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# golang
s
swift-machine-98066
10/21/2022, 7:04 PMdoes anyone dynamically make subnets from a cidr using the number of available availability zones?
b
bored-table-20691
10/28/2022, 5:26 AMI kind of do this, though not exactly.
s
swift-machine-98066
10/31/2022, 6:08 PMhow are you doing it?
b
bored-table-20691
10/31/2022, 6:10 PM Copy code
state := "available"
availableAZ, err := aws.GetAvailabilityZones(ctx, &aws.GetAvailabilityZonesArgs{
State: &state,
}, pulumi.Provider(awsProvider))
if err != nil {
return nil, err
}
subnets := make([]*ec2.Subnet, 0, 8)
privateCidrs := make([]string, 0, 8)
publicCidrs := make([]string, 0, 8)
privateSubnetIDs := make([]pulumi.StringOutput, 0, 8)
publicSubnetIDs := make([]pulumi.StringOutput, 0, 8)
privateSubnetNames := make([]string, 0, 8)
publicSubnetNames := make([]string, 0, 8)
privateSubnetRouteTables := make([]*ec2.RouteTable, 0, 8)
publicSubnetRouteTables := make([]*ec2.RouteTable, 0, 8)
vpcCidrAssociations := make([]pulumi.Resource, 0, 8)
natGateways := make([]*ec2.NatGateway, 0, 8)
azNames := availableAZ.Names
sort.Strings(azNames)
for idx, az := range azNames {
// Ignore it if we have more than 4 AZs
if idx > 3 {
continue
}
publicCidr := cidrs.Public[idx]
privateCidr := cidrs.Private[idx]
publicCidrs = append(publicCidrs, publicCidr)
privateCidrs = append(privateCidrs, privateCidr)
publicAssoc, err := ec2.NewVpcIpv4CidrBlockAssociation(ctx, fmt.Sprintf("okera-ssa-vpc-cidr-public-%s", az), &ec2.VpcIpv4CidrBlockAssociationArgs{
VpcId: vpc.ID(),
CidrBlock: pulumi.String(publicCidr),
}, pulumi.Provider(awsProvider))
if err != nil {
return nil, err
}
privateAssoc, err := ec2.NewVpcIpv4CidrBlockAssociation(ctx, fmt.Sprintf("okera-ssa-vpc-cidr-private-%s", az), &ec2.VpcIpv4CidrBlockAssociationArgs{
VpcId: vpc.ID(),
CidrBlock: pulumi.String(privateCidr),
}, pulumi.Provider(awsProvider))
if err != nil {
return nil, err
}
publicSubnetName := fmt.Sprintf("subnet-ssa-public-%s", az)
publicSubnet, err := ec2.NewSubnet(ctx, publicSubnetName, &ec2.SubnetArgs{
VpcId: vpc.ID(),
CidrBlock: publicAssoc.CidrBlock,
AvailabilityZone: pulumi.String(az),
MapPublicIpOnLaunch: pulumi.Bool(true),
Tags: pulumi.StringMap{
"Name": pulumi.String(fmt.Sprintf("%s-%s-%s", ctx.Stack(), "public", az)),
},
}, pulumi.Provider(awsProvider))
if err != nil {I’m eliding some things here, but to give you a sense
The CIDRs are pre-defined in the Pulumi config file, but in a prior version of the code it dynamically computed them
Based on a starting IP
s
swift-machine-98066
10/31/2022, 6:13 PMyeah we are doing something like this
Copy code
config:
network:createVPCs: true
network:data:
regions:
- us-east-1:
vpcs:
- my-vpc-us-east-1:
vpc-cidr: 10.20.0.0/16
availability-zones:
- us-east-1c
- us-east-1d
- us-east-1e
data-cidrs:
- 10.20.100.0/24
- 10.20.101.0/24
- 10.20.102.0/24
app-cidrs:
- 10.20.200.0/24
- 10.20.201.0/24
- 10.20.202.0/24
pub-cidrs:
- 10.20.180.0/24
- 10.20.181.0/24
- 10.20.182.0/24b
bored-table-20691
10/31/2022, 6:19 PMYeah, it’s definitely possible
You can see from the code snippet I posted that the AZs are fetched dynamically, and auto-calculating the CIDR (+ a size and starting IP) from that is relatively simple
In the end though, I had decided that I wanted more control over the CIDRs since it falls under overall network management, and didn’t want it going out of control (or a simple arithmetic change meaning I would need to destroy my subnets and everything attached to them.
s
swift-machine-98066
11/01/2022, 1:47 PMahh makes sense
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