Sort generated subnet CIDRs when specified with newbits only

[devoncrouse]

Community Note

• Please vote on this issue by adding a 👍 reaction to the original issue to help the community and maintainers prioritize this request
• Please do not leave "+1" or "me too" comments, they generate extra noise for issue followers and do not help prioritize the request
• If you are interested in working on this issue or have submitted a pull request, please leave a comment

Description

The subnets input variable can be defined using only the newbits parameter for each entry (default), using the cidrsubnets function internally to calculate starting addresses within the VCN. This may lead to sub-optimal utilization and fragmentation of addresses depending on size and ordering.

To overcome this, we can sort the configured subnets by newbits in provided arguments to cidrsubnets, however this is non-trivial due to the way Terraform maps are ordered implicitly; we will need transformations to e.g. prefix/split map keys internally to preserve an explicit ordering.

New or Affected Resource(s)

module.network.module.network.oci_core_subnet.oke[*]

Potential Terraform Configuration

subnets = {
    bastion  = { newbits = 13 }
    operator = { newbits = 13 }
    cp       = { newbits = 13 }
    int_lb   = { newbits = 11 }
    pub_lb   = { newbits = 11 }
    workers  = { newbits = 4 }
    pods     = { newbits = 2 }
}

References

• Argument order provided to cidrsubnets can wastefully exhaust IP range hashicorp/terraform#26013
• Terraform cidrsubnets function