cidrsubnet terraform function analog

[vaspahomov]

Hi!

There is useful terraform function cidrsubnet Can we implement it in provider-aws to make easier subnet cidr specification?

What problem are you facing?

User story: AWS can provide autogenerated IPv6 cidr for VPC. (I've made PR #881 with AmazonProvidedIpv6CIDRBlock option support.) And for now there are no autogeneration support for subnet cidrs.

How could Crossplane help solve your problem?

Support function that fill 'newbits' in provided ipv6 prefix.

ipv6CIDR spec block example

ipv6CIDR:
  newbits: 4
  netnum: 64

[github-actions[bot]]

Crossplane does not currently have enough maintainers to address every issue and pull request. This issue has been automatically marked as stale because it has had no activity in the last 90 days. It will be closed in 14 days if no further activity occurs. Leaving a comment starting with /fresh will mark this issue as not stale.

[willjw1]

/fresh we use IPAM to get a cidrblock and need to split that cidrblock into subnets, how do you do this in crossplane?

[bobh66]

This Composition Function should help - https://github.com/upbound/function-cidr

[willjw1]

I think that will do exactly what we want. So I'm attempting to use it now but I'm getting an error attempting to use the function: 0s Warning ComposeResources kcv/crossplane-wt-5zcml cannot compose resources: pipeline step "cidr-block" returned a fatal result: invalid Function input: parameters: Required value: cidrFunc is required

looking at the examples I'm attempting to put this into a step by itself:

  - step: cidr-block
    functionRef:
      name: upbound-function-cidr
    input:
      apiVersion: platform.upbound.io/v1alpha1
      kind: XCIDR
      metadata:
        name: cidr-subnet
      spec:
        parameters:
          cidrFunc: cidrsubnet
          cidrBlock: 123.123.123.0/24
          newBits:
            - 8
          netNum: 3
          output: status.atFunction.cidr.subnet-a

Is this not how to use it?

[bobh66]

An example composition is here: https://github.com/upbound/function-cidr/blob/main/apis/composition.yaml

apiVersion: apiextensions.crossplane.io/v1
kind: Composition
metadata:
  name: xcidrs.platform.upbound.io
spec:
  compositeTypeRef:
    apiVersion: platform.upbound.io/v1alpha1
    kind: XCIDR
  mode: Pipeline
  pipeline:
    - step: cidr
      functionRef:
        name: upbound-function-cidr
      input:
        apiVersion: cidr.fn.crossplane.io/v1beta1
        kind: Parameters
        cidrFunc: spec.parameters.cidrFunc
        prefixField: spec.parameters.cidrBlock
        newBitsField: spec.parameters.newBits
        netNumItemsField: spec.parameters.azs
        hostNumField: spec.parameters.hostNum
        offsetField: spec.parameters.offset
        outputField: spec.parameters.output

[willjw1]

ok, so this worked about the way I expected and I'm feeling good about that:

  - step: cidr-block
    functionRef:
      name: upbound-function-cidr
    input:
      apiVersion: cidr.fn.crossplane.io/v1beta1
      kind: Parameters
      cidrFunc: cidrsubnets
      prefix: "123.123.123.0/24"
      newBits:
      - 2
      - 2
      - 2
      - 2
      outputField: status.subnets

to which I can now see in my Claim:

status:
  subnets:
  - 123.123.123.0/26
  - 123.123.123.64/26
  - 123.123.123.128/26
  - 123.123.123.192/26
  vpcCidr: 123.123.123.0/24

So success!

Next, I'd like to take the output of the vpc creation(from IPAM) which I've put into status.vpcCidr and have that feed into the prefix. How would I do that?

[willjw1]

ok so I thought that if I left out the prefix field and attempted to patch it I'd be able to put in the prefix from the vpcCidr. So something like this:

spec:
  pipeline:
  - step: cidr-block
    functionRef:
      name: upbound-function-cidr
    input:
      apiVersion: cidr.fn.crossplane.io/v1beta1
      kind: Parameters
      cidrFunc: cidrsubnets
      newBits:
      - 2
      - 2
      - 2
      - 2
      outputField: status.subnets
      patches:
        - fromFieldPath: status.vpcCidr
          toFieldPath: input.prefix
          type: FromCompositeFieldPath

this doesn't work and gives me the following: 'cannot compose resources: pipeline step "cidr-block" returned a fatal result: invalid Function input: parameters: Required value: either prefix or prefixfield function input is required'

So any ideas how this is accomplished?

[willjw1]

I joined the slack channel, and found this: https://github.com/upbound/function-cidr/issues/32 which convinces me that what I'm looking for isn't there yet.