I am trying to write a Pulumi script to create a new volume and also support attaching the create volume to the instance (in case the instance is deleted and replaced) in every update.

In that case I think you just need an

aws.ec2.EbsVolume

resource and an

aws.ec2.EbsVolumeAttachment

resource

and how do I ensure that the existing EbsVolume is attached to the instance in case the instance was replaced?

That’s what the attachment resource does