ISOLATED,
},
// select the vpc we imported to define the subnets for the RDS
vpc,
},
});
}
}
This is what the end result looks like when we generate the CloudFormation template with cdk synth command:
DatabaseSubnets56F17B9A:
Type: AWS::RDS::DBSubnetGroup
Properties:
DBSubnetGroupDescription: Subnets for Database database
SubnetIds:
- Fn::ImportValue: SharedInfraStack:ExportsOutputRefTheVPCdataSubnet1Subnet62F6C85A8DFF3A46
- Fn::ImportValue: SharedInfraStack:ExportsOutputRefTheVPCdataSubnet2SubnetAE4EF5CAD340846A
Metadata:
aws:cdk:path: RdsStack/Database/Subnets/Default
DatabaseB269D8BB:
Type: AWS::RDS::DBCluster
Properties:
Engine: aurora-mysql
DBClusterParameterGroupName: default.aurora-mysql5.7
DBSubnetGroupName:
Ref: DatabaseSubnets56F17B9A
EngineVersion: 5.7.mysql_aurora.2.08.1
MasterUsername: clusteradmin
MasterUserPassword:
Fn::Join:
- ""
- - "{{resolve:secretsmanager:"
- Ref: RdsStackDatabaseSecretECD539873fdaad7efa858a3daf9490cf0a702aeb
- :SecretString:password::}}
VpcSecurityGroupIds:
- Fn::GetAtt:
- DatabaseSecurityGroup5C91FDCB
- GroupId
UpdateReplacePolicy: Snapshot
DeletionPolicy: Snapshot
Metadata:
aws:cdk:path: RdsStack/Database/Resource
As you can see in the CloudFormation template we import the VPC value in the RdsStack that we've exported from the SharedInfraStack template.
TL;DR give me the code!
The code for this article is available on GitHub
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