replace_triggered_by alternative prior to terraform 1.2

Question

I have requirement to re-create the VM when hardware shapes changes. replace_triggered_by is one of the possible solution when shape changes VM can be replace easily, however we have constraints for terraform version and can not use version 1.X. Can anyone provide a solution for terraform version <= 0.13.

resource "null_resource" "shape_trigger" {
  triggers = {
    node_shape = var.etcd_shape
  }
}

// based on above trigger recerated the below resource. 

resource "oci_core_instance" "my_instance" {
  
}

Tried to do depends_on but it only updates, doesn't create the instance.

Answer 1

With an old version of terraform you are going to face many more issues, and just like replace_triggered_by a simple solution is available in a newer version; terraform is evolving very fast and constantly adding great new features, get the team to create plan to update often.

---

So if you are absolutely stuck and have to do it with the old version, your only option is to look at the source code of the resource you are working with, in your case is the oci_core_instance and see what argument has the ForceNew set to true, here is the code:
https://github.com/oracle/terraform-provider-oci/blob/master/internal/service/core/core_instance_resource.go#L29

func CoreInstanceResource() *schema.Resource {
    return &schema.Resource{
        Importer: &schema.ResourceImporter{
            State: schema.ImportStatePassthrough,
        },
        Timeouts: &schema.ResourceTimeout{
            Create: tfresource.GetTimeoutDuration("45m"),
            Update: tfresource.GetTimeoutDuration("45m"),
            Delete: tfresource.GetTimeoutDuration("75m"),
        },
        Create: createCoreInstance,
        Read:   readCoreInstance,
        Update: updateCoreInstance,
        Delete: deleteCoreInstance,
        Schema: map[string]*schema.Schema{
            // Required
            "availability_domain": {
                Type:             schema.TypeString,
                Required:         true,
                ForceNew:         true,
                DiffSuppressFunc: tfresource.EqualIgnoreCaseSuppressDiff,
            },
            "compartment_id": {
                Type:     schema.TypeString,
                Required: true,
            },
    ...

See there if availability_domain changes it forces a new resource...

Then look for a way to incorporate the variable you need var.etcd_shape in that argument, looking at all the arguments there maybe the ipxe_script is something you can use just add that variable as a comment in the script.