HI friends, im creating a new VPC using the terraform <https://github.com/terraform-aws-modules/terraform-aws-vpc> module.
I would like to understand the separation of the subnets a little better.
public_subnets = [for k, v in local.azs : cidrsubnet(local.vpc_cidr, 6, k + 4)]
database_subnets = [for k, v in local.azs : cidrsubnet(local.vpc_cidr, 6, k + 8)]```
In total i end up with 9 subnets. I chose /22 so that i have a larger 1024 available ip addresses to work with.
One thing i don't understand is the gap in between them for example. What is the purpose of this and why?
4->8
```10.1.4.0/22 -> 10.1.8.0/22```
```vpc-private-us-east-2a 10.1.0.0/22
vpc-private-us-east-2b 10.1.4.0/22
vpc-private-us-east-2c 10.1.8.0/22
vpc-public-us-east-2a 10.1.16.0/22
vpc-public-us-east-2b 10.1.20.0/22
vpc-public-us-east-2c 10.1.24.0/22
vpc-db-us-east-2a 10.1.32.0/22
vpc-db-us-east-2b 10.1.36.0/22
vpc-db-us-east-2c 10.1.40.0/22```
Is it just because IP subnetting is binary, and therefore splits subnets nicely in 2s/4s/8s etc, but because you’re using 3 x AZs, there is a “spare” subnet?
10.1.12.0/22 “spare private subnet”
10.1.28.0/22 “spare public subnet”
10.1.44.0/22 “spare db subnet”
Using that site i can divide it to 1022 hosts, i can see the subnet increments by 4s everytime.
But in the above example i have created using terraform i can see between public, private, db subnet groups there is a gap of 8, is there some reason for that?
