Hi all. I using Pulumi with the Go SDK and try to understand how I can exactly use dependsOn. I am creating subnets in AWS and then want to use some of those to create a TGW attachment. For the latter, I need SubnetIds, which is an array of StringArrayInput. My problem is, the subnet resource only provides an ID of type pulumi.IDOutput. There's no straightforward way to convert this to a string right? What should I be using/doing instead here?

Unfortunately, type conversions in Go are tedious by nature. We have some helpers in the SDK, like

func ToStringArrayOutput(in []StringOutput)

but they don’t cover all cases. Here’s a deeper discussion if you’re interested.

I’m using this approach, which seems to work fine (

numOfAZs

is a count of how many AZs are in the specified region):

// Create private subnets in the VPC
privSubnetIds := make([]pulumi.StringInput, numOfAZs)
for idx := 0; idx < numOfAZs; idx++ {
	subnetAddr := (idx * 32) + 16
	subnetCidrBlock := fmt.Sprintf("%s%d.0/22", netAddrMap[awsRegion], subnetAddr)
	subnet, err := ec2.NewSubnet(ctx, fmt.Sprintf("priv-subnet-%d", idx), &ec2.SubnetArgs{
		VpcId:               vpc.ID(),
		AvailabilityZone:    pulumi.String(azNames[idx]),
		CidrBlock:           pulumi.String(subnetCidrBlock),
		MapPublicIpOnLaunch: pulumi.Bool(false),
		Tags: pulumi.StringMap{
			"Name":    pulumi.Sprintf("%s-priv-%d", baseName, idx),
		},
	})
	if err != nil {
		log.Printf("error creating private subnet: %s", err.Error())
	}
	privSubnetIds[idx] = subnet.ID()
}

Thank you Scott, I will try and see if this works for me. Because your code also calculates the subnets, which our Terraform stack did with its own function before. Until now, I just resented to declaring the subnets explicitly in the config (which is fine), but creating them dynamically leads to less repetition

I’ve been looking for a better/smarter/more resilient way to handle the subnet calculations, but I haven’t gotten there yet. (BTW, I don’t use AWSX because I need a tad more flexibility than the high-level VPC component offers. However, it’s very useful for the vast majority of straightforward implementations.)

update on this: I spent the day and wrote my own Go implementation of the Terraform cidrsubnet function. Works just the same, takes a CIDR, number of additional bits and index of the subnet in the available range and returns it. Added unittests, so now I have a robust way of doing what I could before :)

Sweet! Have you published that code anywhere? 🙂

Since I worked on this during company hours and for my company, I am unsure if am allowed to share it (even if it's completely generic and has of course no reference to anything from my company). I will check that tomorrow and will get back to you! Would be happy to share if possible, to give something back to the community

Totally understand, no worries at all!