DatabaseCluster: Cluster requires at least 2 subnets, got 1

[maymayman]

Describe the bug

Expected Behavior

DatabaseCluster can init successful

Current Behavior

Cluster requires at least 2 subnets, got 1

Reproduction Steps

in First Stack i create a VPC
this.mainVpc = new Vpc(this, mainVpcName, { ipAddresses: IpAddresses.cidr('192.168.0.0/16'), vpcName: mainVpcName, maxAzs: 2, enableDnsHostnames: true, enableDnsSupport: true, natGateways: 1, subnetConfiguration: [ { name: 'public-subnet-1', subnetType: SubnetType.PUBLIC, cidrMask: 20, }, { name: 'isolated-subnet-1', subnetType: SubnetType.PRIVATE_ISOLATED, cidrMask: 18, }, ], });

and Next stack I use fromLookup to retrieve that VPC
const mainVpc: IVpc = Vpc.fromLookup(this, mainVpcName, { vpcName: mainVpcName, region: props.env?.region, });

and then create a DatabaseCluster like above

Possible Solution

No response

Additional Information/Context

No response

CDK CLI Version

2.64.0

Framework Version

No response

Node.js Version

16.17

OS

Window

Language

Typescript

Language Version

3.9.7

Other information

"aws-cdk": "2.64.0",
"aws-cdk-lib": "2.64.0",
"constructs": "10.1.246",

[pahud]

Let me reproduce the VPC as yours.

[pahud]

Hi

If you create your vpc like below, you can list all the public subnet IDs like this:

      const vpc = new ec2.Vpc(this, 'Vpc', { 
        ipAddresses: ec2.IpAddresses.cidr('192.168.0.0/16'), 
        maxAzs: 2, 
        enableDnsHostnames: true, 
        enableDnsSupport: true, 
        natGateways: 1, 
        subnetConfiguration: [ 
          { name: 'public-subnet-1', subnetType: ec2.SubnetType.PUBLIC, cidrMask: 20, }, 
          { name: 'isolated-subnet-1', subnetType: ec2.SubnetType.PRIVATE_ISOLATED, cidrMask: 18, }, 
        ], 
      });

      const mysubnets = vpc.selectSubnets({ subnetType: ec2.SubnetType.PUBLIC }).subnetIds.join(',')
      new CfnOutput(this, 'SubnetIDs', { value: mysubnets })

In my case, I got the output indicating 2 public subnets selected.

Outputs:
demo-dev2.SubnetIDs = subnet-066a7a9f7353d0e53,subnet-03c55f805018bfafb

So I would be confident that { subnetType: ec2.SubnetType.PUBLIC } should select 2 existing public subnets and I can pass this to the vpcSubnets required for DatabaseCluster.instanceProps.

Can you check your vpc selection and make sure it turns 2 subnets?

[JobaDiniz]

For whoever arrives here with the same issue as me, the problem I had is I set MaxAz=1. You need to set MaxAzs=2 at least.