Allow modification to Ports section for FixedIP addition

[sachinphogat]

/kind feature

Describe the solution you'd like
Allow addition of FixedIP post openstackmachine creation. This will help implement external IPAM solution. Post OpenstackMachine is created, I have developed external validating webhook to block OpenstackServer creation so that IPAM system will add FixedIP to openstack machine and validating webhook will let OpenstackServer to be created.

We need to allow modification to Ports spec for FixedIP addition post creation.

[EmilienM]

The OpenStackMachine is immutable, I don't think we can do that, right @mdbooth ?

[sachinphogat]

Can we enhance by allowing this through validating webhook?

[mdbooth]

@sachinphogat As @EmilienM says machines are immutable, but this is more about 'we don't modify them after they've been created'. However, I think it could be valid, e.g. to use a lifecycle hook which prevents creation until external actors have had an opportunity to modify the object.

Can you do me a favour? Please can you start a conversation in #cluster-api slack about this and gather some ways others have achieved it and link that conversation here? I have a feeling it should involve lifecycle hooks rather than a mutating webhook, but I haven't done enough reading about how they are implemented to be sure.

I think this is a valid and interesting use case. Thanks!

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